Thermally activated processes in materials probed by nanoindentation - challenges, solutions, and insights

Nanoindentation experiments are widely used for assessing the local mechanical properties of materials. In recent years some new exciting developments were established for also analyzing thermally activated processes during deformation using indentation based techniques, namely nanoindentation strain rate jump and nanoindentation long term creep tests. For these different methods, control of the indenter tip movement as well as determination of the correct contact conditions are hugely important to assure reliable data. In fact, long term nanoindentation tests are prone to be strongly influenced by thermal drift, starting at room temperature but even more intensified for elevated temperatures. This talk will first focus on experimental issues and challenges, but also solutions during advanced nanoindentation testing to overcome thermal drift influences, as demonstrated for fused silica and ultra-fine grained (ufg) Au. Special focus will be on high temperature testing, different testing methodologies will be described, and it will be demonstrated how distinct indentation time and indentation depths related errors influence the basic results. In the second part different results on single crystal (sx) and ufg Cr but also on the intermetallic phase Mg17Al12 are presented. For Mg17Al12, it was observed that the deformation behavior, especially in terms of thermally activated processes, is significantly changing over temperature. While at room temperature up to 125°C deformation is dominated by jerky flow and a slight negative strain-rate sensitivity due to dislocation pinning and the Portevin - Le Chatelier effect, overcoming 150°C the material behaves remarkably different. In this regime the indentation data show significant ductile deformation behavior with large pile-up formation and a pronounced strain rate sensitivity in the superplastic regime, where the deformation is sustained by dislocation glide and climb. Sx and ufg Cr also show significant changes in deformation behavior with temperature. At ambient conditions, both microstructures show an enhanced strain-rate sensitivity due to the large thermally activated component in the flow stress. Overcoming the materials specific temperature Tc (~150°C for Cr) the behavior changes. For sx Cr the apparent strain-rate sensitivity diminishes completely, while for the ufg state the strain-rate sensitivity increases due to the increased importance of dislocation – grain boundary interactions paired with a change in the dominating deformation mechanism

Examiner effect on the objective structured clinical exam – a study at five medical schools

Background: The Objective Structured Clinical Examination (OSCE) is increasingly used at medical schools to assess practical competencies. To compare the outcomes of students at different medical schools, we introduced standardized OSCE stations with identical checklists. Methods: We investigated examiner bias at standardized OSCE stations for knee- and shoulder-joint examinations, which were implemented into the surgical OSCE at five different medical schools. The checklists for the assessment consisted of part A for knowledge and performance of the skill and part B for communication and interaction with the patient. At each medical faculty, one reference examiner also scored independently to the local examiner. The scores from both examiners were compared and analysed for inter-rater reliability and correlation with the level of clinical experience. Possible gender bias was also evaluated. Results: In part A of the checklist, local examiners graded students higher compared to the reference examiner; in part B of the checklist, there was no trend to the findings. The inter-rater reliability was weak, and the scoring correlated only weakly with the examiner’s level of experience. Female examiners rated generally higher, but male examiners scored significantly higher if the examinee was female. Conclusions: These findings of examiner effects, even in standardized situations, may influence outcome even when students perform equally well. Examiners need to be made aware of these biases prior to examining

Dimethylarginine Dimethylaminohydrolase-1 Transgenic Mice Are Not Protected from Ischemic Stroke

Methylated arginines are endogenous analogues of L-arginine, the substrate for nitric oxide (NO) synthase. Asymmetric dimethylarginine (ADMA) interferes with NO formation, causing endothelial dysfunction. ADMA is a predictor of cardiovascular events and mortality in humans. It is eliminated primarily by enzymatic activity of dimethylarginine dimethylaminohydrolase (DDAH).We investigated whether human DDAH-1 (hDDAH-1) transgenicity protects from ischemic tissue damage in temporary middle cerebral artery occlusion (tMCAO) in mice. Infarct sizes did not significantly differ between hDDAH-1 transgenic (TG) mice and wild-type littermates (WT). As expected, ADMA plasma concentrations were significantly decreased, cerebral hDDAH expression and protein significantly increased in transgenic animals. Interestingly, neither brain tissue DDAH activity nor ADMA concentrations were different between TG and WT mice. In contrast, muscular DDAH activity was generally lower than in brain but significantly increased in TG mice.Our study demonstrates that hDDAH-1 transgenic mice are not protected from ischemic cerebral tissue damage in tMCAO. This lack of protection is due to high basal cerebral DDAH activity, which is not further increasable by transgenic overexpression of DDAH

Elementos, tipologías constructivas y rehabilitaciones en la colonia Gassol de Bítem

Estudi d'un edifici colonial emblemàtic de les terres de l'Ebre. Identificació dels elements simbólics de l'edifici, tipologies constructives, patologies en l'edifici i repercussió de les intervencions que es van dur a terme en el transcurs dels anys en l'estat actual de l'edifici

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements