221 research outputs found

    Streamline Simulation to Improve Polymer Enhanced Oil Recovery for a Mature Oil Field in Austria

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    Influence of process gas during powder bed fusion with laser beam of Zr-based bulk metallic glasses

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    Zr-based bulk metallic glasses offer a unique combination of hardness, high strength, and high elastic limits. Yet, manufacturable size and complexity are limited due to the required cooling rates. Short laser-material interaction times together with layer-wise and selective energy input allows the laser powder bed fusion process to largely overcome those restrictions. Still, the complex process-material interactions inhere numerous uncertainties. In the present work, additively manufactured Zr-based bulk metallic glasses produced under three different process gases are investigated by calorimetry, x-ray diffraction, and bending tests. A strong dependence between the thermophysical properties, flexural strength, and the applied atmosphere is found

    Material Extrusion of Structural Polymer–Aluminum Joints—Examining Shear Strength, Wetting, Polymer Melt Rheology and Aging

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    Generating polymer–metal structures by means of additive manufacturing offers huge potential for customized, sustainable and lightweight solutions. However, challenges exist, primarily with regard to reliability and reproducibility of the additively generated joints. In this study, the polymers ABS, PETG and PLA, which are common in material extrusion, were joined to grit-blasted aluminum substrates. Temperature dependence of polymer melt rheology, wetting and tensile single lap-shear strength were examined in order to obtain appropriate thermal processing conditions. Joints with high adhesive strength in the fresh state were aged for up to 100 days in two different moderate environments. For the given conditions, PETG was most suitable for generating structural joints. Contrary to PETG, ABS–aluminum joints in the fresh state as well as PLA–aluminum joints in the aged state did not meet the demands of a structural joint. For the considered polymers and processing conditions, this study implies that the suitability of a polymer and a thermal processing condition to form a polymer–aluminum joint by material extrusion can be evaluated based on the polymer’s rheological properties. Moreover, wetting experiments improved estimation of the resulting tensile single-lap-shear strength

    SARS-CoV-2 in Pediatric Inpatient Care: Management, Clinical Presentation and Utilization of Healthcare Capacity

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    This study scrutinizes management and clinical presentation of severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) in pediatric inpatient care and evaluates the utilization of pediatric healthcare capacity during the pandemic. Within this retrospective cohort study, we systematically reviewed data of all 16,785 pediatric patients (<18 years admitted to our clinical center between January 2018 and June 2021). Data on SARS-CoV-2 test numbers, hospital admissions and clinical characteristics of infected patients were collected. Since January 2020, a total of 2513 SARS-CoV-2 tests were performed. In total, 36 patients had a positive test result. In total, 25 out of 36 SARS-CoV-2 positive children showed at least mild clinical symptoms while 11 were asymptomatic. Most common clinical symptoms were fever (60%), cough (60%) and rhinitis (20%). In parallel with the rising slope of SARS-CoV-2 in spring and fall 2020, we observed a slight decrease in the number of patients admitted to the pediatric department while the median duration of hospital treatment and intensive care occupancy remained unchanged. This study underlines that SARS-CoV-2 infected children most frequently exhibit an asymptomatic or mild clinical course. Noteworthy, the number of hospital admissions went down during the pandemic. The health and economic consequences need to be discussed within health care society and politics

    Influence of Processing Route on the Surface Reactivity of Cu47Ti33Zr11Ni6Sn2Si1 Metallic Glass

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    Recently, laser additive manufacturing (AM) techniques have emerged as a promising alternative for the synthesis of bulk metallic glasses (BMGs) with massively increased freedom in part size and geometry, thus extending their economic applicability of this material class. Nevertheless, porosity, compositional inhomogeneity, and crystallization display themselves to be the emerging challenges for this processing route. The impact of these “defects” on the surface reactivity and susceptibility to corrosion was seldom investigated but is critical for the further development of 3D-printed BMGs. This work compares the surface reactivity of cast and additively manufactured (via laser powder bed fusion—LPBF) Cu47Ti33Zr11Ni6Sn2Si1 metallic glass after 21 days of immersion in a corrosive HCl solution. The cast material presents lower oxygen content, homogeneous chemical distribution of the main elements, and the surface remains unaffected after the corrosion experimentation based on vertical scanning interferometry (VSI) investigation. On the contrary, the LPBF material presents a considerably higher reactivity seen through crack propagations on the surface. It exhibits higher oxygen content, heterogeneous chemical distribution, and presence of defects (porosity and cracks) generated during the manufacturing process

    Differences in structure and dynamics of ternary Pd–Ni-based bulk metallic glasses containing sulfur or phosphorous

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    The composition Pd31_{31}Ni42_{42}S27_{27} has been shown to be the best glass former in the family of recently discovered glass forming PdNiS alloys. In this study, this sample system was systematically investigated using fluctuation- and correlation electron microscopy of which the results are compared to a Pd40_{40}Ni40_{40}P20_{20} bulk metallic glass that serves as a model system for metallic glasses. Strong differences in the local atomic correlations beyond the short-range order were observed, which are assumed to be a reason for their discrepancy in thermal stability. The relaxation dynamics at room temperature revealed faster dynamics in the sulfur-containing Pd31_{31}Ni42_{42}S27_{27} glass

    Development and optimization of novel sulfur-containing Ti-based bulk metallic glasses and the correlation between primarily crystallizing phases, thermal stability and mechanical properties

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    The effect of sulfur on the glass forming ability, thermal stability and mechanical properties of the eutectic alloy Ti33.4Zr33.3Cu33.3 was investigated by conventional X-ray diffraction, differential scanning calorimetry and 3-point flexural experiments. A novel region of bulk glass formation with a critical casting diameter of up to 4 mm was found in the quaternary Ti-Zr-Cu-S system, however, brittle fracture behavior was predominant. Various alloying strategies were employed to improve mechanical properties and a compositional transition from brittle to ductile fracture has been identified (e.g. for Ti36Zr33.5Cu24.5S6). A change of the primary precipitating phases from a C14 Laves to an intermetallic (Ti,Zr)2Cu phase can be observed, as well as a stabilization of the supercooled liquid. The origin of the thermally unstable behavior in Ti-based bulk metallic glasses is traced back to the easy formation of the icosahedral phase upon heating, which is structurally close to the supposedly predominant icosahedral short-range order in the amorphous state. The systematic study carried out in this work indicates a strong correlation between primary crystallizing phase and thermal stability, both pointing to the frozen short-range order in the amorphous state which is predetermining the mechanical properties. The transition from the Laves to the intermetallic (Ti,Zr)2Cu phase as well as the enlarged supercooled liquid region appear to be directly related to a destabilization of the icosahedral short-range order and ultimately to the improved mechanical properties

    Size-dependent vitrification in metallic glasses

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    Reducing the sample size can profoundly impact properties of bulk metallic glasses. Here, we systematically reduce the length scale of Au and Pt-based metallic glasses and study their vitrification behavior and atomic mobility. For this purpose, we exploit fast scanning calorimetry (FSC) allowing to study glassy dynamics in an exceptionally wide range of cooling rates and frequencies. We show that the main α relaxation process remains size independent and bulk-like. In contrast, we observe pronounced size dependent vitrification kinetics in micrometer-sized glasses, which is more evident for the smallest samples and at low cooling rates, resulting in more than 40 K decrease in fictive temperature, Tf, with respect to the bulk. We discuss the deep implications on how this outcome can be used to convey glasses to low energy states

    Verbrennungsprodukte und Gesundheit: Ruß und Größenverteilung ultrafeiner und feiner Partikel in der Außenluft in Leipzig und Dresden und Gesundheit: Abschlussbericht

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    Die Publikation dokumentiert die Ergebnisse der epidemiologischen Studie zu gesundheitlichen Auswirkungen von ultrafeinen und feinen Partikeln und Ruß. Wie sich ultrafeine Partikel auf die Gesundheit auswirken, ist bisher noch nicht ausreichend untersucht. Mit der Auswertung der langen Messreihen von Dresden, Leipzig und Augsburg leistet die Studie deshalb einen Beitrag zum besseren Verständnis der Folgen von Luftschadstoffen auf die menschliche Gesundheit. Die Analysen zeigten erhöhte Risiken sowohl für respiratorische Mortalität als auch für die Hospitalisierung zu unterschiedlichen Zeitpunkten nach der Exposition mit ultrafeinen Partikeln. Dabei stieg das Risiko beispielsweise in der kalten Jahreshälfte stärker an. Die Veröffentlichung richtet sich an Vertreter von Fachbehörden und Forschungseinrichtungen, aber auch an die interessierte Öffentlichkeit. Redaktionsschluss: 05.01.202
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