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1,384 results on '"Walther F"'

1. Defect-based characterization of the fatigue behavior of additively manufactured titanium aluminides

Author

Teschke, M., Moritz, J., Tenkamp, J., Marquardt, A., Leyens, C., and Walther, F.

Subjects
Condensed Matter - Materials Science, Physics - Applied Physics
Abstract

The additively manufactured titanium aluminide alloy TNM-B1 was characterized microstructurally and mechanically in the as-built and hot isostatically pressed (HIP) condition. Tensile and constant amplitude tests were performed at room temperature and 800 {\deg}C. Using fractographic SEM images, the fracture-inducing defect was identified. With the HIP, defect number and size could be reduced, increasing fatigue strength by 43% to 500 MPa. Using the model approaches of Murakami and Shiozawa, the fatigue life was correlated with the local stress intensity factor and could be described as function of the stress amplitude as well as the size and location of fracture-inducing defects., Comment: 24 pages, 10 figures, 2 tables

Published
2022

10. Modeling Coating Flow and Surfactant Dynamics inside the Alveolar Compartment

Author

Kang, D., Chugunova, M., Nadim, A., Waring, A. J., and Walther, F. J.

Subjects
Physics - Medical Physics, Condensed Matter - Soft Condensed Matter
Abstract

We derive a new model for the coating flow inside the alveolar compartment, taking into account pulmonary surfactant production and recycling by Type 2 cells as well as its degradation. As the thickness of alveolar coating is much smaller than the average radius of the alveoli, we employ the classical lubrication approximation to describe the thin liquid film dynamics in the presence of pulmonary surfactant, which is a surface tension reducing agent and thus prevents the lungs from collapse. In the lubrication limit, we derive a degenerate system of two coupled parabolic partial differential equations that describe the time evolution of the thickness of the coating film inside the alveoli together with that of the surfactant concentration at the interface. We present numerical simulations using parameter values consistent with experimental measurements.

Published
2018

19. Ge doping of GaN beyond the Mott transition

Author

Ajay, A., Schörmann, J., Jimenez-Rodriguez, M., Lim, C. B., Walther, F., Rohnke, M., Mouton, I., Amichi, L., Bougerol, C., Hertog, M. I. Den, Eickhoff, M., and Monroy, E.

Subjects
Condensed Matter - Materials Science
Abstract

We present a study of germanium as n-type dopant in wurtzite GaN films grown by plasma-assisted molecular beam epitaxy, reaching carrier concentrations of up to 6.7E20 cm-3 at 300K, well beyond the Mott density. The Ge concentration and free carrier density were found to scale linearly with the Ge flux in the studied range. All the GaN:Ge layers present smooth surface morphology with atomic terraces, without trace of pits or cracks, and the mosaicity of the samples has no noticeable dependence on the Ge concentration. The variation of the GaN:Ge band gap with the carrier concentration is consistent with theoretical calculations of the band gap renormalization due to electron-electron and electron-ion interaction, and Burstein-Moss effect.

Published
2016
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25. Characterization of the Fatigue Behavior of Mechanical and Thermal Aged Austenitic Power Plant Steel AISI 347

Author

Maci, F., Jamrozy, M., Acosta, R., Starke, P., Boller, C., Heckmann, K., Sievers, J., Schopf, T., Walther, F., Correia, José A.F.O., Series Editor, De Jesus, Abílio M.P., Series Editor, Ayatollahi, Majid Reza, Advisory Editor, Berto, Filippo, Advisory Editor, Fernández-Canteli, Alfonso, Advisory Editor, Hebdon, Matthew, Advisory Editor, Kotousov, Andrei, Advisory Editor, Lesiuk, Grzegorz, Advisory Editor, Murakami, Yukitaka, Advisory Editor, Carvalho, Hermes, Advisory Editor, Zhu, Shun-Peng, Advisory Editor, Fernandes, António Augusto, editor, and Calçada, Rui, editor

Published
2019
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26. Micromagnetic-Based Fatigue Life Prediction of Single-Lip Deep Drilled AISI 4140

Author

Baak, N., Nickel, J., Biermann, D., Walther, F., Correia, José A.F.O., Series Editor, De Jesus, Abílio M.P., Series Editor, Ayatollahi, Majid Reza, Advisory Editor, Berto, Filippo, Advisory Editor, Fernández-Canteli, Alfonso, Advisory Editor, Hebdon, Matthew, Advisory Editor, Kotousov, Andrei, Advisory Editor, Lesiuk, Grzegorz, Advisory Editor, Murakami, Yukitaka, Advisory Editor, Carvalho, Hermes, Advisory Editor, Zhu, Shun-Peng, Advisory Editor, Fernandes, António Augusto, editor, and Calçada, Rui, editor

Published
2019
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33. Deficiency or inhibition of lysophosphatidic acid receptor 1 protects against hyperoxia-induced lung injury in neonatal rats.

Author

Chen, X, Walther, F, van Boxtel, R, Laghmani, E, Sengers, R, Folkerts, G, DeRuiter, M, Cuppen, E, and Wagenaar, G

Subjects
bronchopulmonary dysplasia, fibrosis, lung inflammation, lysophosphatidic acid receptor, right ventricular hypertrophy, Animals, Animals, Newborn, Blotting, Western, Bronchopulmonary Dysplasia, Disease Models, Animal, Enzyme-Linked Immunosorbent Assay, Hyperoxia, Isoxazoles, Propionates, Rats, Rats, Mutant Strains, Rats, Wistar, Real-Time Polymerase Chain Reaction, Receptors, Lysophosphatidic Acid
Abstract

AIM: Blocking of lysophosphatidic acid (LPA) receptor (LPAR) 1 may be a novel therapeutic option for bronchopulmonary dysplasia (BPD) by preventing the LPAR1-mediated adverse effects of its ligand (LPA), consisting of lung inflammation, pulmonary arterial hypertension (PAH) and fibrosis. METHODS: In Wistar rats with experimental BPD, induced by continuous exposure to 100% oxygen for 10 days, we determined the beneficial effects of LPAR1 deficiency in neonatal rats with a missense mutation in cytoplasmic helix 8 of LPAR1 and of LPAR1 and -3 blocking with Ki16425. Parameters investigated included survival, lung and heart histopathology, fibrin and collagen deposition, vascular leakage and differential mRNA expression in the lungs of key genes involved in LPA signalling and BPD pathogenesis. RESULTS: LPAR1-mutant rats were protected against experimental BPD and mortality with reduced alveolar septal thickness, lung inflammation (reduced influx of macrophages and neutrophils, and CINC1 expression) and collagen III deposition. However, LPAR1-mutant rats were not protected against alveolar enlargement, increased medial wall thickness of small arterioles, fibrin deposition and vascular alveolar leakage. Treatment of experimental BPD with Ki16425 confirmed the data observed in LPAR1-mutant rats, but did not reduce the pulmonary influx of neutrophils, CINC1 expression and mortality in rats with experimental BPD. In addition, Ki16425 treatment protected against PAH and right ventricular hypertrophy. CONCLUSION: LPAR1 deficiency attenuates pulmonary injury by reducing pulmonary inflammation and fibrosis, thereby reducing mortality, but does not affect alveolar and vascular development and, unlike Ki16425 treatment, does not prevent PAH in neonatal rats with experimental BPD.

Published
2016

41. Towards reliable micromagnetic detection of white etching layers in deep drilled quenched and tempered steels

Author

Strodick, Simon, Steffens, D., Walther, F., Schmidt, R., Zabel, A., Biermann, D., and 5. Symposium Materialtechnik, 23. bis 24. Februar 2023

Subjects
article, ddc:600
Abstract

Ultrafine-grained white etching layers (WEL) can be formed in the machining of steels, titanium alloys and nickel-based superalloys due to high forces and temperatures in the contact area of the tool and the workpiece. In general, these layers are associated with very high hardness and brittleness as well as (tensile) residual stresses. These mechanical properties of WEL can have a severely negative impact on the lifetime and reliability of components. As a result, it is of crucial importance to reliably detect WEL, understand the underlying mechanisms and physical relationships in their formation and finally control their emergence in machining. Currently, WEL are usually detected using destructive metallographic analyses. In recent years, therefore, the applicability of alternative non-destructive methods for the reliable detection of WEL has been increasingly investigated. In this context, methods such as X-ray diffraction, acoustic emission (AE) and eddy current testing were used. The analysis of magnetic Barkhausen noise (MBN) was identified as a particularly suitable method for the detection of WEL in steels with a very high potential for application in production technology. In this study, MBN analysis is employed for the time-efficient and non-destructive detection of WEL in deep drilled components made of the quenched and tempered steel AISI 4140. It is shown that WEL form in drilling, especially at high cutting speeds and feeds. The use of coated guide pads and cutting edges promotes the formation of WEL. Hardness in the WEL exceeds the hardness of the bulk material up to three times. Specimens with thick WEL can be separated from specimens free of WEL by significantly lower maximum magnetic Barkhausen noise amplitudes.

Published
2023
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42. Monitoring of the fatigue state of single-lip deep-drilled specimens made of the quenched and tempered steel AISI 4140 using micromagnetic methods

Author

Baak, Nikolas, Walther, F., Nickel, J., Biermann, D., and 5. Symposium Materialtechnik, 23. bis 24. Februar 2023

Subjects
article, ddc:600
Abstract

Fatigue is one of the main causes for the failure of technical components. Therefore, the monitoring of fatigue-related material degradation is a target-oriented way to extend the lifetime of safety-relevant components. In terms of sustainability and resource conservation, the implementation of reliable fatigue monitoring is of crucial importance. Fatigue damage is manifested by a variety of microstructural and micromechanical property changes such as grain refinement, relaxation of residual stresses, increase of dislocation density and hardness change. An application of micromagnetic techniques is very promising, since it is known that Barkhausen noise analysis and eddy current testing are sensitive to these parameters. This work deals with the separation of the micromagnetic parameters with respect to fatigue-induced changes. This separation is necessary to identify, quantify and evaluate the relevant fatigue damage mechanisms and thereby assess the remaining lifetime of the monitored components. In this work, multiple amplitude fatigue tests were performed on specimens drilled under different conditions and as a consequence partly feature a white etching layer. Under these aspects the capability of Barkhausen noise analysis and eddy current testing was compared and assessed.

Published
2023

46. An Ultra-deep Multiband Very Large Array (VLA) Survey of the Faint Radio Sky (COSMOS-XS): New Constraints on the Cosmic Star Formation History

Author

van der Vlugt, D., Hodge, J. A., Jin, S., Algera, H. S.B., Leslie, S. K., Riechers, D. A., Röttgering, H., Smolčić, V., Walther, F., van der Vlugt, D., Hodge, J. A., Jin, S., Algera, H. S.B., Leslie, S. K., Riechers, D. A., Röttgering, H., Smolčić, V., and Walther, F.

Abstract

Attempts to trace star formation with rest-frame UV/optical observations at redshifts z > 2 are affected by the presence of potentially substantial, yet uncertain, dust attenuation. Recent studies have demonstrated the existence of a population of galaxies that are virtually invisible in the observed optical/near-infrared (NIR) due to dust obscuration, but which could contribute substantially to the star formation history at 2 < z < 6. Here, we make use of ultradeep 3 GHz Karl G. Jansky Very Large Array observations from the COSMOS-XS survey to investigate the contribution 20of radio-selected "optically dark" galaxies (undetected to a depth of KS ∼ 25.9 mag) to the cosmic star formation rate density (SFRD). We identify 19 such "optically dark" sources and utilize recent deblended far-infrared photometry to determine photometric redshifts based on IR and radio information for 11 of them. Through stacking, we infer that the remaining eight sources reside predominantly at high redshift (z > 4). Therefore, we conservatively assume these sources lie between z = 2 and z = 5. We derive the radio luminosity function (LF) for the sample with and without "optically dark" sources by fixing the faint and bright end shape of the radio LF to the local values and allowing for luminosity evolution.

Published
2023

47. An Ultradeep Multiband Very Large Array Survey of the Faint Radio Sky (COSMOS-XS): New Constraints on the Optically Dark Population

Author

van der Vlugt, D., Hodge, J. A., Jin, S., Algera, H. S.B., Leslie, S. K., Riechers, D. A., Röttgering, H., Smolčić, V., Walther, F., van der Vlugt, D., Hodge, J. A., Jin, S., Algera, H. S.B., Leslie, S. K., Riechers, D. A., Röttgering, H., Smolčić, V., and Walther, F.

Abstract

Attempts to trace star formation with rest-frame UV/optical observations at redshifts z > 2 are affected by the presence of potentially substantial, yet uncertain, dust attenuation. Recent studies have demonstrated the existence of a population of galaxies that are virtually invisible in the observed optical/near-infrared (NIR) due to dust obscuration, but which could contribute substantially to the star formation history at 2 < z < 6. Here, we make use of ultradeep 3 GHz Karl G. Jansky Very Large Array observations from the COSMOS-XS survey to investigate the contribution 20of radio-selected "optically dark" galaxies (undetected to a depth of KS ∼ 25.9 mag) to the cosmic star formation rate density (SFRD). We identify 19 such "optically dark" sources and utilize recent deblended far-infrared photometry to determine photometric redshifts based on IR and radio information for 11 of them. Through stacking, we infer that the remaining eight sources reside predominantly at high redshift (z > 4). Therefore, we conservatively assume these sources lie between z = 2 and z = 5. We derive the radio luminosity function (LF) for the sample with and without "optically dark" sources by fixing the faint and bright end shape of the radio LF to the local values and allowing for luminosity evolution.

Published
2023

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