Effect of stacking fault energy on the restoration mechanisms and mechanical properties of friction stir welded copper alloys

Pure copper and Cu-Zn plates were friction stir welded under the same condition to evaluate the effect of stacking fault energy on the microstructural evolution and mechanical properties of the joints. For this aim, microstructure and texture of the joints were systematically characterized by electron backscattered diffraction and transmission electron microscopy. Moreover, to study the mechanical properties of the different microstructural zones of the joints, nanoindentation tests were employed. The results showed that in pure copper, continuous dynamic recrystallization was the only restoration mechanism for the formation of new grains. By adding zinc into copper, namely decreasing slacking fault energy, both continuous and discontinuous dynamic recryslallizalion mechanisms occurred. To this end, the enct of sucking fault energy on the restoration mechanisms has been summarized by schematic models. Moreover, the effect of the resloration mechanisms on the yield strength and strain hardening behavior of the joints has been scrutinized. (C) 2018 The Authors. Published by Elsevier Ltd

In situ characterization of the functional degradation of a [001] orientated Fe–Mn–Al–Ni single crystal under compression using acoustic emission measurements

Acoustic emission (AE) measurements were conducted in situ during cyclic compressive loading on an [ 00 1 over line ] orientated single crystal of Fe-Mn-Al-Ni shape memory alloy to study functional degradation of its superelastic response. The acoustic investigations were corroborated by optical microscopy, employing video imaging, and transmission electron microscopy. The analysis of acoustic emissions recorded during repeated loading and unloading sessions revealed two categories of AE signals that are differed by their characteristics in time and frequency domains. These two distinct types of AE signals were related to two underlying mechanisms: (i) the nucleation and reverse transformation of stress-induced (twinned) martensite, and (ii) the lateral growth and shrinkage of one dominant martensite variant and related dislocation activities, respectively. In addition, an asymmetry in the AE activity during forward and reverse transformation during mechanical loading and unloading was detected. In particular, an unexpected high AE activity was observed during the superelastic unloading of martensitic microstructure from the point of maximum load/strain. This effect was attributed to the reverse transformation of small, tiny areas of martensite as well as to unpinning and annihilation effects related to dislocations. (c) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved

Fermi surface of MoO2 studied by angle-resolved photoemission spectroscopy, de Haas-van Alphen measurements, and electronic structure calculations

A comprehensive study of the electronic properties of monoclinic MoO2 from both an experimental and a theoretical point of view is presented. We focus on the investigation of the Fermi body and the band structure using angle resolved photoemission spectroscopy, de Haas-van Alphen measurements, and electronic structure calculations. For the latter, the new full-potential augmented spherical wave (ASW) method has been applied. Very good agreement between the experimental and theoretical results is found. In particular, all Fermi surface sheets are correctly identified by all three approaches. Previous controversies concerning additional hole-like surfaces centered around the Z- and B-point could be resolved; these surfaces were an artefact of the atomic-sphere approximation used in the old calculations. Our results underline the importance of electronic structure calculations for the understanding of MoO2 and the neighbouring rutile-type early transition-metal dioxides. This includes the low-temperature insulating phases of VO2 and NbO2, which have crystal structures very similar to that of molybdenum dioxide and display the well-known prominent metal-insulator transitions.Comment: 17 pages, 21 figures, more information at http://www.physik.uni-augsburg.de/~eyert

GUTs in Type IIB Orientifold Compactifications

We systematically analyse globally consistent SU(5) GUT models on intersecting D7-branes in genuine Calabi-Yau orientifolds with O3- and O7-planes. Beyond the well-known tadpole and K-theory cancellation conditions there exist a number of additional subtle but quite restrictive constraints. For the realisation of SU(5) GUTs with gauge symmetry breaking via U(1)_Y flux we present two classes of suitable Calabi-Yau manifolds defined via del Pezzo transitions of the elliptically fibred hypersurface P_{1,1,1,6,9}[18] and of the Quintic P_{1,1,1,1,1}[5], respectively. To define an orientifold projection we classify all involutions on del Pezzo surfaces. We work out the model building prospects of these geometries and present five globally consistent string GUT models in detail, including a 3-generation SU(5) model with no exotics whatsoever. We also realise other phenomenological features such as the 10 10 5 Yukawa coupling and comment on the possibility of moduli stabilisation, where we find an entire new set of so-called swiss-cheese type Calabi-Yau manifolds. It is expected that both the general constrained structure and the concrete models lift to F-theory vacua on compact Calabi-Yau fourfolds.Comment: 138 pages, 9 figures; v2, v3: typos corrected, one reference adde

Gain-of-Function Variant pPro2555Arg of von Willebrand Factor Increases Aggregate Size through Altering Stem Dynamics

The multimeric plasma glycoprotein (GP) von Willebrand factor (VWF) is best known for recruiting platelets to sites of injury during primary hemostasis. Generally, mutations in the VWF gene lead to loss of hemostatic activity and thus the bleeding disorder von Willebrand disease. By employing cone and platelet aggregometry and microfluidic assays, we uncovered a platelet GPIIb/IIIa-dependent prothrombotic gain of function (GOF) for variant p.Pro2555Arg, located in the C4 domain, leading to an increase in platelet aggregate size. We performed complementary biophysical and structural investigations using circular dichroism spectra, small-angle X-ray scattering, nuclear magnetic resonance spectroscopy, molecular dynamics simulations on the single C4 domain, and dimeric wild-type and p.Pro2555Arg constructs. C4-p.Pro2555Arg retained the overall structural conformation with minor populations of alternative conformations exhibiting increased hinge flexibility and slow conformational exchange. The dimeric protein becomes disordered and more flexible. Our data suggest that the GOF does not affect the binding affinity of the C4 domain for GPIIb/IIIa. Instead, the increased VWF dimer flexibility enhances temporal accessibility of platelet-binding sites. Using an interdisciplinary approach, we revealed that p.Pro2555Arg is the first VWF variant, which increases platelet aggregate size and shows a shear-dependent function of the VWF stem region, which can become hyperactive through mutations. Prothrombotic GOF variants of VWF are a novel concept of a VWF-associated pathomechanism of thromboembolic events, which is of general interest to vascular health but not yet considered in diagnostics. Thus, awareness should be raised for the risk they pose. Furthermore, our data implicate the C4 domain as a novel antithrombotic drug target

Sustainable refurbishment of museums

A group of researchers from 5 German universities, along with several German museums, works on the development of retrofitting strategies for museum buildings. The overall aim is to provide the necessary indoor climate, as required due to preventive conservation, with a minimum energy demand. The German Maritime Museum in Bremerhaven serves as the first scheme project for the implementation and validation of their ideas.26727

Investigations on the Microstructure of an Aluminium Nitride Layer and Its Interface with the Aluminium Substrate (Part I)

In principle, the plasma nitriding of Al based substrates is a well-known process, though it remains extremely challenging from both the technological point of view and the aspect of stress loading conditions. In order to improve the latter, a duplex treatment consisting of plasma nitriding and subsequent surface remelting using electron beam technology was employed. The focus of this paper (part I) was on the characterisation of the initial microstructure after plasma nitriding. This should create the basis for a better understanding of the processes taking place or changes in the subsequent duplex treatment. This was done with the help of high-resolution imaging and analysis tools in the scanning and transmission electron microscope as well as XPS analyses. Special attention was paid to the nitriding mechanism at the interface as a function of the local microstructural constituents of the hypereutectic Al alloy substrate (Al solid solution, primary silicon, and intermetallic phases). While the main part of the nitride layer formed consisted of AlN and small fractions of pure Al in the diffusion paths, other nitrides and oxides could also be detected in the area of the interface