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Articoli di riviste sul tema "Granulats naturels"
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El Maghri, Sanaa, Samia Yousfi, Hicham Essallaki e Mouna Latifa Bouamrani. "Étude de l’effet de l’ajout des déchets de marbre sur les propriétés du béton à base de granulats de briques recyclés (GBR)". Matériaux & Techniques 110, n. 5 (2022): 502. http://dx.doi.org/10.1051/mattech/2022032.
Testo completoAbstract (sommario):
Le présent travail vise à valoriser les déchets issus de l’industrie des matériaux de construction à savoir les débris des briques en terre cuite des briqueteries et les déchets de marbre. Pour atteindre cet objectif de valorisation des déchets inertes, non dangereux issus de l’industrie des matériaux de construction, il est impératif de développer des systèmes de recyclage de ces déchets. C’est dans cette optique que nous proposons, dans ce travail, de recycler les déchets de briques en terre cuite ainsi que les déchets de marbre. Il s’agit d’une étude expérimentale où différentes formulations des bétons ont été préparées à partir d’une formulation de référence avec des granulats naturels. Une substitution partielle avec des taux de 20 %, 40 %, 60 % jusqu’à une substitution totale de 100 % a été réalisée. Les bétons ainsi fabriqués ont été caractérisés afin d’évaluer leurs performances en comparaison avec celles du béton de référence. Les résultats de cette étude ont prouvé que les meilleures performances du béton sont obtenues pour un taux de 20 % et 40 % de substitution. Ces résultats ont été améliorés par l’ajout des déchets de marbre sous forme de poudre, avec différents taux (5 %, 10 % et 15 %). La qualité des bétons ainsi fabriqués a été améliorée. Ainsi, ces granulats recyclés peuvent être employés à la place de granulats naturels dans de nouvelles constructions en suivant la norme EN 206 qui réglemente leur utilisation selon leurs caractéristiques et la classe d’exposition des ouvrages construits.
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Mejía de Gutiérrez, R., R. A. Robayo e M. Gordillo. "Natural pozzolan-and granulated blast furnace slag-based binary geopolymers". Materiales de Construcción 66, n. 321 (18 gennaio 2016): e077. http://dx.doi.org/10.3989/mc.2016.03615.
Testo completo
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Mascena, Jonadabe Lauvers dos Santos, e João Paulo Souza Silva. "Uso de material fresado em camadas granulares para fins de pavimentação". CONTRIBUCIONES A LAS CIENCIAS SOCIALES 17, n. 8 (9 agosto 2024): e9251. http://dx.doi.org/10.55905/revconv.17n.8-115.
Testo completoAbstract (sommario):
Este estudo analisa a eficácia do uso de Reclaimed Asphalt Pavement (RAP) na melhoria de solos para pavimentação, visando aumentar a capacidade de suporte, estabilidade e durabilidade dos solos, promovendo a sustentabilidade na engenharia. A pesquisa foi motivada pela necessidade de encontrar soluções mais sustentáveis e eficientes para a construção de pavimentos. O objetivo principal é avaliar a viabilidade técnica do uso de uma mistura composta por 40% de RAP e 60% de solo em camadas granulares de pavimentos flexíveis. Para alcançar esse objetivo, foi realizado um levantamento bibliográfico abrangendo o período de 2018 a 2024, além de ensaios laboratoriais para caracterizar o solo e o RAP, e testes de mistura e compactação. Os resultados mostraram que a mistura de solo e RAP apresentou melhorias significativas nas propriedades do solo, tornando-o mais adequado para pavimentação, com ganhos em capacidade de suporte e durabilidade. Além disso, a utilização de RAP contribui para a redução do uso de recursos naturais e a diminuição da produção de resíduos, alinhando-se com práticas de engenharia sustentável. Conclui-se que o uso de RAP em camadas granulares é uma solução sustentável e eficaz para pavimentação, proporcionando benefícios ambientais e econômicos. O uso de uma mistura composta por 40% de RAP e 60% de solo pode ser utilizado em camadas de sub-base. Este estudo destaca a importância de práticas inovadoras e sustentáveis na engenharia civil, promovendo a reutilização de materiais e a conservação dos recursos naturais.
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Flor-Chavez, Gino F., Judith A. Chalen-Medina e Zoila L. Cevallos-Revelo. "Aprovechamiento del hormigón reciclado en obras viales". Polo del Conocimiento 2, n. 6 (16 giugno 2017): 624. http://dx.doi.org/10.23857/pc.v2i6.150.
Testo completoAbstract (sommario):
<p style="text-align: justify;">El empleo de agregados reciclados obtenidos de la demolición de las estructuras de hormigón es un tema prioritario en la mayoría de países para disminuir el consumo de recursos naturales, cubrir las necesidades crecientes de materia prima y minimizar espacios para la disposición de residuos protegiendo al medio ambiente. Se estudiaron alternativas de uso de los residuos de pavimentos urbanos, a partir del análisis de un caso específico en la zona del Gran La Plata (Provincia de Buenos Aires, Argentina), donde existen numerosos pavimentos que requieren reparación y reconstrucción. Se utilizaron las fracciones fina y gruesa de agregados reciclados obtenidos a partir de la trituración de losas que eran retiradas durante una repavimentación. Luego de caracterizar estos agregados se analizaron varias alternativas de uso entre las que se incluyeron hormigones de cemento portland, pavimentos asfálticos y bases granulares. En cada caso se realizaron estudios comparativos con mezclas similares elaboradas sólo con agregados naturales. Incorporando agregado reciclado (grueso y fino) en concreto asfáltico en caliente no se obtuvieron mezclas que cumplieran los requisitos establecidos para este material, al emplear sólo la fracción fina se alcanzaron los parámetros volumétricos requeridos pero con un gran incremento de la rigidez. En cuanto al uso en bases granulares al mezclar agregado reciclado grueso y fino en diferentes porcentajes se obtuvo un Valor Soporte inferior al requerido para bases pero mayor al exigido para subbases. Referente en hormigones, las mezclas usadas como base de apoyo (hormigón pobre) no influye el uso de agregados reciclados en las propiedades ya que muestran resistencias parecidas, en cambio las mezclas usadas como capa de rodaduras, estos hormigones con agregados reciclados presentan resistencias inferiores. También incluye un análisis de los costos de cada una de las alternativas estudiadas que demuestra que para la región el uso de agregado reciclado en la elaboración de pavimentos y bases granulares, además de los beneficios ambientales, da lugar a un ahorro económico considerable comparado con mezclas similares elaboradas con agregados naturales, principalmente en lo relacionado con el costo de los materiales y su transporte. </p>
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Gottipati, Ramakrishna, Baradwaj Adiraju e Susmita Mishra. "Application of Granular Activated Carbon Developed from Agricultural Waste as a Natural Gas Storage Vehicle". International Journal of Engineering and Technology 4, n. 4 (2012): 468–20. http://dx.doi.org/10.7763/ijet.2012.v4.412.
Testo completo
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Shapakidze, Elena, Marina Avaliani, Marina Nadirashvili, Vera Maisuradze, Ioseb Gejadze e Tamar Petriashvili. "Synthesis and Study of Properties of Geopolymer Materials Developed Using Local Natural Raw Materials and Industrial Waste". Chemistry & Chemical Technology 17, n. 4 (25 dicembre 2023): 711–18. http://dx.doi.org/10.23939/chcht17.04.711.
Testo completoAbstract (sommario):
This paper describes the synthesis of geopolymer materials using thermally modified clay rocks of Georgia and metallurgical granulated blast-furnace slag; as well as the study of their physical and mechanical properties, durability, and corrosion resistance in aggressive solutions.The methods of chemical, X-ray phase, differential thermal analysis and SEM were used.
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Santiago-Guzmán, Marina, María Eugenia Chávez-Arellano, Julio Baca del Moral e Cristóbal Santos-Cervantes. "Transformación de los sistemas de producción piloncillera en la Huasteca Potosina: el caso de Cruztujub, Fracción Cruztujub y La Garza". Textual, n. 81 (30 giugno 2023): 145–73. http://dx.doi.org/10.5154/r.textual.2021.81.09.
Testo completoAbstract (sommario):
Los piloncilleros de la Huasteca Potosina han incursionado en diversas formas de producción de piloncillo industrial pasando por la elaboración en cono, hasta la producción de granulado, con el objetivo de adecuarse al mercado y mejorar el ingreso. En este trabajo se estudian los sistemas de producción piloncilleros presentes en las localidades de Cruztujub, Fracción Cruztujub y La Garza, Tancanhuitz, San Luis Potosí, con el objetivo de exponer las estrategias de producción piloncillera que las familias campesinas de estas localidades han instrumentado como una forma de adaptación a los nuevos requerimientos del mercado, y así poder dar continuidad a su actividad. De acuerdo con los resultados obtenidos se han visto mejoras en la conversión productiva de piloncillo industrial a piloncillo granulado, sin embargo, aún resulta insuficiente garantizar la reproducción socioeconómica de las familias rurales campesinas, por lo tanto, los miembros tienden a realizar otras actividades como la comercialización de productos agrícolas, jornales y oficios. Es importante que las entidades correspondientes efectúen la promoción en el consumo de productos naturales elaborados por campesinos para impulsar la economía familiar campesina.
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Ceccato, D. M., A. B. Masuero, C. A. M. Moraes e A. C. F. Vilela. "Reciclaje de escoria granulada de fundición (EGF) como sustitución de parte del cemento en hormigón". Matéria (Rio de Janeiro) 14, n. 1 (7 aprile 2009): 737–48. http://dx.doi.org/10.1590/s1517-70762009000100008.
Testo completoAbstract (sommario):
El reciclaje de residuos sólidos industriales se ha vuelto una práctica indispensable en la preservación de los recursos naturales, en la minimización de los costos y en la reducción del impacto ambiental. La utilización de materiales alternativos en la industria de la construcción civil es una práctica económicamente atractiva y ambientalmente correcta. Siendo así, el empleo de escorias como materia prima en carreteras, hormigón y cemento ya es una práctica corriente, en la cual, el destino más noble de estos materiales reciclables depende de la existencia de características adecuadas al uso propuesto. La escoria granulada de fundición (EGF) es un residuo generado en el proceso de fusión de chatarras de hierro fundido en horno cubilote. Estudios anteriores apuntaron que esta escoria, cuando es finamente molida, presenta buenas propiedades piroclásticas (de tipo pozzolana). Además, su estructura amorfa, resultante del proceso de generación a través del enfriamiento brusco y la composición química adecuada, permiten una aplicación más noble de este residuo, como sustituto del cemento. Este trabajo tiene como objetivo estudiar el desempeño de hormigones con la utilización de escoria granulada de fundición como sustitución de parte del cemento, a través de la evaluación de sus propiedades mecánicas. Para ello fueron moldeados cuerpos de prueba de hormigón con diferentes combinaciones de tenores de sustitución de cemento por escoria granulada de fundición (10%, 30% y 50%), en volumen, y relaciones agua/aglomerante (0,40; 0,55 0,70), a ser comparadas con el hormigón de referencia (sin EGF). Para cada edad de hormigón (7, 28 y 91 días) se realizaron ensayos mecánicos, tales como la resistencia a la compresión uniaxial, resistencia a la tracción por compresión diametral y resistencia a la tracción en la flexión. Resultados muestran que la escoria granulada de fundición presenta adecuado desempeño (propiedades mecánicas) en relación a la aplicación propuesta.
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Abnelia-Rivera, Rosa, Domingo Alfonso Martín e Miguel Ángel Sanjuán. "Cementos portland ternarios elaborados con escoria granulada de alto horno molida y cenizas volantes de carbón: desempeño de resistencia a la compresión = Ternary portland cements made with ground granulated blast-furnace slag and coal fly ash: compressive strength performance". Anales de Edificación 7, n. 3 (31 dicembre 2021): 7–9. http://dx.doi.org/10.20868/ade.2021.4969.
Testo completoAbstract (sommario):
Se informó que la producción mundial de cemento Portland fue de 4650 millones de toneladas en 2016. Dicha producción de cemento exige una cantidad significativa de recursos naturales y energía. Además, la producción de una tonelada de cemento Portland emite alrededor de 0,87 toneladas de dióxido de carbono. Este valor se reduciría significativamente al utilizar cementos ternarios elaborados con residuos industriales como escoria granulada de alto horno molida (GGBFS) y cenizas volantes de carbón (CFA). Además, se promueve la economía circular mediante el uso de residuos industriales (GGBFS y CFA) y se aumenta la durabilidad del hormigón en ambientes agresivos. Por el contrario, inducen un retraso en la ganancia de resistencia a la compresión como resultado de la reacción puzolánica. En este trabajo se ensayaron mezclas ternarias de cemento con proporciones GGBFS y CFA (25% y 40%) sobre morteros estándar. En consecuencia, se realizaron medidas de resistencia a la compresión a los 2, 7 y 28 días. Se discutieron las interacciones estadísticas entre GGBFS y CFA en los resultados de resistencia a la compresión de los morteros de cemento Portland ternarios.AbstractGlobal production of Portland cement was reported to be 4.65 billion tons in 2016. Such cement production demands a significant amount of natural resources and energy. Furthermore, the production of one tonne of Portland cement emits about 0.87 tons of carbon dioxide. This value would be reduced significantly by using ternary cements made with industrial wastes such as ground granulated blast-furnace slag (GGBFS) and coal fly ash (CFA). In addition, circular economy is promoted by using industrial wastes (GGBFS and CFA) and the concrete durability in aggressive environments is increased. By contrast, they induce a delay in the compressive strength gain as result of the pozzolanic reaction. In this paper, ternary cement mixes with GGBFS and CFA proportions (25% and 40%) were tested on standard mortars. Accordingly, compressive strength measures at 2, 7 and 28 days was performed. Statistical interactions between GGBFS and CFA on the compressive strength results of ternary Portland cement mortars were discussed.
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Pagio, Mariana Zani, Lilian Favarato Carrareto, Geilma Lima Vieira e Diego Corrêa Magalhães. "Caracterização de resíduos siderúrgicos visando à aplicação em matrizes cimentícias". Ambiente Construído 22, n. 2 (giugno 2022): 167–86. http://dx.doi.org/10.1590/s1678-86212022000200599.
Testo completoAbstract (sommario):
Resumo A siderurgia, apesar de ter relevância na economia global, é responsável pela geração de um elevado volume de resíduos em sua cadeia produtiva. Buscando o desenvolvimento sustentável, a construção civil absorve resíduos siderúrgicos ao oferecer alternativas de matérias-primas e reduzir a extração de recursos naturais. Nesta pesquisa, destaca-se a análise de quatro resíduos siderúrgicos: as escórias de alto-forno (granulada e resfriada ao ar), a Terra de Shredder e o pó do despoeiramento do forno elétrico a arco (pó de FEA). Assim, o artigo tem o objetivo de caracterizar os resíduos física, química, mineralógica, microestrutural e ambientalmente, visando a sua incorporação em matrizes cimentícias. Constatou-se que a escória granulada de alto-forno possui estrutura vítrea, o que a torna um material potencialmente reativo, enquanto a escória de alto-forno resfriada ao ar se apresenta cristalina. As duas escórias possuem finura e composição química semelhantes às do cimento Portland, com predominância de SiO2 e CaO. O pó de FEA também é um material fino, com grãos em formatos esféricos e composição química rica em ferro e zinco. A Terra de Shredder tem predominância de sílica e ferro e elevada perda ao fogo, em virtude dos materiais que a compõem.
Tesi sul tema "Granulats naturels"
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Martaud, Thomas. "Evaluation environnementale de la production de granulats naturels en exploitation de carrière : indicateurs, modèles et outils". Orléans, 2008. https://tel.archives-ouvertes.fr/tel-00412080.
Testo completoAbstract (sommario):
Les granulats naturels, seconde matière première consommée en France, sont élaborés à partir de roche, ressource non renouvelable. La prise de conscience de l’importance de la protection de l’environnement et des impacts associés à l’élaboration de produits manufacturés, favorise le développement de méthodes destinées à mieux approcher les impacts de leur production. Dans ce contexte, ce travail concerne l’évaluation environnementale d’exploitations industrielles en carrière. Il s’appuie sur une collecte de données de sites utiles à cette évaluation, suivie de la réalisation d’un modèle d’évaluation globale des consommations d’énergie, rejets atmosphériques et émissions sonores générées lors de l’élaboration de granulats. Ce modèle, basé sur des indicateurs, est conçu pour être paramétrable selon la nature pétrographique du site (roche meuble ou massive). La mise au point d’un outil d’évaluation, nommé CADUR (CArrière DURable) permet i) d’obtenir des données environnementales relative à la production de granulats naturels ; ii) de mettre en évidence que le paramètre prépondérant de l’évaluation en carrière est la configuration elle-même de l’exploitation considérée ; iii) de suivre, pour l’exploitant, l’évolution de ces performances, d’en comprendre les raisons et de quantifier l’effet d’éventuelles modifications. Vis-à-vis des données de sites collectées, les résultats fournis par CADUR offrent une relative bonne précision. Ils montrent des écarts, avec les données réelles, inférieurs à 10 % pour les consommations énergétiques et à 5 % concernant les niveaux sonores.
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Clavier, Martial. "Caractérisation environnementale de matériaux de construction à l'aide de nouvelles normes de lixiviation : étude expérimentale et numérique". Electronic Thesis or Diss., CY Cergy Paris Université, 2024. http://www.theses.fr/2024CYUN1284.
Testo completoAbstract (sommario):
Avec le développement de l'économie circulaire dans le domaine de la construction, des matériaux alternatifs ont émergé à partir de sous-produits industriels et de déchets, ce qui permet de compléter l'offre en matériaux naturels traditionnels. Cependant, leur utilisation nécessite de garantir qu'ils ne libèrent pas de substances nocives lorsqu'ils entrent en contact avec l'environnement. Dans ce but, des efforts ont été réalisés en Europe ces dernières décennies pour développer des normes de lixiviation dont la durée de l'essai est censée représenter le comportement à long terme des produits de construction, lesquelles ont récemment été publiées. En parallèle, en France, des guides d'acceptabilité environnementale ont été publiés pour évaluer les performances environnementales des matériaux alternatifs utilisés dans la construction routière, s'appuyant principalement sur un essai rapide de lixiviation en batch NF EN 12457. Les différences entre les nouvelles normes européennes d'essai et cette norme de lixiviation en batch soulèvent un besoin de l'industrie de s'adapter.Cette thèse se propose d'examiner les résultats des nouveaux essais européens sur une gamme de matériaux de différentes natures et de chercher à raccourcir ces essais tout en maintenant une bonne fiabilité. La mise en place des essais et leur validation a d'abord été effectuée. Quarante-trois échantillons granulaires (naturels, recyclés, provenant de MIDND et de sédiments) de granulométries variées et dix-neuf produits monolithiques liés (béton, enrobé et MTLH) composés d'au moins un des granulats étudiés ont été caractérisés dans ces travaux par des essais de percolation à courant ascendant, de lixiviation dynamique des surfaces et/ou de lixiviation en batch. Plusieurs essais de caractérisations physico-chimiques ont été réalisés, dans le but de mieux expliquer certains mécanismes de relargage : digestion acide, MEB-EDX, DRX, essai de pH-dépendance. Enfin, une étude de corrélations empiriques entre les résultats des essais de lixiviation, et le développement d'un modèle de couplage géochimie-transport à l'aide du logiciel GEMS ont été effectués dans le but de fournir des outils pour raccourcir les essais de lixiviation. L'exploitation des résultats obtenus montre l'existence de tendances dans le relargage des substances nocives recherchées, et parfois dans leurs mécanismes de relargage, selon la nature du matériau. La granulométrie exerce une influence sur le comportement à la lixiviation, tandis que l'ajout de liant à un granulat a souvent un effet inhibiteur sur le relargage depuis ce dernier, mais induit parfois de nouveaux relargages. Des différences d'action dans la limitation des relargages depuis les granulats par les liants hydrauliques et les liants hydrocarbonés ont été mises en évidence. Les corrélations établies permettent de fournir des outils pour justifier l'utilisation d'un essai rapide de contrôle de production qui peut être soit l'essai de lixiviation en batch, soit une version plus courte des essais européens en remplacement de ces derniers. Enfin, les modèles développés prédisent correctement le relargage de certaines substances mais nécessitent une étude plus approfondie dans le but de les améliorerWith the development of the circular economy in the construction sector, alternative materials have emerged from industrial by-products and waste to reduce the use of traditional natural materials. However, their use requires ensuring that they do not release harmful substances when in contact with the environment. To this end, efforts have been made in Europe in recent decades to develop leaching standards adapted to construction products, recently published. In parallel, in France, environmental acceptability guidelines have been published to assess the environmental performance of alternative materials used in road construction, mainly based on the batch leaching standard EN 12457. The differences between the new European test standards and this standard used in France raise a need for the industry to adapt. This thesis aims to examine the results of the new European tests on a range of French materials of different natures and to seek to shorten these tests while maintaining good reliability. The setup of the tests and their validation was first carried out. Forty-three granular samples (natural, recycled, from MIDND, and sediments) of various grain sizes and nineteen monolithic products (concrete, asphalt, and MTLH) composed of at least one aggregate studied alone were characterized in this work by ascending current percolation tests, dynamic surface leaching, and/or batch leaching. Several physico-chemical characterization tests were conducted to better explain certain leaching mechanisms: acid digestion, SEM-EDX, XRD, pH-dependent test. Finally, a study of correlations between the results of leaching tests, and the development of a geochemistry-transport coupling model using the GEMS software were carried out to provide tools for shortening the tests. The results obtained show the existence of trends in the release of regulated hazardous substances, and sometimes in their release mechanisms, depending on the nature of the material. Particle size has an influence on leaching behavior, while adding binder to an aggregate often inhibits leaching from it, but sometimes induces new releases. Differences in the action of limiting releases from aggregates by hydraulic binders and hydrocarbon binders have been highlighted. The established correlations provide tools to justify the use of either batch leaching tests or short versions of European tests as replacements for the latter. Finally, the developed models correctly predict the release of certain substances but require further study to improve them
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Bouarroudj, Mohamed ElKarim. "Utilisation de matériaux naturels modèles pour la formulation de mortier contenant des sables et des fines de granulats recyclés". Thesis, Ecole nationale supérieure Mines-Télécom Lille Douai, 2019. http://www.theses.fr/2019MTLD0016.
Testo completoAbstract (sommario):
Les granulats de béton recyclé (GBR) ne sont pas suffisamment utilisés dans le secteur de la construction, principalement en raison de leur grande capacité d’absorption d’eau. Ces matériaux sont en effet composés de granulats naturels concassés et de pâte de ciment durcie adhérente qui possède une forte porosité. La première partie de ce travail de recherche s’intéresse à la valorisation des GBR de dimensions inférieures à 4 mm (sables recyclés) dans une formulation de mortier. Les comportements à l’état frais et durci de mortiers fabriqués soit avec un sable recyclé soit avec un sable naturel modèle sont comparés. Le sable naturel modèle est conçu dans le but d’obtenir des caractéristiques physiques proches de celles du sable recyclé. Cette démarche permet de mettre en évidence l’influence de la substitution d’un sable naturel par un sable recyclé de caractéristiques voisines. La seconde partie de ce travail consiste à trouver une piste de valorisation pour les particules de GBR inférieures à 125 µm. L’objectif est ici d’utiliser la poudre issue du broyage de GBR comme addition minérale. Un travail de caractérisation de la poudre recyclée permet de mettre en évidence que la fine recyclée reste poreuse après broyage. Un modèle théorique et une méthodologie expérimentale permettant d’estimer cette porosité sont développés. Enfin, des mortiers fabriqués avec un filler calcaire et une fine recyclée sont comparés, les résultats montrent que la fine recyclée peut être utilisée comme addition minéraleRecycled concrete aggregates (RCA) are not enough used in the construction sector, mainly because of their high water absorption capacity. These fine particles are composed of crushed natural aggregate and adherent hardened cement paste. The first part of this work consists in valuing particles smaller than 4 mm of an RCA in a mortar composition. Thus, the fresh and hardened behavior of mortar performed with recycled fine aggregate and model natural aggregate have been compared. The natural model fine aggregate has been performed to have an equivalent physical characteristics with the recycled one. This approach helped to understand the hardened behavior of the mortar made with recycled fine aggregate. The second part of this work consists in finding a recovery track for particles smaller than 125 μm of RCA, the goal is to use them as mineral addition. A characterization work show that the recycled powder is porous, thus a theoretical model and an experimental methodology allowing to estimate this porosity are developed. Finally, a comparison between mortar made with a limestone powder, and a recycled powder are compared. The results show that the recycled powder can be used as mineral additive in mortar composition
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OUALI, ABDELLAH. "Etude experimentale du lessivage des alcalins et du silicium extractibles des granulats naturels apport au probleme de l'alcali-reaction dans les betons". Paris 6, 1997. http://www.theses.fr/1997PA066491.
Testo completoAbstract (sommario):
La determination des alcalins et silice extractibles des granulats a ete mis en uvre dans des reacteurs en inox en systeme semi-ouvert a des temperatures de 20 et 60c. Chaque essai a ete realise a partir de 120 grammes de roches (0,08-0,63 mm) places dans 500 ml de solution de potasse ou de soude a 0,7 m pendant 1000h. Pour se rapprocher du volume de la solution interstitielle du beton, nous avons reduit progressivement le volume de la solution d'attaque a 360, 240 et 120 ml. Les roches selectionnees pour ces experimentations sont : calcaire, pegmatite, granite, rhyolite, basalte, quartzite, amphibolite et gneiss. Les courbes de lessivage s'approchent pour la majorite des roches d'une asymptote a partir de 200h. Nous pouvons considerer qu'a ce stade la majorite des alcalins et de silice susceptibles d'etre extraits est passee en solution. Neanmoins, la dissolution de ces roches est incongruente et non-stchiometrique. Une partie des alcalins et du silicium participe a des nucleations de phases solides ainsi la quantite des elements actifs peut etre legerement sous-estimee. De meme, il n'existe pas de relation nette entre les concentrations des elements passant en solution et le rapport solution/solide (r). Pour r=1, nous avons constate pour la plupart des granulats que la concentration des elements en solution augmente en meme temps que la quantite de produits neoformes. L'etude petrologique et les resultats experimentaux de lessivage montrent une correlation entre la quantite d'alcalins extraits, la teneur totale initiale des roches et leur composition mineralogique. Cependant, pour determiner la reactivite d'un materiau vis-a-vis de l'alcali-reaction, il faut prendre en consideration a la fois la reactivite siliceuse et alcaline du granulats. Si on se base a la fois sur les alcalins et la silice lessivees, nous pouvons distinguer des roches non actives, alcali-actives (pegmatite et amphibolite), silico-actives (calcaire et quartzite) et silico-alcali-actives (gneiss, rhyolite, granite et basalte). L'utilisation des roches a potentialites alcali-siliceuses importantes exigera le choix d'un ciment peu alcalin pour la realisation des ouvrages ou le risque d'alcali-reaction ne peut etre tolere. Par contre, l'utilisation des granulats peu actifs vis-a-vis des alcalins permettra des choix plus large de ciment.
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Mnif, Ines. "Devenir des floculants à base de polyacrylamide dans un site de granulat : interactions avec les solides naturels et photodégradation". Thesis, Nice, 2015. http://www.theses.fr/2015NICE4032/document.
Testo completoAbstract (sommario):
Les floculants à base de polyacrylamide (PAM) sont produits à partir du monomère toxique : l’acrylamide (AMD) et peuvent en contenir des quantités résiduelles (jusqu’à 0,1% en Europe). Après utilisation pour faciliter la séparation solide/liquide des eaux de procédés dans les industries de granulat, ces floculants sont stockés avec les boues de décantation dans des lagunes à partir desquelles une dissémination de l’AMD et du PAM vers les eaux de surface ou les eaux souterraines peut avoir lieu. Dans ces travaux de thèse, les interactions du PAM et de l’AMD avec des particules de boue et des phases argileuses (kaolinite et illite, utilisées pour étanchéifier les lagunes de décantation) ont été étudiées. Pour pouvoir quantifier correctement l’AMD, une méthode d’analyse basée sur la HPLC/MS/MS en injection directe a été développée. Cette méthode a été validée avec les normes Afnor NF T 90-210 et NF T 90-220 avec une limite de quantification égale à 1 µg/L. L’étude de l’interaction de l’AMD avec des particules de boue d’un site de granulat et deux argiles (kaolinite et illite) a mis en évidence une faible adsorption de l’AMD sur ces phases solides (<10%), indépendante du temps, de la concentration en AMD et du pH. Inversement, le PAM s’adsorbe fortement et irréversiblement sur la boue, la kaolinite et l’illite avec une cinétique rapide de 1er ordre. Les isothermes d’adsorption sont bien corrélées avec les modèles de Langmuir et de Freundlich. Les quantités d’adsorption du PAM sont indépendantes du pH des suspensions mais fortement impactées par la force ionique qui influence les interactions électrostatiques entre le PAM et les surfaces solidesPolyacrylamide (PAM) based floculants are produced from the highly toxic acrylamide (AMD) monomer and can contain residual amounts (up to 0.1% in Europe) of AMD. After they are used to facilitate liquid/solid separation of process water in aggregate quarries, PAM floculants are stored, with the sewage sludge, in decantation lagoons. Dissemination of AMD and PAM to groundwater and surface water from these lagoons can occur. In this work, we aimed to study the interactions of AMD and PAM with sludge particles and clays (kaolinite and illite used for decantation lagoon sealing) from aggregate quarry. To correctly quantify the AMD, analytical method based on HPLC/MS/MS with direct injection was developed. This method was validated according to the Afnor guidelines (NF T 90-210 and NF T 90-220) with a limit of quantification of 1 µg/L. Results of AMD adsorption experiments showed a low adsorption of AMD to sludge and clay (kaolinite and illite) particles, which is independent of time, AMD concentration and pH. Inversely, PAM was found to adsorb strongly and irreversibly to sludge, kaolinite and illite with a rapid kinetic of adsorption which consists of first order kinetic. Adsorption isotherms are well correlated with Langmuir and Freundlich models. PAM adsorption quantities are independent on the pH of suspensions, but are strongly impacted by the ionic strength which affects electrostatic interactions between PAM and solid surfaces
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Themeli, Andrea. "Etude du potentiel d'emploi des bitumes naturels dans la production des liants bitumineux durs et des enrobés à module élevé". Thesis, Strasbourg, 2015. http://www.theses.fr/2015STRAD020.
Testo completoAbstract (sommario):
Le but de ce travail est d’étudier le potentiel d’un bitume naturel (BN) extrait en Albanie pour la production des bitumes durs (BD) et des enrobés à module élevé (EME). Pour la production des BD, différentes techniques de raffinage du pétrole existent. Néanmoins, avec certains bruts pétroliers il est impossible de les fabriquer. De plus, les BD de raffinerie comportent souvent des défauts qui limitent leurs applications. Ces raisons, couplées à des questions d’approvisionnement, conduisent à chercher des méthodes de substitution. Dans ce contexte, il est intéressant d’utiliser des BN. Cette étude a montré que le BN d’Albanie donne des BD et des EME en conformité avec la Normalisation Européenne, résistants au vieillissement et performants aux basses températures. Un dosage adéquat permet de formuler des matériaux d’une dureté désirée en réponse des exigences techniques des applications routières visées tout en facilitant la gestion des stocks de bitumes dans les centrales d’enrobagesThe aim of this thesis is to study the potential of a natural bitumen (NB) mined in Albania in the production of hard bitumens (HB) and that of high modulus asphalt concrete (HMAC). Various petroleum refining techniques are available for the production of HB. Nevertheless, this is impossible with some crude oils. In addition, HB from refineries often present shortcomings which limit their applications. These reasons, coupled with practical issues related to HB supply, motivate the research of alternative methods. In this industrial context it is interesting to use NB. This study has shown that the Albanian NB provides HB and HMAC in accordance with European Standards, resistant to aging and relatively performant at low temperatures. The proper dosage of this NB allows the formulation of materials of desired properties, in response to the technical requirements of the considered road applications, facilitating in this way the use of bitumen stocks in asphalt concrete production plants
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Achour, Taoufik. "Étude de l’influence de la nature des granulats sur les propriétés des bétons hydrauliques : cas des granulats calcaires tunisiens". Thesis, Nancy 1, 2007. http://www.theses.fr/2007NAN10105/document.
Testo completoAbstract (sommario):
Ce travail de thèse s’intéresse à la valorisation des ressources granulaires tunisiennes, de type calcaire, dans les mélanges hydrauliques. Les matériaux utilisés sont issus des carrières de Aïn Tebournouk, Nahli, Jbel Ressas, El Haoureb, Jradou et Tahent qui sont appelées à alimenter les principaux centres de consommation de la région de Tunis et de la zone côtière du Centre-Est. Les propriétés analysées sont les résistances en compression et en traction et le module d’élasticité. Les récents modèles du LCPC français ont été utilisés pour prédire ces propriétés. Ils ne donnent pas toujours des résultats satisfaisants, en particulier si les mélanges sont riches en éléments fins, comme c’est souvent le cas avec des granulats issus de carrières. Les mortiers, micro-bétons et bétons réalisés dans le cadre de ce travail ont permis de proposer une extension de ces modèles. Pour la résistance à la compression, le coefficient d’adhérence a été associé à la teneur en fillers des granulats. L’hypothèse est que la présence des éléments fins, de même nature que les granulats, améliore l’adhérence pâte-granulat, grâce au rapprochement des propriétés de rigidité des deux matériaux. Pour la résistance à la traction, un modèle décrit par une loi hyperbolique a permis d’apporter une interprétation physique au comportement à la traction des mélanges hydrauliques. Ses paramètres sont reliés à la résistance du granulat et à la cohésion dans la zone de transition pâte-granulat. Enfin pour le module d’élasticité, l’utilisation du modèle du LCPC, qui prend en compte les propriétés de la phase granulaire et de la phase liante, a permis d’atteindre le module d’élasticité de certains granulatsThis study concerns the Tunisian granular resources, of limestone type, in the hydraulic mixtures. The used materials outcoming from the careers of Aïn Tebournouk, Nahli, Jbel Ressas, El Haoureb, Jradou and Tahent which have to feed the principal centers of consumption of the area of Tunis and the coastal zone of Center-East. The analyzed properties are the compressive and the tensile strengths and the elastic modulus. The recent models of the French LCPC were used to predict these properties. They do not always give satisfactory results, in particular if the mixtures are rich in fine elements, as it is often the case of the aggregates outcoming from careers. The mortars, micro-concretes and concretes carried out within the framework of this study made it possible to propose an extension of these models. For the compressive strength, the bond coefficient was associated with the content of fillers aggregates. The assumption is that the presence of these fine elements, of comparable nature that the aggregates, improves adherence paste and aggregate, thanks to bringing together the properties of rigidity of the two materials. For the tensile strength, a model describes by a hyperbolic law made it possible to provide a physical interpretation to the tensile strength behavior of the hydraulic mixtures. Its parameters are linked to the aggregate strength and cohesion in the paste-aggregate transition zone. Finally for the elastic modulus, the use of the model of the LCPC, which takes into account the properties of the granular phase and the binding phase, made it possible to reach the modulus of elasticity of some aggregates
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Motta, Rafael Gonçalves da. "Evolução tectono-metamórfica do Domínio Serra da Natureza, Terreno Andrelândia, MG". Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/44/44143/tde-23112009-091116/.
Testo completoAbstract (sommario):
O Terreno Andrelândia está localizado na porção sul da Faixa Brasília, é composto por pilha predominantemente metassedimentar, que foi submetida a metamorfismo de pressões relativamente altas durante o Neoproterozóico. Na área investigada o Terreno Andrelândia é formado, da base para o topo, pelas nappes Andrelândia e Liberdade e pela klippe Serra da Natureza, as duas últimas pertencem ao Domínio Serra da Natureza. O presente trabalho tem por objetivo a caracterização geológica, estrutural e petrológica das rochas da Klippe Serra da Natureza e seu contexto no Sistema de Nappes Andrelândia. Na Nappe Andrelândia ocorrem dois litotipos principais: o Xisto Santo Antônio e o Xisto Serra da Boa Vista. Dentro da estrutura são observadas paragêneses a estaurolita-cianita-biotita, no lado oeste da área, e a cianita-biotita-granada, no lado leste, padrão que configura caráter invertido do metamorfismo, com rochas de temperaturas mais elevadas no topo da estrutura. Cálculos geotermobarométricos indicam condições P-T de 668±15 ºC e 9,1±0,7 kbar, para a porção oeste, e 665±17 ºC e 10,4±0,7 kbar, para a porção leste. A Nappe Liberdade é composta por rochas metassedimentares com raras intercalações de anfibolito e rochas metaultramáficas. Na base ocorrem paragnaisses migmatíticos que transicionam para xistos com estaurolita, no topo, configuração que caracteriza metamorfismo de caráter normal. Cálculos geotermobarométricos indicam condições P-T de 714±29 ºC e 10,2±1 kbar, para a base, 678±60 ºC e 8,4±1,3 kbar, para a porção intermediária e 642±28 ºC e 8,2 kbar, para o topo, corroborando com as observações de campo do padrão metamórfico. Esta é a primeira caracterização detalhada das rochas da Klippe Serra da Natureza, formada por paragnaisse granulítico, com leucossoma contendo granada e cianita, e mesossoma com a paragênese, característica da fácies granulito de alta pressão, rutilo + ortoclásio + cianita + granada + quartzo ± plagioclásio ± biotita, sem muscovita e estaurolita. Cálculos termobarométricos em duas amostras da klippe indicam condições P-T de 815 ºC e 15 kbar. As trajetórias P-T inferidas para as rochas dos três alóctones são coerentes e paralelas, as feições retrometamórficas são mais evidentes nas rochas da Nappe Liberdade e da Klippe Serra da Natureza, sendo que na primeira há substituição de cianita por muscovita + estaurolita, rutilo por ilmenta; nos paragnaisses granulíticos da Klippe Serra da Natureza cianita é substituída por sillimanita, ou sillimanita + biotita±muscovita, ou ainda por muscovita + estaurolita, rutilo é substituído por ilmenita + zircão, granada por biotita + quartzo + feldspatos ± sillimanita e; ortoclásio por muscovita. Com os dados geotermobarométricos e as observações petrográficas estima-se taxa de exumação inicial para as rochas da klippe em torno de 5 kbar/50 ºC. O conjunto das três nappes é articulado pela foliação S2, a foliação principal que é paralela nas três estruturas. S1 é observada nas rochas da nappes Andrelândia e Liberdade em dobras intrafoliais com S2 em posição plano axial e ocorre paralela ao bandamento composicional. S3 é desenvolvida localmente. Dobras D4 e D5 são abertas, de grande amplitude e responsáveis pela acomodação do Domínio Serra da Natureza em calha sinformal, configurando padrão de interferência em domos e bacias. As lineações associadas a indicadores cinemáticos, como porfiroclastos e boudins assimétricos, pares SC e vergência de dobras D2, apontam direção de transporte para NNE. Uma segunda família de lineações de estiramento mineral indica transporte de topo para NW, estando associado ao rompimento de dobras D3. Foram datados grãos de monazita com a microssonda eletrônica. Na Nappe Liberdade foram obtidas datações de 622±6 Ma representativas da idade do pico metamórfico. Na Klippe Serra da Natureza datações de 616±16 Ma são representativas do pico metamórfico e valores de 602±7 Ma, obtidos em grãos da matriz, são interpretadas como idade do retrometamorfismo, implicando em taxa de resfriamento entre 7 e 9 ºC/Ma. Na Nappe Andrelândia, a datação obtida de 586±10 Ma é correlacionável à idade de corpos de leucogranito intrusivos e são interpretadas como idade da progressão do Domínio Serra da Natureza sobre a Nappe Andrelândia. Apesar das diferentes histórias metamórficas das rochas da região, todas as estruturas apresentam relações que permitem incluí-las em único evento metamórfico, com gradiente metamórfico de campo semelhante ao das rochas dos Altos Himalaias, ou seja, em regime de alta pressão e temperatura reinante na crosta inferior de ambiente colisional envolvendo blocos continentais.The Andrelândia Terrain is located in the southern portion of the Brasília Fold Belt and it comprises metasedimentary pile that underwent relative high-pressure metamorphism during the Neoproterozoic. In the investigated area, the Andrelândia Terrain is composed, from bottom to top, by the Andrelândia and Liberdade nappes and the Serra da Natureza Klippe, and the last two belong to the Serra da Natureza Domain. The present work aims the characterization of geology, structure and petrology of rocks of the Serra da Natureza klippe and its context in relation to the Andrelândia Terrain. In the Andrelândia Nappe two kinds of lithotypes occur: the Santo Antônio Schist and Serra da Boa Vista Schist. Inside the nappe, rocks bearing staurolite-kyanite-biotite mineral assemblage are topped by rocks with kyanite-biotite-garnet, characterizing an inverted metamorphic pattern. Geothermobarometric calculating estimates P-T condition of 668±15 ºC and 9.1±0.7 kbar for rocks at the bottom and 665±17 ºC and 10.4±0.7 kbar for rocks at the top. The Liberdade Nappe is composed of metasedimentary rocks, with rare intercalations of amphibolite and metaultramafic rocks. At its base a migmatitic paragneiss dominates and a transition to schists with staurolite-kyanite occurs, at the top of structure, in a normal metamorphic pattern. P-T calculations yielded 714±29 ºC and 10.2±1 kbar to rocks at the base, 678±60 ºC and 8.4±1.3 kbar to rocks of middle portion, and 642±28 ºC and 8.2 kbar to rocks of upper part. It is the first detailed characterization of Serra da Natureza Klippe rocks, which is composed of granulitic paragneiss, in which leucosome-rearing garnet and kyanite are observed along with rutile-orthoclase-kyanite-garnet-quartz±plagioclase±biotite mesosome, without muscovite and staurolite. Thermobarometry in two samples yielded P-T conditions of 815 ºC and 15 kbar. The P-T paths inferred for rocks of the three units are consistent and parallel, and features related to retrometamorphism are recorded more intensively in rocks of the Liberdade Nappe and Serra da Natureza Klippe. In the first, replacement of kyanite by muscovite + staurolite and rutile by ilmenite are common; in the Serra da Natureza Klippe, there is replacement of kyanite either by sillimanite, or sillimanite + biotite ± muscovite, or muscovite + staurolite, rutile by ilmenite + zircon, garnet by biotite + quartz + feldspars ± sillimanite; and of orthoclase by muscovite. These observations give the initial exhumation rate of 5 kbar/50 ºC. All the three nappes are linked by S2, which is the main and parallel foliation in all of them. S1 is observed in the Andrelândia and Liberdade nappes, defining fold hinges that have S2 in axial plane position and is parallel to S0. S3 is locally developed. Late D4 and D5 deformation are responsible for large amplitude open folds, to the synform of Serra da Natureza Domain, as well as regional dome and basin interference pattern. Mineral and stretching lineations are associated with kinematic indicators, such as porphyroclast, asymmetric boundins, SC foliation and vergence of folds (D2), indicate transport to NNE. A second family of mineral and stretch lineations indicates transport to NW, associated with the disruption of D3 folds. Monazite grains have been dated by electron microprobe (EPMA). In the Liberdade Nappe, value of 622±6 Ma was obtained and is interpreted as the age of metamorphic peak. In the Serra da Natureza Klippe, a date of 616±16 Ma represents the age of metamorphic peak and the value of 602±7 Ma is interpreted as age of retrometamorphism, implying a cooling rate between 7 and 9 ºC/Ma. In the Andrelândia Nappe monazite dating yielded 586±10 Ma, what is correlated to the age of leucogranite intrusions and is interpreted as age of the progression of de Serra da Natureza Domain over the Andrelândia Nappe. Although the investigated rocks present different metamorphic stories, all of them, and their major structures, are connected by a single tectono-metamorphic event, with a high pressure and temperature metamorphic field gradient, which is similar to the rocks of High Himalayan, and typical of lower crust in collisional setting involving continental blocks.
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Achour, Taoufik Lecomte André Ben Ouezdou Mongi. "Étude de l'influence de la nature des granulats sur les propriétés des bétons hydrauliques cas des granulats calcaires tunisiens /". S. l. : S. l. : Nancy 1 ; Ecole National d'Ingénieurs de Tunis, 2007. http://www.scd.uhp-nancy.fr/docnum/SCD_T_2007_0105_ACHOUR.pdf.
Testo completoAbstract (sommario):
Thèse de doctorat : Génie Civil : Nancy 1 : 2007. Thèse de doctorat : Génie Civil : Ecole National d'Ingénieurs de Tunis : 2007.Thèse soutenue en co-tutelle. Titre provenant de l'écran-titre. Bibliogr.
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Liu, Mingzhao. "Decouplage des systemes avec retards : simulation et commande optimale d'une installation de production des granulats". Nantes, 1988. http://www.theses.fr/1988NANT2041.
Testo completoAbstract (sommario):
Synthese de la theorie du decouplage des systemes avec retard, a l'aide d'un operateur de retard (compensateur dynamique pour fixer les coefficients du polynome caracteristique). Algorithme de commande optimale d'une installation de concassage, en deux niveaux: optimisation statique (maximisation de la production et/ou minimisation de la consommation electrique); regulation autour du point nominal, par modeles linearises, utilisant aussi les regulateurs de smith. Correction des erreurs dues a l'usure des concasseurs. Resultats en simulation et sur site
Libri sul tema "Granulats naturels"
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service), SpringerLink (Online, a cura di. Soft Matter: The stuff that dreams are made of. Dordrecht: Springer Science+Business Media B.V., 2011.
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Fellerer, Jan. Theories of Language. A cura di Paul Hamilton. Oxford University Press, 2016. http://dx.doi.org/10.1093/oxfordhb/9780199696383.013.40.
Testo completoAbstract (sommario):
This chapter identifies key notions about the nature and workings of language and their wider political implications in Europe from around 1789 to the first decades of the nineteenth century. There are at least three formations, aesthetic and philosophical, linguistic, and political. Even though treated under separate headings for ease of exposition, they are meant to meet in this introduction in response to more granular surveys. The political dimension in particular tends to be left to historians or to philologists who deal with that part of the continent where it first gained real prominence: East and East Central Europe. Thus, after the first two sections on aspects of philosophy and early linguistics, where the focus is on Germany with France and England, the third section on language and nation moves eastwards to the Slavonic-speaking lands, to finally return back, albeit very briefly, to the West. The main purpose of this survey to provide introduction and guidance.
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Zapperi, Stefano. Crackling Noise. Oxford University PressOxford, 2022. http://dx.doi.org/10.1093/oso/9780192856951.001.0001.
Testo completoAbstract (sommario):
Abstract Crackling noise refers to an intermittent series of pulses of broadly distributed amplitude and duration that is observed in different contexts from the crumpling of a sheet of paper to the flow of fluids in porous media. Studying crackling noise is interesting because it reflects key microscopic processes inside the material, with each crackle in the noise corresponding to an internal avalanche event. A distinct statistical feature of crackling noise is the presence of power law distributed noise pulses and long-range correlations which are the hallmarks of critical phenomena. Hence, the physics of complex non-equilibrium disordered systems provides the natural theoretical framework to tackle crackling noise. The present book reviews the statistical properties of crackling noise, providing an introduction to the main theoretical concepts needed to interpret them. The book also contains a detailed discussion of several examples of crackling noise in materials, including fracture, plasticity, ferromagnetism, superconductivity, granular flow and fluid flow in porous media. A final chapter discusses the relevance of avalanche behavior for biological systems.
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Okay, Oguz. Polymeric Cryogels: Macroporous Gels with Remarkable Properties. Springer London, Limited, 2014.
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Okay, Oguz. Polymeric Cryogels: Macroporous Gels with Remarkable Properties. Springer, 2016.
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Polymeric Cryogels: Macroporous Gels with Remarkable Properties. Springer International Publishing AG, 2014.
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Pujala, Ravi Kumar. Dispersion Stability, Microstructure and Phase Transition of Anisotropic Nanodiscs. Springer, 2016.
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Pujala, Ravi Kumar. Dispersion Stability, Microstructure and Phase Transition of Anisotropic Nanodiscs. Springer London, Limited, 2014.
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Dispersion Stability, Microstructure and Phase Transition of Anisotropic Nanodiscs. Springer, 2014.
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La Materia Dei Sogni Sbirciatina Su Un Mondo Di Cose Soffici Lettore Compreso. Springer, 2010.
Cerca il testo completoCapitoli di libri sul tema "Granulats naturels"
1
Artiemjew, Piotr. "Natural versus Granular Computing: Classifiers from Granular Structures". In Rough Sets and Current Trends in Computing, 150–59. Berlin, Heidelberg: Springer Berlin Heidelberg, 2008. http://dx.doi.org/10.1007/978-3-540-88425-5_16.
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Glöckner, Ingo, e Alois Knoll. "A Formal Theory of Fuzzy Natural Language Quantification and its Role in Granular Computing". In Granular Computing, 215–56. Heidelberg: Physica-Verlag HD, 2001. http://dx.doi.org/10.1007/978-3-7908-1823-9_10.
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Jiang, Yimin, e Mario Liu. "The Physics of Granular Mechanics". In Mechanics of Natural Solids, 27–46. Berlin, Heidelberg: Springer Berlin Heidelberg, 2009. http://dx.doi.org/10.1007/978-3-642-03578-4_2.
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Jankowski, Andrzej, e Andrzej Skowron. "Wisdom Technology: A Rough-Granular Approach". In Aspects of Natural Language Processing, 3–41. Berlin, Heidelberg: Springer Berlin Heidelberg, 2009. http://dx.doi.org/10.1007/978-3-642-04735-0_1.
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Santamarina, J. Carlos, e Hosung Shin. "Discontinuities in granular materials: Particle-level mechanisms". In Mechanics of Natural Solids, 223–37. Berlin, Heidelberg: Springer Berlin Heidelberg, 2009. http://dx.doi.org/10.1007/978-3-642-03578-4_10.
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Amorosi, A., e M. J. Kavvadas. "A plasticity-based constitutive model for natural soils: a hierarchical approach". In Constitutive Modelling of Granular Materials, 413–38. Berlin, Heidelberg: Springer Berlin Heidelberg, 2000. http://dx.doi.org/10.1007/978-3-642-57018-6_20.
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Ortaldo, John R. "Cytokine Production by CD3¯ Large Granular Lymphocytes". In Functions of the Natural Immune System, 299–318. Boston, MA: Springer US, 1989. http://dx.doi.org/10.1007/978-1-4613-0715-0_13.
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Kozlov, Valery V., Boris N. Chetverushkin, Alexander P. Buslaev, Alexander G. Tatashev e Marina V. Yashina. "Algebraic and Geometric Aspects of Flow Modeling and Prospects of Natural Science Applications". In Traffic and Granular Flow '17, 433–42. Cham: Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-030-11440-4_47.
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Alonso, E. E., L. Oldecop e N. M. Pinyol. "Long term behaviour and size effects of coarse granular media". In Mechanics of Natural Solids, 255–81. Berlin, Heidelberg: Springer Berlin Heidelberg, 2009. http://dx.doi.org/10.1007/978-3-642-03578-4_12.
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Hoffmann, K., M. Huculak-Mączka e J. Hoffmann. "Granulated Mineral-Organic Humic Preparations Based on PAPR". In Functions of Natural Organic Matter in Changing Environment, 1133–36. Dordrecht: Springer Netherlands, 2012. http://dx.doi.org/10.1007/978-94-007-5634-2_210.
Testo completoAtti di convegni sul tema "Granulats naturels"
1
JASINSKAS, Algirdas, Ramūnas MIELDAŽYS, Juozas PEKARSKAS, Sigitas ČEKANAUSKAS, Antonin MACHALEK e Jiri SOUČEK. "THE ASSESSMENT OF ORGANIC AND NATURAL MAGNESIUM MINERAL FERTILIZERS GRANULATION AND THE DETERMINATION OF PRODUCED PELLET PROPERTIES". In RURAL DEVELOPMENT. Aleksandras Stulginskis University, 2018. http://dx.doi.org/10.15544/rd.2017.040.
Testo completoAbstract (sommario):
The research was carried out in Aleksandras Stulginskis University with a natural magnesium mineral fertilizer – magnesium silicate Serpentine rocks that were grounded and granulated with an impact granulation technology, organic cattle manure compost fertilizer, which was granulated using a device with a horizontal granulator matrix (the diameter of pellets is 6 mm), and the mixture of Serpentine and manure pellets (mixture ratio 1:1, diameter of pellets is6 mm). There were investigated and estimated the biometric and physical-mechanical properties of produced fertilizer granules – pellet granulometric composition and biometric indicators, moisture content, density and pellet strength (resistance to impact forces). Research results showed that the pellet moisture content was sufficiently low, varied from 4.7 % to 14.7 %, and the density of produced pellet was considerably high as it reached more than 1000 kg m-3 DM (dry matter). Results on resistance to the deformation of the investigated mineral magnesium and organic fertilizers indicate that the most resistant granules are the ones that are made of the mixture of Serpentine and manure pellets as they decompose to 550.5 N force, whereas granules of manure pellets (without Serpentine) disintegrate to a 271.4 N force, which is about twice as small as the above mentioned one. Research results have shown that fertilizer granules made of organic manure and mixture with magnesium silicate Serpentine are of high quality, these granules are sufficiently resistant to compression on a static force as well as convenient for storage, transportation and mechanical spreading in the field.
2
Fang, X., H. Luo e J. Tang. "Analysis of Granular Damping Using Hilbert Transform Based Technique". In ASME 2007 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. ASMEDC, 2007. http://dx.doi.org/10.1115/detc2007-34900.
Testo completoAbstract (sommario):
Granular damping results from a combination of energy dissipation mechanisms including the impact and the friction between the vibrating structure and granules and among the granules. Although simple in concept, granular damping is very complicated and its performance depends on a number of factors, such as vibration level, granular material properties, and packing ratio, etc. In this study, free vibration tests are conducted on a cantilevered beam incorporated with granular damping. A signal analysis approach based on the Hilbert transform (HT) is then employed to identify the nonlinear damping characteristics from the acquired responses, such as the dependency of the natural frequency and damping ratio on vibration level. This HT based analysis can produce an accurate temporal-frequency amplitude/energy analysis which provides us with physical insights of the nonlinear transient response. A direct comparison between the granular damping and the impact damping (with single impactor to dissipate vibratory energy) is performed to highlight the difference between these two as well as the advantages of granular damping. Finally, validity of the proposed approach is also examined by the successful prediction of vibration response using the extracted granular damping characteristics.
3
Kabir, M. A., C. Fred Higgs e Michael R. Lovell. "Granular Flow Modeling and Simulation Using a Dynamic Finite Element Method". In ASME/STLE 2007 International Joint Tribology Conference. ASMEDC, 2007. http://dx.doi.org/10.1115/ijtc2007-44313.
Testo completoAbstract (sommario):
Granular flow behavior is of fundamental interest to the engineering and scientific community because of the prevalence of these flows in the pharmaceutical, agricultural, food service, and powder manufacturing industries. Granular materials exhibit very complex behavior, oftentimes acting as solids and at other times as fluids. This dual nature leads to very complex and rich behavior, which is not yet well understood. Therefore, the present investigation introduces a new technique that can potentially be used to unveil the mystery of granular flow phenomena. To this end, advanced finite element modeling and simulation techniques have been applied to the study of the complex nature of granular flow. More specifically, the explicit dynamic code LS-DYNA has been utilized to gain an understanding of the complex flow nature and collision stresses of granules in a shear cell.
4
Houlihan, Ryan, e Rudranarayan Mukherjee. "Massively Parallel Discrete Element Modeling of Wheeled Mobility on Granular Terrain". In ASME 2013 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/detc2013-13318.
Testo completoAbstract (sommario):
Quantitatively understanding wheeled mobility on granular terrain such as sand or gravel is critical for design and operations of ground vehicles for terrestrial or extra-terrestrial applications. While the Bekker-Wong theory of wheeled mobility and its derivatives have been used in many applications, the static nature of these formulations are limiting in understanding mobility in deformable terrain under dynamic mobility conditions. Single wheel hardware experiments in laboratory settings and detailed modeling of wheel-terrain interactions are two avenues currently being actively pursued to develop quantitative understanding of wheeled mobility. In this paper, we present findings of massively parallel discrete element modeling of wheeled mobility on granular media such as sand. We present a brief overview of the underlying methodology and then focus on the results of the simulation. In these simulations, we model the inter-granular interactions and interactions between the wheel and the granules with an objective of using high fidelity first-principles approach to capture emergent behavior in these complex and highly dynamic phenomena. These simulations typically model millions of granules and use highly scalable software and parallel computing resources to overcome the severe complexity of the problem. We present results of parametric studies with varying levels of both wheel penetration and mobility conditions. These have been modeled to present a quantitative perspective of the diverse behaviors encountered in wheeled mobility on granular terrain. We have retained the full complexity of the problem by simulating granules of the size encountered in real terrain to overcome the fidelity limited issues of other comparable methods that use much larger granules.
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Kruggel-Emden, Harald, Siegmar Wirtz e Viktor Scherer. "Selection of Optimal Models for the Discrete Element Method: The Single Particle Perspective". In ASME 2008 Pressure Vessels and Piping Conference. ASMEDC, 2008. http://dx.doi.org/10.1115/pvp2008-61042.
Testo completoAbstract (sommario):
Several processes in nature as well as many industrial applications involve static or dynamic granular materials. Granulates can adopt solid, liquid or gas like states and thereby reveal intriguing physical phenomena not observable in its versatility for any other form of matter. The frequent occurrence of phase transitions and the related characteristics thereby strongly affect their processing quality and economics. This situation demands for prediction methods for the behavior of granulates. In this context simulations provide a feasible alternative to experimental investigations. Several different simulation approaches are applicable to granular materials. The time-driven Discrete Element Method turns out to be the most complex but also as the most general method. The method has been used in a wide variety of scientific fields for more than thirty years. With the tremendous increase in available computer power, especially in the last years, the method is more and more developing to the state of the art simulation technique for granular materials. Despite of the long time of usage, model advances and theoretical and experimental studies are not harmonized in the different branches of application, providing potential for improvements. Therefore, the scope of this paper is a review of methods and models based on theoretical considerations and experimental data from literature. Through model advances it is intended to contribute to a general enhancement of techniques, which are then directly available for simulations.
6
Kumar, Pankaj. "Optimizing Sulphur Granulation Process Scheme to Reduce System CAPEX". In ADIPEC. SPE, 2023. http://dx.doi.org/10.2118/216462-ms.
Testo completoAbstract (sommario):
Abstract Sulphur is a vital and essential by-product of sour gas processing. Smooth operation of Sulphur production/ handling facilities is a key for business continuity in gas processing industry. Sulphur (Solid) is a challenging material to handle due to its brittle nature and prone to breakage due to abrasion during transport, storage, and handling. Excessive dust generation poses a serious safety risk due to explosive nature of Sulphur dust. Despite various measures to collect and suppress Sulphur dust, it remains a potential source of fire and explosion hazards, as well as maintenance issues Apart from other forms of Sulphur compound (H2S/SO2/SO3), elemental Sulphur itself in the form of yellow dust is also an environmental pollutant. Sulphur is transported mainly in solid form as liquid Sulphur transportation is a big hazard. This study is based on experience from a Sulphur granulation and handling facility in an organization which produces and handles the liquid /granulated Sulphur at a very large scale with around 22000 TPD. During transport / storage / handling, due to breakage of Sulphur granules, huge dust is generated. Being air-borne, this Sulphur dust has a great potential of fire/explosion and serious HSE concern for organization considering safety as its top priority. Considering above, strength of granulated Sulphur product is of utmost importance. This strength depends on polymeric content in Sulphur. Various old research used to recommend different operating parameters to increase and maintain the polymeric Sulphur content. One of the conventional approaches is to maintain high liquid Sulphur temperature during transportation and storage and cooling in Sulphur coolers just before solidification in granulation process through Granulators. Sulphur coolers and associated system are CAPEX intensive. This paper explores the possibility of eliminating the Sulphur coolers requirement to optimize the CAPEX.
7
Marinack, Martin C., Venkata K. Jasti e C. Fred Higgs. "An Experimental Study of the Effect of Global Solid Fraction and Surface Material on Couette Granular Flow". In ASME/STLE 2009 International Joint Tribology Conference. ASMEDC, 2009. http://dx.doi.org/10.1115/ijtc2009-15143.
Testo completoAbstract (sommario):
The flow of solid granular material has been proposed as an alternative lubricant to conventional liquid lubricants. Since granular flows are also in numerous industrial and natural processes, they have been the subject of numerous studies. However, it has been a challenge to understand them because of their non-linear and multiphase behavior. There have been several past experiments, which have gained insight into granular flows. For example, previous work by the authors sheared grains in a two-dimensional annular shear cell by varying the velocity and roughness [1]. The present experimental work attempts to further insights from the previous work by specifically studying the interaction between rough surfaces and granular flows when the global solid fraction and grain materials are varied. A two dimensional annular (granular) shear cell, with a stationary outer ring and inner driving wheel, was used for this work. Digital particle tracking velocimetry was used to obtain local granular flow data such as velocity, local solid fraction, and granular temperature. Slip between the driving wall and first layer of granules is also extracted. This slip can be interpreted as momentum transfer or traction performance in granular systems such as wheel-terrain interaction. Parametric studies of global solid fraction and the material of the rough driving surface, attempt to show how these parameters affect the local granular flow properties.
8
Mukherjee, Rudranarayan, e Isaac Kim. "Massively Parallel Discrete Element Modeling of Legged Mobility on Granular Terrain". In ASME 2013 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/detc2013-13329.
Testo completoAbstract (sommario):
Legged mobility of robotic systems is an active area of research. Quantitatively understanding mobility of these systems on natural terrain is critical for design and operations of these systems. In this paper, we present results of computational simulations of legged mobility on granular terrain using massively parallel Discrete Element Method. We model the interactions of a leg from a micro ground vehicle with sandy terrain made of polydispersed granular media. In these simulations, we model the interactions between millions of granules and the leg to quantify ground reactions and associated qualitative behaviors. The simulations are run on parallel computers to overcome the severe computational complexity of simulating these large problems in physically feasible time-frames. We are using high fidelity first-principles approaches to model emergent complex behavior that cannot otherwise be modeled. We present results from a parametric sweep where different leg speeds and penetrations are used to understand differences in ground reaction.
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Grosse, Karl-Heinz, Milan Hrovat, Richard Seemann e Robert Feher. "Improvement of Nuclear Grade Graphite Based on Isotropic and Highly Crystalline Natural Graphite by Generation of Silicon- or Zirconium-Carbide in Situ". In Fourth International Topical Meeting on High Temperature Reactor Technology. ASMEDC, 2008. http://dx.doi.org/10.1115/htr2008-58026.
Testo completoAbstract (sommario):
Following the fabrication technique originally developed for HTR-molded block fuel elements a process was introduced to fabricate nuclear graphite with the aim to attain the improved irradiation stability above 3 × 1022n/cm2, E > 0,1 MeV and to increase corrosion resistance. Nuclear highly crystalline natural graphite is used. A phenol formaldehyde resin with additives of silicon or zirconium oxide powder serves as binder. The mixture thus obtained is isostatically consolidated into spheres and spheres are crushed to granules from which the 0.3 – 3 mm fraction is obtained. The granulate is hot molded into graphite bodies. The green bodies are heated to about 800 °C to carbonise the resin and subsequently annealed at 1900°C in vacuum. The key feature of the proposed process is based on the chemical affinity of binder coke with the structure obtained by carbonisation of green bodies. Consequently it reacts selectively in situ with the added SiO2, or ZrO2to carbides in vacuum at 1900°C. Silicon carbides and zirconium carbides are characterised by high mechanical strength and very good resistance to corrosion. The properties of reactor graphite, such as density, mechanical properties and in particular stability to fast neutron irradiation are considerably improved.
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Hu, Hong, e Zhongzhi Shi. "Perception Learning as Granular Computing". In 2008 Fourth International Conference on Natural Computation. IEEE, 2008. http://dx.doi.org/10.1109/icnc.2008.895.
Testo completoRapporti di organizzazioni sul tema "Granulats naturels"
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Ben-David, Itzhak, Francesco Franzoni, Rabih Moussawi e John Sedunov. The Granular Nature of Large Institutional Investors. Cambridge, MA: National Bureau of Economic Research, maggio 2016. http://dx.doi.org/10.3386/w22247.
Testo completo
2
Tan, Peng, e Nicholas Sitar. Parallel Level-Set DEM (LS-DEM) Development and Application to the Study of Deformation and Flow of Granular Media. Pacific Earthquake Engineering Research Center, University of California, Berkeley, CA, marzo 2023. http://dx.doi.org/10.55461/kmiz5819.
Testo completoAbstract (sommario):
We present a systematic investigation of computational approaches to the modeling of granular materials. Granular materials are ubiquitous in everyday life and in a variety of engineering and industrial applications. Despite the apparent simplicity of the laws governing particle-scale interactions, predicting the continuum mechanical response of granular materials still poses extraordinary challenges. This is largely due to the complex history dependence resulting from continuous rearrangement of the microstructure of granular material, as well as the mechanical interlocking due to grain morphology and surface roughness. X-Ray Computed Tomography (XRCT) is used to characterize the grain morphology and the fabric of the granular media, naturally deposited sand in this study. The Level-Set based Discrete Element Method (LS-DEM) is then used to bridge the granular behavior gap between the micro and macro scale. The LS-DEM establishes a one-to-one correspondence between granular objects and numerical avatars and captures the details of grain morphology and surface roughness. However, the high-fidelity representation significantly increases the demands on computational resources. To this end a parallel version of LS-DEM is introduced to significantly decrease the computational demands. The code employs a binning algorithm, which reduces the search complexity of contact detection from O(n2) to O(n), and a domain decomposition strategy is used to elicit parallel computing in a memory- and communication-efficient manner. The parallel implementation shows good scalability and efficiency. High fidelity LS avatars obtained from XRCT images of naturally deposited sand are then used to replicate the results of triaxial tests using the new, parallel LS-DEM code. The result show that both micro- and macro-mechanical behavior of natural material is well captured and is consistent with experimental data, confirming experimental observation that the primary source of peak strength of sand is the mechanical interlocking between irregularly shaped grains. Specifically, triaxial test simulations with a flexible membrane produce a very good match to experimentally observed relationships between deviatoric stress and mobilized friction angle for naturally deposited sand. We then explore the viability of modeling dynamic problems with a new formulation of an impulse based LS-DEM. The new formulation is stable, fast, and energy conservative. However, it can be numerically stiff when the assembly has substantial mass differences between particles. We also demonstrate the feasibility of modeling deformable structures in the rigid body framework and propose several enhancements to improve the convergence of collision resolution, including a hybrid time integration scheme to separately handle at rest contacts and dynamic collisions. Finally, we extend the impulse-based LS-DEM to include arbitrarily shaped topographic surfaces and exploit its algorithmic advantages to demonstrate the feasibility of modeling realistic behavior of granular flows. The novel formulation significantly improves performance of dynamic simulations by allowing larger time steps, which is advantageous for observing the full development of physical phenomena such as rock avalanches, which we present as an illustrative example.
3
Tarpley, Danielle, e David Perkey. Impacts of Granular Activated Carbon (GAC) on erosion behavior of muddy sediment. Engineer Research and Development Center (U.S.), luglio 2022. http://dx.doi.org/10.21079/11681/44841.
Testo completoAbstract (sommario):
Recent policy changes regarding the placement of dredged material have encouraged the USACE to increase its beneficial use (BU) of the sediments dredged from the nation’s navigation channels. A good portion of this material is fine grained (<63 μm), which traditionally has limited use in BU applications, in part due to its dispersive nature. A need exists to evaluate the potential of stabilizing and using fine-grained sediment (FGS) in BU projects. Previous studies have shown the addition of granular sand to FGS reduces the mobility of the bed. The potential of using Granular Activated Carbon (GAC), an amendment commonly used in environmental capping involving FGS, as a similar bed stabilizing material was explored in this study. A series of laboratory erosion tests using Sedflume were performed on FGS-GAC mixtures that ranged from 5% to 20% GAC by mass. Results suggested that GAC content ≤10% had no influence on the stability of the bed while GAC content ≥15% appeared to reduce both critical shear stress (τcr) and erosion rate (n). However, when compared to control cores, those without GAC, clear evidence of bed stabilization of FGS from the addition of GAC was not observed.
4
Melcangi, Davide, e Silvia Sarpietro. Nonlinear Firm Dynamics. Federal Reserve Bank of New York, marzo 2024. http://dx.doi.org/10.59576/sr.1088.
Testo completoAbstract (sommario):
This paper presents empirical evidence on the nature of idiosyncratic shocks to firms and discusses its role for firm behavior and aggregate fluctuations. We document that firm-level sales and productivity are hit by heavy-tailed shocks and follow a nonlinear stochastic process, thus departing from the canonical linear. We estimate a state-of-the-art model to flexibly capture the rich dynamics uncovered in the data and characterize the drivers of nonlinear persistence and non-Gaussian shocks. We show that these features are crucial to get empirically plausible volatility and persistence of micro-originated (granular) aggregate fluctuations.
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Breitbarth, Marco, Anja Hentschel e Simon Kaser. Kunststoffeinträge von Kunstrasenplätzen in Entwässerungssystem - Aufkommen, Rahmenbedingungen und Möglichkeiten der Eintragsminderung. Sonderforschungsgruppe Institutionenanalyse, 2022. http://dx.doi.org/10.46850/sofia.9783941627994.
Testo completoAbstract (sommario):
Plastics as an environmental problem have been in the focus of science, politics and the public for a long time. Various sources and pathways have already been identified and a wide range of measures have been developed to reduce and, if possible, avoid inputs into the environment. Artificial grass pitches represent a special source of plastic inputs into the environment. Artificial grass with different infill materials has been widely used for some time now on surfaces for a wide range of sports, both amateur and professional. It is characterised by various advantages over natural grass. However, the use of artificial grass on sports surfaces also has its downsides, especially for the environment. On the one hand, the synthetic grass fibres themselves, which become detached through wear, are problematic. On the other hand, synthetic granulate is used as infill material on these pitches to reduce the risk of injury to players, to support the blades of artificial grass and to improve the playing characteristics of the field. However, this granulate can enter the environment in various ways - indirectly via drainage systems or directly. The following comments reflect research results from the InRePlast project. In the following chapter 2, the results of our own investigations on the topic are presented. In Chapter 3, these are compared to other publications and evaluated with regard to their significance. Chapter 4 is devoted to technical and organisational measures to reduce discharges as well as legal approaches to regulation. Finally, Chapter 5 draws a conclusion. Among other things, the study concludes that artificial grass pitches are less relevant as a specific source of plastic inputs than previously discussed. It should also be noted that the input into drainage systems via the collection of dirty water has a significantly higher relevance than the input via the collection of precipitation at the edge of the pitch and that measures should therefore focus on the carry-over on players' clothing and shoes.
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Palhares Neto, Luiz, Leilane Gomes, José Marangon, Genilton Santos e Cecílio Caldeira Júnior. Protocolo de micropropagação de Cattleya milleri, espécie endêmica do quadrilátero ferrífero criticamente ameaçada de extinção. ITV, maggio 2022. http://dx.doi.org/10.29223/prod.tec.itv.ds.2022.12.palharesneto.
Testo completoAbstract (sommario):
A espécie Cattleya milleri é uma orquídea endêmica dos Campos Rupestres Ferruginosos do Quadrilátero Ferrífero em Minas Gerais. Esta espécie é atualmente classificada como criticamente ameaçada de extinção sobretudo devido a restrição geográfica de sua ocorrência, degradação de seu habitat natural e reduzidas populações naturais. O estabelecimento de métodos de propagação e cultivo que possibilitem a rápida multiplicação desta espécie é etapa crucial para a conservação ex situ e também para o enriquecimento em áreas naturais e a manutenção da espécie em seu habitat. A micropropagação ou a propagação in vitro consiste na multiplicação em larga escala de plantas através do cultivo de células, tecidos, órgãos ou a planta inteira em meio nutritivo sob condições controladas de temperatura e luminosidade. As etapas da micropropagação são constantemente ajustadas de acordo com as necessidades das diferentes espécies. Diante disso, o objetivo do relatório foi descrever as etapas desenvolvidas para estabelecer o protocolo de micropropagação de C. milleri. O protocolo estabelecido foi dividido em quatro etapas: (1) coleta e assepsia do material vegetal, (2) estabelecimento e desenvolvimento in vitro, (3) aclimatização e rustificação e (4) reintrodução e monitoramento das mudas. Sementes de C. milleri foram retiradas de cápsulas maduras e transferidas para seringas. As seringas contendo as sementes foram preenchidas totalmente com a solução de hipoclorito de sódio (NaClO) a 0,3%. Após 12 minutos, em câmara de fluxo laminar, aproximadamente 1 mL da solução contendo as sementes foi adicionada em potes contendo 22 mL do meio de cultivo previamente esterilizado. O meio utilizado foi composto de sacarose (15g/L), fertilizante B&G® (3mL/L), carvão ativado (1,5g/L) e ágar nutriente (5g/L). A germinação foi observada em quase todas as sementes inoculadas, tendo início aos 25 dias. O processo de propagação in vitro de C. milleri teve duração de 18 meses, com dois episódios de repicagem durante esse período. As plantas responderam positivamente as condições in vitro, apresentando crescimento satisfatório da parte aérea e de raízes. Na etapa de aclimatização, as plantas enraizadas tiveram suas raízes lavadas e foram transplantadas para embalagens plásticas contendo musgo chileno e fragmentos de isopor. Após 450 dias de cultivo em estufa coberta com sombrite 80 (80% de interceptação) foi observada uma reduzida mortalidade de mudas. Posteriormente, plantas aclimatadas foram transplantadas para recipientes contendo substrato natural (contendo canga granular) e cultivadas em estufa com sombrite 80 e posteriormente em sombrite 50, onde permaneceram por 1.095 dias. Ao final da etapa de rustificação foram obtidas aproximadamente 3.000 mudas de C. milleri aptas para o plantio em ambiente natural. A reintrodução destas mudas ocorreu através do plantio das mudas na Serra da Calçada (MG). O monitoramento das plantas ocorre mensalmente com a quantificação das mudas sobreviventes. Após 2 anos de acompanhamento observou-se baixa taxa de mortalidade (-30%) e crescimento satisfatório das plantas. O processo de monitoramento continuará sendo realizado com o objetivo de avaliar os processos de floração e frutificação e recrutamento de novas plantas. Os resultados obtidos evidenciam que a técnica de propagação in vitro é uma alternativa viável para a produção em larga escala de mudas de qualidade da espécie C. milleri. Uma vez que esta é uma espécie criticamente ameaçada de extinção, a reintrodução de plantas em ambiente natural contribui para o enriquecimento das populações existentes e, consequentemente, a conservação da espécie em seu ambiente natural. Uma próxima etapa importante será avaliar a diversidade genética da espécie para determinação das matrizes prioritárias para propagação
7
Marcellino, Massimiliano, e Dalibor Stevanovic. The demand and supply of information about inflation. CIRANO, novembre 2022. http://dx.doi.org/10.54932/djgr5759.
Testo completoAbstract (sommario):
In this article we study how the demand and supply of information about inflation affect inflation developments. As a proxy for the demand of information, we extract Google Trends (GT) for keywords such as "inflation", "inflation rate", or "price increase". The rationale is that when agents are more interested about inflation, they should search for information about it, and Google is by now a natural source. As a proxy for the supply of information about inflation, we instead use an indicator based on a (standardized) count of the Wall Street Journal (WSJ) articles containing the word "inflat" in their title. We find that measures of demand (GT) and supply (WSJ) of inflation information have a relevant role to understand and predict actual inflation developments, with the more granular information improving expectation formation, especially so during periods when inflation is very high or low. In particular, the full information rational expectation hypothesis is rejected, suggesting that some informational rigidities exist and are waiting to be exploited. Contrary to the existing evidence, we conclude that the media communication and agents attention do play an important role for aggregate inflation expectations, and this remains valid also when controlling for FED communications.
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Alonso-Robisco, Andrés, José Manuel Carbó e José Manuel Carbó. Machine Learning methods in climate finance: a systematic review. Madrid: Banco de España, febbraio 2023. http://dx.doi.org/10.53479/29594.
Testo completoAbstract (sommario):
Preventing the materialization of climate change is one of the main challenges of our time. The involvement of the financial sector is a fundamental pillar in this task, which has led to the emergence of a new field in the literature, climate finance. In turn, the use of Machine Learning (ML) as a tool to analyze climate finance is on the rise, due to the need to use big data to collect new climate-related information and model complex non-linear relationships. Considering the proliferation of articles in this field, and the potential for the use of ML, we propose a review of the academic literature to assess how ML is enabling climate finance to scale up. The main contribution of this paper is to provide a structure of application domains in a highly fragmented research field, aiming to spur further innovative work from ML experts. To pursue this objective, first we perform a systematic search of three scientific databases to assemble a corpus of relevant studies. Using topic modeling (Latent Dirichlet Allocation) we uncover representative thematic clusters. This allows us to statistically identify seven granular areas where ML is playing a significant role in climate finance literature: natural hazards, biodiversity, agricultural risk, carbon markets, energy economics, ESG factors & investing, and climate data. Second, we perform an analysis highlighting publication trends; and thirdly, we show a breakdown of ML methods applied by research area.
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Marshall, Katherine. Towards Enriching Understandings and Assessments of Freedom of Religion or Belief: Politics, Debates, Methodologies, and Practices. Institute of Development Studies, gennaio 2021. http://dx.doi.org/10.19088/creid.2021.001.
Testo completoAbstract (sommario):
Promoting the right to freedom of religion or belief (FoRB) is a foreign policy priority for several countries, their concerns accentuated by considerable evidence of rising levels of violations of this right worldwide. This puts a premium on solid evidence and on clear assessment criteria to serve as objective guides for policy. This paper reviews the complex landscape of approaches to assessing and measuring both the status of FoRB and the degree to which this human right is being violated or protected. It introduces and describes various transnational methodologies, both qualitative and quantitative, which focus, in differing ways, on violations. Several are widely cited and have express policy applications, while others have more indirect application to FoRB. The analysis highlights the diversity of approaches, which both reflect and contribute to a tendency to politicise FoRB issues. Challenges include differing understandings of the nature and relative significance of violations and their comparability. Country analysis is crucial because the specific context has vital importance for a granular appreciation for causes and impact of FoRB violations. This granularity, however, is poorly reflected in broader quantitative transnational and time series indices that highlight trends and comparative impact. The review highlights the limited degree to which FoRB issues, specifically violations and religiously related discrimination, are integrated in the policies and practice of development approaches (including social change and progress towards wellbeing) internationally and nationally. Effective approaches to addressing violations are few and far between, especially at the international level. The review notes strengths and weaknesses of specific approaches to assessment and reflects on possible improvements focused on development challenges and better integration among aspects of human rights.
10
Or, Dani, Shmulik Friedman e Jeanette Norton. Physical processes affecting microbial habitats and activity in unsaturated agricultural soils. United States Department of Agriculture, ottobre 2002. http://dx.doi.org/10.32747/2002.7587239.bard.
Testo completoAbstract (sommario):
experimental methods for quantifying effects of water content and other dynamic environmental factors on bacterial growth in partially-saturated soils. Towards this end we reviewed critically the relevant scientific literature and performed theoretical and experimental studies of bacterial growth and activity in modeled, idealized and real unsaturated soils. The natural wetting-drying cycles common to agricultural soils affect water content and liquid organization resulting in fragmentation of aquatic habitats and limit hydraulic connections. Consequently, substrate diffusion pathways to soil microbial communities become limiting and reduce nutrient fluxes, microbial growth, and mobility. Key elements that govern the extent and manifestation of such ubiquitous interactions include characteristics of diffusion pathways and pore space, the timing, duration, and extent of environmental perturbations, the nature of microbiological adjustments (short-term and longterm), and spatial distribution and properties of EPS clusters (microcolonies). Of these key elements we have chosen to focus on a manageable subset namely on modeling microbial growth and coexistence on simple rough surfaces, and experiments on bacterial growth in variably saturated sand samples and columns. Our extensive review paper providing a definitive “snap-shot” of present scientific understanding of microbial behavior in unsaturated soils revealed a lack of modeling tools that are essential for enhanced predictability of microbial processes in soils. We therefore embarked on two pronged approach of development of simple microbial growth models based on diffusion-reaction principles to incorporate key controls for microbial activity in soils such as diffusion coefficients and temporal variations in soil water content (and related substrate diffusion rates), and development of new methodologies in support of experiments on microbial growth in simple and observable porous media under controlled water status conditions. Experimental efforts led to a series of microbial growth experiments in granular media under variable saturation and ambient conditions, and introduction of atomic force microscopy (AFM) and confocal scanning laser microscopy (CSLM) to study cell size, morphology and multi-cell arrangement at a high resolution from growth experiments in various porous media. The modeling efforts elucidated important links between unsaturated conditions and microbial coexistence which is believed to support the unparallel diversity found in soils. We examined the role of spatial and temporal variation in hydration conditions (such as exist in agricultural soils) on local growth rates and on interactions between two competing microbial species. Interestingly, the complexity of soil spaces and aquatic niches are necessary for supporting a rich microbial diversity and the wide array of microbial functions in unsaturated soils. This project supported collaboration between soil physicists and soil microbiologist that is absolutely essential for making progress in both disciplines. It provided a few basic tools (models, parameterization) for guiding future experiments and for gathering key information necessary for prediction of biological processes in agricultural soils. The project sparked a series of ongoing studies (at DTU and EPFL and in the ARO) into effects of soil hydration dynamics on microbial survival strategy under short term and prolonged desiccation (important for general scientific and agricultural applications).