Mechanical strength of aneurysmatic and dissected human thoracic aortas at different shear loading modes

Rupture of aneurysms and acute dissection of the thoracic aorta are life-threatening events which affect tens of thousands of people per year. The underlying mechanisms remain unclear and the aortic wall is known to lose its structural integrity, which in turn affects its mechanical response to the loading conditions. Hence, research on such aortic diseases is an important area in biomechanics. The present study investigates the mechanical properties of aneurysmatic and dissected human thoracic aortas via triaxial shear and uniaxial tensile testing with a focus on the former. In particular, ultimate stress values from triaxial shear tests in different orientations regarding the aorta's orthotropic microstructure, and from uniaxial tensile tests in radial, circumferential and longitudinal directions were determined. In total, 16 human thoracic aortas were investigated from which it is evident that the aortic media has much stronger resistance to rupture under ‘out-of-plane’ than under ‘in-plane’ shear loadings. Under different shear loadings the aortic tissues revealed anisotropic failure properties with higher ultimate shear stresses and amounts of shear in the longitudinal than in the circumferential direction. Furthermore, the aortic media decreased its tensile strength as follows: circumferential direction > longitudinal direction > radial direction. Anisotropic and nonlinear tissue properties are apparent from the experimental data. The results clearly showed interspecimen differences influenced by the anamnesis of the donors such as aortic diseases or connective tissue disorders, e.g., dissected specimens exhibited on average a markedly lower mechanical strength than aneurysmatic specimens. The rupture data based on the combination of triaxial shear and uniaxial extension testing are unique and build a good basis for developing a 3D failure criterion of diseased human thoracic aortic media. This is a step forward to more realistic modeling of mechanically induced tissue failure i.e. rupture of aneurysms or progression of aortic dissections

Fluid-structure interaction simulation of prosthetic aortic valves : comparison between immersed boundary and arbitrary Lagrangian-Eulerian techniques for the mesh representation

In recent years the role of FSI (fluid-structure interaction) simulations in the analysis of the fluid-mechanics of heart valves is becoming more and more important, being able to capture the interaction between the blood and both the surrounding biological tissues and the valve itself. When setting up an FSI simulation, several choices have to be made to select the most suitable approach for the case of interest: in particular, to simulate flexible leaflet cardiac valves, the type of discretization of the fluid domain is crucial, which can be described with an ALE (Arbitrary Lagrangian-Eulerian) or an Eulerian formulation. The majority of the reported 3D heart valve FSI simulations are performed with the Eulerian formulation, allowing for large deformations of the domains without compromising the quality of the fluid grid. Nevertheless, it is known that the ALE-FSI approach guarantees more accurate results at the interface between the solid and the fluid. The goal of this paper is to describe the same aortic valve model in the two cases, comparing the performances of an ALE-based FSI solution and an Eulerian-based FSI approach. After a first simplified 2D case, the aortic geometry was considered in a full 3D set-up. The model was kept as similar as possible in the two settings, to better compare the simulations' outcomes. Although for the 2D case the differences were unsubstantial, in our experience the performance of a full 3D ALE-FSI simulation was significantly limited by the technical problems and requirements inherent to the ALE formulation, mainly related to the mesh motion and deformation of the fluid domain. As a secondary outcome of this work, it is important to point out that the choice of the solver also influenced the reliability of the final results

Liederhandschrift Langebek : Handschrift "Langebeks kvart" : die deutschen Lieder in Langebeks Quarthandschrift (ca.1560-1590)

"Langebeks kvart" gehört zum Hauptbestand dänischer Liedüberlieferung der Renaissance [...]. Das besondere an gerade dieser Handschrift ist, dass sie unter insgesamt 178 Aufzeichnungen 71 deutsche Texte enthält

Einleitung und Arbeitsbibliographie zum Liedverzeichnis

Otto Holzapfel, Liedverzeichnis [Hildesheim: Olms, 2006], online Update Januar 2022. Dateien: Lieder, Lexikon, ergänzende Dateien [Gesamtverzeichnis im Aufbau] - Dieses Verzeichnis wendet sich an Philologen und Literaturwissenschaftler, an Germanisten und an Musikwissenschaftler, aber auch an interessierte Laien, die Auskunft über ein Lied und über den Kontext zur Liedüberlieferung suchen

Lieddatei – Lieder L bis Z [Online Update März 2023]

Otto Holzapfel, Liedverzeichnis, Lieder L bis Z, online Update März 2023. [Gesamtverzeichnis im Aufbau]

Dil Çağrışımı ve Dil Kullanımı

Adjektivbildungen mit unterschiedlichen Suffixen sind im Deutschen häufig, aber der differenzierte Gebrauch entspricht gewollten Bedeutungsunterschieden. Diese Bildungen scheinen keiner durchgehenden Systematik entsprechen zu wollen, sondern gehorchen in ihrer möglichen Verwendung der Konvention, der herrschenden Übereinkunft über den Alltagssprachgebrauch. Diesen muss man jeweils am Einzelbeispiel erlernen. Das Eindringen in das Verständnis solcher Möglichkeiten verfeinert das Sprachgefühl in erheblichem Maß. Solches kann man auch in den Unterricht einbringen.Almancada farklı soneklerle sıfat çekimi sık yapılır; bilinçli kullanım istendik anlam farklılıklarını yaratır. Bu sıfat çekimleri belirli bir sistematiğe uymuyor görünmekte, aksine olası kullanım durumunda geleneğe, günlük dil kullanımı konusundaki uzlaşmaya uygun gerçekleşiyor. Her bir kullanımı ise ayrı ayrı öğrenmek gerekmektedir. Bu tür olanakların anlaşılmasına vakıf olmak, dil duygusunu önemli ölçüde geliştirmektedir. Bu husus derslerde ele alınabilir

Liederhandschriften DVA Freiburg : "Handschriftliche Liederbücher" : Verzeichnis von Liederhandschriften im DVA [ergänzter Stand: März 2009; Verweise angepasst Februar 2022]

Auswahl handschriftlicher Liederbücher, vorwiegend aus Franken und Bayern, im Bestand des Deutschen Volksliedarchivs (DVA), Freiburg i.Br., und in Kopien im Volksmusikarchiv des Bezirks Oberbayern (VMA), Bruckmühl

Liedverzeichnis [Online Update Januar bis März 2022] : Inhaltsverzeichnis

Inhaltsverzeichnis zum Liedverzeichnis : die ältere deutschsprachige, populäre Liedüberlieferung (in Zusammenarbeit mit dem Volksmusikarchiv des Bezirks Oberbayern, Bruckmühl) [Online Update Januar - März 2022