TY - JOUR A1 - Müller, B. R. A1 - Cooper, R. C. A1 - Lange, A. A1 - Kupsch, Andreas A1 - Wheeler, M. A1 - Hentschel, M. P. A1 - Staude, A. A1 - Pandey, A. A1 - Shyam, A. A1 - Bruno, Giovanni T1 - Stress-induced microcrack density evolution in beta-eucryptite ceramics BT - experimental observations and possible route to strain hardening JF - Acta materialia N2 - In order to investigate their microcracking behaviour, the microstructures of several beta-eucryptite ceramics, obtained from glass precursor and cerammed to yield different grain sizes and microcrack densities, were characterized by laboratory and synchrotron x-ray refraction and tomography. Results were compared with those obtained from scanning electron microscopy (SEM). In SEM images, the characterized materials appeared fully dense but computed tomography showed the presence of pore clusters. Uniaxial tensile testing was performed on specimens while strain maps were recorded and analyzed by Digital Image Correlation (DIC). X-ray refraction techniques were applied on specimens before and after tensile testing to measure the amount of the internal specific surface (i.e., area per unit volume). X-ray refraction revealed that (a) the small grain size (SGS) material contained a large specific surface, originating from the grain boundaries and the interfaces of TiO2 precipitates; (b) the medium (MGS) and large grain size (LGS) materials possessed higher amounts of specific surface compared to SGS material due to microcracks, which decreased after tensile loading; (c) the precursor glass had negligible internal surface. The unexpected decrease in the internal surface of MGS and LGS after tensile testing is explained by the presence of compressive regions in the DIC strain maps and further by theoretical arguments. It is suggested that while some microcracks merge via propagation, more close mechanically, thereby explaining the observed X-ray refraction results. The mechanisms proposed would allow the development of a strain hardening route in ceramics. KW - Beta-eucryptite KW - Microcracked ceramics KW - X-ray refraction KW - Tensile load KW - Strain hardening Y1 - 2017 U6 - https://doi.org/10.1016/j.actamat.2017.10.030 SN - 1359-6454 SN - 1873-2453 VL - 144 SP - 627 EP - 641 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Bauernschmitt, Robert A1 - Malberg, Hagen A1 - Wessel, Niels A1 - Kopp, B. A1 - Schirmbeck, E. U. A1 - Lange, R. T1 - Impairment of cardiovascular autonomic control in patients early after cardiac surgery N2 - Objective: Impairment of the baroreceptor reflex activity reflects an alteration of the autonomous regulation of the cardiovascular system and has proven to predict fatal outcome in patients after acute myocardial infarction. The following study was performed to analyse the baroreceptor sensitivity, heart rate variability and blood pressure variability in patients early after coronary surgery. Methods: Twenty-five male patients undergoing coronary artery bypass were examined in a prospective study; normal values were obtained from healthy volunteers. Arterial pressure signals were recorded from a radial artery catheter for 30 min preoperatively and in short intervals after surgery. Mechanical manipulations and pharmacological interventions were avoided during the sampling periods. Baroreflex function was calculated according to the dual sequence method, heart rate variability and blood pressure variability were calculated including nonlinear methods. Results: Initial values of the patients did not differ from healthy volunteers. The strength of baroreflex sensitivity (increase in blood pressure causing a synchronous decrease of heart rate) is low 2 It postoperatively. The number of delayed tachycardic changes of heart rate, which are caused by sympathetic activation, is only moderately reduced as compared to values obtained from healthy volunteers. Heart rate variability is widely unchanged as compared to preoperative values; blood pressure variability showed an increase of low-frequency components, again indicating sympathetic predominance. Nonlinear analyses revealed reduced system complexity at the beginning of the postoperative course. Conclusion: Obviously, there is a vagal suppression 20 h after surgery, while the sympathetic tonus works in a normal range. This unbalanced interaction of the autonomous systems is similar to findings in patients after myocardial infarction. The predictive value of these markers has to be elucidated in further clinical studies. (C) 2003 Elsevier B.V. All rights reserved Y1 - 2004 SN - 1010-7940 ER - TY - JOUR A1 - Shashev, Yury A1 - Kupsch, Andreas A1 - Lange, Axel A1 - Evsevleev, Sergei A1 - Müller, Bernd R. A1 - Osenberg, Markus A1 - Manke, Ingo A1 - Hentschel, Manfred P. A1 - Bruno, Giovanni T1 - Optimizing the visibility of X-ray phase grating interferometry JF - Materials testing : Materialprüfung ; materials and components, technology and application N2 - The performance of grating interferometers coming up now for imaging interfaces within materials depends on the efficiency (visibility) of their main component, namely the phase grating. Therefore, experiments with monochromatic synchrotron radiation and corresponding simulations are carried out. The visibility of a phase grating is optimized by different photon energies, varying detector to grating distances and continuous rotation of the phase grating about the grid lines. Such kind of rotation changes the projected grating shapes, and thereby the distribution profiles of phase shifts. This yields higher visibilities than derived from ideal rectangular shapes. By continuous grating rotation and variation of the propagation distance, we achieve 2D visibility maps. Such maps provide the visibility for a certain combination of grating orientation and detector position. Optimum visibilities occur at considerably smaller distances than in the standard setup. KW - X-ray imaging KW - grating interferometry KW - Talbot-Lau interferometer KW - X-ray refraction KW - X-ray phase contrast Y1 - 2017 U6 - https://doi.org/10.3139/120.111097 SN - 0025-5300 VL - 59 SP - 974 EP - 980 PB - Hanser CY - München ER - TY - JOUR A1 - Kupsch, Andreas A1 - Mueller, Bernd R. A1 - Lange, Axel A1 - Bruno, Giovanni T1 - Microstructure characterisation of ceramics via 2D and 3D X-ray refraction techniques JF - Journal of the European Ceramic Society N2 - 3D imaging techniques are very fashionable nowadays, and allow enormous progress in understanding ceramic microstructure, its evolution, and its link to mechanical, thermal, and transport properties. In this feature article, we report the use of a powerful, yet not so wide-spread, set of X-ray techniques based on refraction effects. X-ray refraction allows determining internal specific surface (surface per unit volume) in a non-destructive fashion, position and orientation sensitive, and with a nanometric detectability. While the techniques are limited by the X-ray absorption of the material under investigation, we demonstrate showcases of ceramics and composite materials, where understanding of process parameter influence or simply of microstructural parameters could be achieved in a way unrivalled even by high-resolution techniques such as electron microscopy or computed tomography. (C) 2016 Elsevier Ltd. All rights reserved. KW - X-ray refraction KW - Porosity KW - Specific surface KW - Crack detection KW - Composites Y1 - 2017 U6 - https://doi.org/10.1016/j.jeurceramsoc.2016.12.031 SN - 0955-2219 SN - 1873-619X VL - 37 SP - 1879 EP - 1889 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Shashev, Yury A1 - Kupsch, Andreas A1 - Lange, Axel A1 - Müller, Bernd R. A1 - Bruno, Giovanni T1 - Improving the visibility of phase gratings for Talbot-Lau X-ray imaging JF - Materials testing : Materialprüfung ; materials and components, technology and application N2 - Talbot-Lau interferometry provides X-ray imaging techniques with significant enhancement of the radiographic contrast of weakly absorbing objects. The grating based technique allows separation of absorption, refraction and small angle scattering effects. The different efficiency of rectangular and triangular shaped phase gratings at varying detector distances is investigated. The interference patterns (Talbot carpets) are modeled for parallel monochromatic radiation and measured by synchrotron radiation. In comparison to rectangular shapes of phase gratings much higher visibility is obtained for triangular shapes which yield enhanced contrast of a glass capillary test specimen. KW - Talbot-Lau interferometry KW - phase grating KW - synchrotron imaging KW - visibility KW - X-ray refraction Y1 - 2016 U6 - https://doi.org/10.3139/120.110948 SN - 0025-5300 VL - 58 SP - 970 EP - 974 PB - Hanser CY - München ER -