Experimental analysis of spatter generation and melt-pool behavior during the powder bed laser beam melting process

The experimental analysis of spatter formation was carried out on an instrumented SLM set-up allowing the quantification of spatter ejections and possible correlation with melt-pool behavior. Considering nearly similar SLM conditions than those carried out on SLM machines, an increase of large spatters (>80 μm) with volume energy density (VED) was clearly demonstrated on a 316L stainless steel, which was attributed to the recoil pressure applied on the melt-pool by the metal vaporization and the resulting high velocity vapor plume. In a second step, much lower spattering was shown on Al-12Si powder beds than on 316L ones. Fast camera analysis of powder beds indicated that droplet formation was mostly initiated in the powder-bed near the melt-pool interface. On Al-12 Si alloys, such droplets were directly incorporated in the MP without being ejected upwards as spatters like on 316L. Last, it was shown that a strong reduction of spattering was possible even on 316L, with the use of low VED combined with larger spots (≈0.5 mm), allowing to melt sufficiently deep layers in conduction regime and ensure adequate dilution between layers

Analysis of laser–melt pool–powder bed interaction during the selective laser melting of a stainless steel

The laser powder bed fusion (LPBF) or powder-bed additive layer manufacturing process is now recognized as a high-potential manufacturing process for complex metallic parts. However, many technical issues are still to overcome for making LPBF a fully viable manufacturing process. This is the case of surface finish and the systematic occurrence of porosities, which require postmachining steps. Up till now, the porosity origin remains unclear but is expected to be related to the stability of the process. As a LPBF part is made by the accumulation of hundreds of meters of small weld beads, it also appears to be important to understand all the phenomena that occur during the laser-powder-melt pool (MP) interaction for each single track. For this reason, in the first part of our study, using an instrumented LPBF setup and a fast camera analysis (>10 000 image/s), single tracks were fabricated and analyzed in real time and postmortem. Spatters ejections and powder denudation phenomena were observed together with variations of melt pool dimensions and melt-pool instabilities. In turn, the physical origin of this powder denudation and the dynamics of the MP were investigated and discussed

Portrait of Ependymoma Recurrence in Children: Biomarkers of Tumor Progression Identified by Dual-Color Microarray-Based Gene Expression Analysis

BACKGROUND: Children with ependymoma may experience a relapse in up to 50% of cases depending on the extent of resection. Key biological events associated with recurrence are unknown. METHODOLOGY/PRINCIPAL FINDINGS: To discover the biology behind the recurrence of ependymomas, we performed CGHarray and a dual-color gene expression microarray analysis of 17 tumors at diagnosis co-hybridized with the corresponding 27 first or subsequent relapses from the same patient. As treatment and location had only limited influence on specific gene expression changes at relapse, we established a common signature for relapse. Eighty-seven genes showed an absolute fold change ≥2 in at least 50% of relapses and were defined as the gene expression signature of ependymoma recurrence. The most frequently upregulated genes are involved in the kinetochore (ASPM, KIF11) or in neural development (CD133, Wnt and Notch pathways). Metallothionein (MT) genes were downregulated in up to 80% of the recurrences. Quantitative PCR for ASPM, KIF11 and MT3 plus immunohistochemistry for ASPM and MT3 confirmed the microarray results. Immunohistochemistry on an independent series of 24 tumor pairs at diagnosis and at relapse confirmed the decrease of MT3 expression at recurrence in 17/24 tumor pairs (p = 0.002). Conversely, ASPM expression was more frequently positive at relapse (87.5% vs 37.5%, p = 0.03). Loss or deletion of the MT genes cluster was never observed at relapse. Promoter sequencing after bisulfite treatment of DNA from primary tumors and recurrences as well as treatment of short-term ependymoma cells cultures with a demethylating agent showed that methylation was not involved in MT3 downregulation. However, in vitro treatment with a histone deacetylase inhibitor or zinc restored MT3 expression. CONCLUSIONS/SIGNIFICANCE: The most frequent molecular events associated with ependymoma recurrence were over-expression of kinetochore proteins and down-regulation of metallothioneins. Metallothionein-3 expression is epigenetically controlled and can be restored in vitro by histone deacetylase inhibitors

Analysis and possible estimation of keyhole depths evolution, using laser operating parameters and material properties

The authors propose an analysis of the effect of various operating parameters on the keyhole depth during laser welding. The authors have developed a model that uses the analysis of the thermal field obtained in 2D geometry, which is mainly defined by the characteristic Peclet number. This allows us to show that the dependence of the aspect ratio R of the keyhole with the operating parameters of the process is a function of two parameters: a normalized aspect ratio R0, controlled by the incident laser power and the spot diameter, and a characteristic speed V0 related to the process of heat diffusion. The resulting general law R = f (R0, V/V0) appears to be very well verified by different experimental data and allows to define mean thermophysical parameters of the used materials. These data can then be used for keyhole depths prediction for any subsequent operating parameters of the same material. This model also allows us to define precisely a criterion for a keyhole threshold generation. The authors will apply the derived procedure to successfully analyze experiments on materials with very different thermophysical properties (such as steel alloys and copper), with various focal spots, incident laser powers, and welding speeds

Transformations biologiques impliquées dans la dégradation des revêtements cimentaires en réseau d'assainissement : application à la définition d'un test de résistance à la biodétérioration

The primary function of sewage networks, with a view to protecting public health, is to collect wastewater and convey it to wastewater treatment plant. Under specific operating conditions leading to the production of hydrogen sulfide (H2S), major deterioration of concrete infrastructures is observed in the gas phase of these same networks. Studies have shown that an H2S environment leads to the selection, in contact with cement walls, of bacteria enable oxidizing reduced sulfur compounds (sulfo-oxidizing bacteria), biological oxidation leading to the production of acid and sulfate. In the context of the "NF EN 598" standard for ductile cast iron pipes and the "NF EN 14647" standard requiring the validation of coatings that can be used in such conditions using purely chemical tests that are not very representative of reality, LISBP, in partnership with Saint-Gobain PAM, carried out this Phd work with the industrial objective of developing a biodeterioration test for cementitious materials.To meet this objective, this research project was based on a literature review of the phenomena involved in the biodeterioration of cementitious materials in wastewater networks, with a view to proposing a model experimental set-up for the coupled study, on the scale of an industrial pipe section, of the biological and chemical transformations determining the fate of the cementitious materials used. This study was based on experimental laboratory work and the development of numerical models, aimed at selecting and understanding biogenic acid-producing sulfo-oxidizing bacteria. Finally, 2 types of cementitious materials were exposed and studied afer exposure by analysis of the chemical, mineralogical and microstructural evolutions of the tested materials. In this way, a model system was proposed, defining an experimental set-up (associated analytical techniques) and methods for exploiting the measurements. With this approach, a new test protocol is proposed, helping to assess the resistance of cementitious coatings used in sewer networks to biogenic acid attack. This three-month test protocol will ultimately provide a decision-making aid for the management of existing wastewater networks and the design of future networks.La fonction première des réseaux d’assainissement, en vue de la protection sanitaire des populations, est la collecte des eaux usées et leur acheminement vers les installations de traitement. Dans des conditions d’exploitations particulières conduisant à la production de sulfure d’hydrogène (H2S), des détériorations majeures des infrastructures en béton sont observées dans les phases aériennes de ces mêmes réseaux. En effet, des études ont montré qu’un environement H2S entrainait la sélection au contact des parois cimentaires de bactéries capables d’oxyder les composés soufrés réduits (bactéries sulfo-oxydantes), oxydation biologique conduisant à la production d’acide et de sulfate. Dans un contexte normatif « NF EN 598 » concernant les canalisations en fonte ductile et « NF EN 14647 » imposant la validation des revêtements utilisables dans de telles conditions par des tests uniquement chimiques peu représentatifs de la réalité, le LISBP en partenariat avec l’entreprise Saint-Gobain PAM, ont mené ce travail de thèse avec pour objectif industriel le dévelopment d’un test de biodétérioration des revêtements cimentaires. Pour répondre à cet objectif ce projet de recherche s’est articulé autour d’une analyse bibliographique des phénomènes participant à la biodétérioration des matériaux cimentaires en réseau d’assainissement et ce afin de proposer un dispositif expérimental modèle permettant, à l’échelle d’une section de canalisation industrielle, l’étude couplée des transformations biologiques et chimiques déterminant le devenir des revêtements cimentaires utilisés. Cette étude s’est alors appuyée sur un travail expérimental en laboratoire et le développement de models numériques, visant la sélection et la compréhension de bactéries sulfo-oxydantes productrices de l’acide biogéniques. Finalement 2 types de matériaux cimentaires ont été exposés et étudiés par une analyse près exposition des évolutions chimiques, minéralogiques et microstructurelles des revêtements testés. Ainsi un système modèle, définissant un dispositif expérimental (techniques analytiques associées) et les méthodes d’exploitation des mesures, a été proposé. Par cette approche, un nouveau protocole d’essai est proposé, participant à l’évaluation de la résistance des revêtements cimentaires utilisés en réseau d’assainissement face à des attaques d’acide biogénique. Ce protocole d’essais d’une durée de trois mois assurera à terme une aide à la décision dans la gestion des réseaux d’assainissement existants et la conception des réseaux futurs

Transformations biologiques impliquées dans la dégradation des revêtements cimentaires en réseau d'assainissement : application à la définition d'un test de résistance à la biodétérioration

The primary function of sewage networks, with a view to protecting public health, is to collect wastewater and convey it to wastewater treatment plant. Under specific operating conditions leading to the production of hydrogen sulfide (H2S), major deterioration of concrete infrastructures is observed in the gas phase of these same networks. Studies have shown that an H2S environment leads to the selection, in contact with cement walls, of bacteria enable oxidizing reduced sulfur compounds (sulfo-oxidizing bacteria), biological oxidation leading to the production of acid and sulfate. In the context of the "NF EN 598" standard for ductile cast iron pipes and the "NF EN 14647" standard requiring the validation of coatings that can be used in such conditions using purely chemical tests that are not very representative of reality, LISBP, in partnership with Saint-Gobain PAM, carried out this Phd work with the industrial objective of developing a biodeterioration test for cementitious materials.To meet this objective, this research project was based on a literature review of the phenomena involved in the biodeterioration of cementitious materials in wastewater networks, with a view to proposing a model experimental set-up for the coupled study, on the scale of an industrial pipe section, of the biological and chemical transformations determining the fate of the cementitious materials used. This study was based on experimental laboratory work and the development of numerical models, aimed at selecting and understanding biogenic acid-producing sulfo-oxidizing bacteria. Finally, 2 types of cementitious materials were exposed and studied afer exposure by analysis of the chemical, mineralogical and microstructural evolutions of the tested materials. In this way, a model system was proposed, defining an experimental set-up (associated analytical techniques) and methods for exploiting the measurements. With this approach, a new test protocol is proposed, helping to assess the resistance of cementitious coatings used in sewer networks to biogenic acid attack. This three-month test protocol will ultimately provide a decision-making aid for the management of existing wastewater networks and the design of future networks.La fonction première des réseaux d’assainissement, en vue de la protection sanitaire des populations, est la collecte des eaux usées et leur acheminement vers les installations de traitement. Dans des conditions d’exploitations particulières conduisant à la production de sulfure d’hydrogène (H2S), des détériorations majeures des infrastructures en béton sont observées dans les phases aériennes de ces mêmes réseaux. En effet, des études ont montré qu’un environement H2S entrainait la sélection au contact des parois cimentaires de bactéries capables d’oxyder les composés soufrés réduits (bactéries sulfo-oxydantes), oxydation biologique conduisant à la production d’acide et de sulfate. Dans un contexte normatif « NF EN 598 » concernant les canalisations en fonte ductile et « NF EN 14647 » imposant la validation des revêtements utilisables dans de telles conditions par des tests uniquement chimiques peu représentatifs de la réalité, le LISBP en partenariat avec l’entreprise Saint-Gobain PAM, ont mené ce travail de thèse avec pour objectif industriel le dévelopment d’un test de biodétérioration des revêtements cimentaires. Pour répondre à cet objectif ce projet de recherche s’est articulé autour d’une analyse bibliographique des phénomènes participant à la biodétérioration des matériaux cimentaires en réseau d’assainissement et ce afin de proposer un dispositif expérimental modèle permettant, à l’échelle d’une section de canalisation industrielle, l’étude couplée des transformations biologiques et chimiques déterminant le devenir des revêtements cimentaires utilisés. Cette étude s’est alors appuyée sur un travail expérimental en laboratoire et le développement de models numériques, visant la sélection et la compréhension de bactéries sulfo-oxydantes productrices de l’acide biogéniques. Finalement 2 types de matériaux cimentaires ont été exposés et étudiés par une analyse près exposition des évolutions chimiques, minéralogiques et microstructurelles des revêtements testés. Ainsi un système modèle, définissant un dispositif expérimental (techniques analytiques associées) et les méthodes d’exploitation des mesures, a été proposé. Par cette approche, un nouveau protocole d’essai est proposé, participant à l’évaluation de la résistance des revêtements cimentaires utilisés en réseau d’assainissement face à des attaques d’acide biogénique. Ce protocole d’essais d’une durée de trois mois assurera à terme une aide à la décision dans la gestion des réseaux d’assainissement existants et la conception des réseaux futurs

Biological transformations involved in the deterioration of the cementitious linings in sewer-networks : Application for the definition of a biodeterioration resistance test

La fonction première des réseaux d’assainissement, en vue de la protection sanitaire des populations, est la collecte des eaux usées et leur acheminement vers les installations de traitement. Dans des conditions d’exploitations particulières conduisant à la production de sulfure d’hydrogène (H2S), des détériorations majeures des infrastructures en béton sont observées dans les phases aériennes de ces mêmes réseaux. En effet, des études ont montré qu’un environement H2S entrainait la sélection au contact des parois cimentaires de bactéries capables d’oxyder les composés soufrés réduits (bactéries sulfo-oxydantes), oxydation biologique conduisant à la production d’acide et de sulfate. Dans un contexte normatif « NF EN 598 » concernant les canalisations en fonte ductile et « NF EN 14647 » imposant la validation des revêtements utilisables dans de telles conditions par des tests uniquement chimiques peu représentatifs de la réalité, le LISBP en partenariat avec l’entreprise Saint-Gobain PAM, ont mené ce travail de thèse avec pour objectif industriel le dévelopment d’un test de biodétérioration des revêtements cimentaires. Pour répondre à cet objectif ce projet de recherche s’est articulé autour d’une analyse bibliographique des phénomènes participant à la biodétérioration des matériaux cimentaires en réseau d’assainissement et ce afin de proposer un dispositif expérimental modèle permettant, à l’échelle d’une section de canalisation industrielle, l’étude couplée des transformations biologiques et chimiques déterminant le devenir des revêtements cimentaires utilisés. Cette étude s’est alors appuyée sur un travail expérimental en laboratoire et le développement de models numériques, visant la sélection et la compréhension de bactéries sulfo-oxydantes productrices de l’acide biogéniques. Finalement 2 types de matériaux cimentaires ont été exposés et étudiés par une analyse près exposition des évolutions chimiques, minéralogiques et microstructurelles des revêtements testés. Ainsi un système modèle, définissant un dispositif expérimental (techniques analytiques associées) et les méthodes d’exploitation des mesures, a été proposé. Par cette approche, un nouveau protocole d’essai est proposé, participant à l’évaluation de la résistance des revêtements cimentaires utilisés en réseau d’assainissement face à des attaques d’acide biogénique. Ce protocole d’essais d’une durée de trois mois assurera à terme une aide à la décision dans la gestion des réseaux d’assainissement existants et la conception des réseaux futurs.The primary function of sewage networks, with a view to protecting public health, is to collect wastewater and convey it to wastewater treatment plant. Under specific operating conditions leading to the production of hydrogen sulfide (H2S), major deterioration of concrete infrastructures is observed in the gas phase of these same networks. Studies have shown that an H2S environment leads to the selection, in contact with cement walls, of bacteria enable oxidizing reduced sulfur compounds (sulfo-oxidizing bacteria), biological oxidation leading to the production of acid and sulfate. In the context of the "NF EN 598" standard for ductile cast iron pipes and the "NF EN 14647" standard requiring the validation of coatings that can be used in such conditions using purely chemical tests that are not very representative of reality, LISBP, in partnership with Saint-Gobain PAM, carried out this Phd work with the industrial objective of developing a biodeterioration test for cementitious materials.To meet this objective, this research project was based on a literature review of the phenomena involved in the biodeterioration of cementitious materials in wastewater networks, with a view to proposing a model experimental set-up for the coupled study, on the scale of an industrial pipe section, of the biological and chemical transformations determining the fate of the cementitious materials used. This study was based on experimental laboratory work and the development of numerical models, aimed at selecting and understanding biogenic acid-producing sulfo-oxidizing bacteria. Finally, 2 types of cementitious materials were exposed and studied afer exposure by analysis of the chemical, mineralogical and microstructural evolutions of the tested materials. In this way, a model system was proposed, defining an experimental set-up (associated analytical techniques) and methods for exploiting the measurements. With this approach, a new test protocol is proposed, helping to assess the resistance of cementitious coatings used in sewer networks to biogenic acid attack. This three-month test protocol will ultimately provide a decision-making aid for the management of existing wastewater networks and the design of future networks

Mouse Models in Meningioma Research: A Systematic Review

International audienceMeningiomas are the most frequent primitive central nervous system tumors found in adults. Mouse models of cancer have been instrumental in understanding disease mechanisms and establishing preclinical drug testing. Various mouse models of meningioma have been developed over time, evolving in light of new discoveries in our comprehension of meningioma biology and with improvements in genetic engineering techniques. We reviewed all mouse models of meningioma described in the literature, including xenograft models (orthotopic or heterotopic) with human cell lines or patient derived tumors, and genetically engineered mouse models (GEMMs). Xenograft models provided useful tools for preclinical testing of a huge range of innovative drugs and therapeutic options, which are summarized in this review. GEMMs offer the possibility of mimicking human meningiomas at the histological, anatomical, and genetic level and have been invaluable in enabling tumorigenesis mechanisms, including initiation and progression, to be dissected. Currently, researchers have a range of different mouse models that can be used depending on the scientific question to be answered

Blast-furnace slag cement and metakaolin based geopolymer as construction materials for liquid anaerobic digestion structures: Interactions and biodeterioration mechanisms

International audienceIn order to promote the development of the biogas industry, solutions are needed to improve concrete structures durability in this environment. This multiphysics study aims to analyse the multiphases interactions between the liquid phase of an anaerobic digestion system and cementitious matrices, focusing on (i) the impacts of the binder nature on the anaerobic digestion process at local scale, and (ii) the deterioration mechanisms of the materials. Cementitious pastes made of slag cement (CEM III), innovative metakaolin-based alkali-activated material (MKAA), with compositions presumed to resist chemically aggressive media, and a reference binder, ordinary Portland cement (CEM I), were tested by immersion in inoculated cattle manure in bioreactors for a long period of five digestion cycles. For the first time it was shown that the digestion process was disturbed in the short term by the presence of the materials that increased the pH of the liquid phase and slowed the acids consumption, with much more impact of the MKAA. However, the final total production of biogas was similar in all bioreactors. Material analyses showed that, in this moderately aggressive medium, the biodeterioration of the CEM I and CEM III pastes mainly led to cement matrix leaching (decalcification) and carbonation. MKAA showed a good behaviour with very low degraded depths. In addition, the material was found to have interesting ammonium adsorption properties in the chemical conditions (notably the pH range) of anaerobic digestion