Erzwungene Verständigung? Die Kommission der Historiker der DDR und der Volksrepublik Polen 1956-1990Coerced Agreement? The Historical Commission of the GDR and the People´s Republic of Poland 1956-1990

Von 1956 bis 1990 unterhielten die DDR und die Volksrepublik Polen eine Historikerkommission über die gemeinsame deutsch-polnische Vergangenheit, angesichts des zurückliegenden Krieges ein überaus diffiziler Gegenstand. Im Rahmen oktroyierter staatssozialistischer Systeme fand sie zudem unter ungünstigen Bedingungen statt. Bedacht mit dem Auftrag zur positiven Traditionsstiftung, hatte die Kommission ein weites Spannungsfeld zwischen alter Erbfeindschaft und neuer Völkerfreundschaft zu überbrücken. Dabei zeigte sich rasch, dass beide Seiten ihre gemeinsame Beziehungsgeschichte ganz unterschiedlich interpretierten: Die Deutschen beriefen sich auf einen orthodoxen Klassenstandpunkt, der es gestattete, den deutschen Faschismus und Imperialismus einer Klasse der Monopolbourgeoisie und nicht einem Volk den Deutschen anzulasten. Dagegen blieben die Polen einer Sichtweise verpflichtet, die positive und negative historische Kräfte national konnotierte und ein reaktionäres Deutschland (Preußentum, Faschismus) mit einem progressiven polnischen Kampf um Unabhängigkeit und nationale Selbstbehauptung kontrastierte. Die daraus hervorgehenden Diskussionen gestatten Einsichten in die Mechanismen selektiven Erinnerns und Rückschlüsse auf die Möglichkeiten und Grenzen gebundener Geschichtswissenschaft im staatssozialistischen Kontex

Comparison of the Internal Fatigue Crack Initiation and Propagation Behavior of a Quenched and Tempered Steel with and without a Thermomechanical Treatment

Previous studies have shown that a thermomechanical treatment (TMT) consisting of cyclic plastic deformation in the temperature range of dynamic strain aging can increase the fatigue limit of quenched and tempered steels by strengthening the microstructure around non-metallic inclusions. This study considers the influence of a TMT on the shape, size and position of crack-initiating inclusions as well as on the internal crack propagation behavior. For this, high cycle fatigue tests on specimens with and without TMT were performed at room temperature at a constant stress amplitude. The TMT increased the average lifetime by about 40%, while there was no effect of the TMT on the form or size of critical inclusions. Surprisingly, no correlation between inclusion size and lifetime could be found for both specimen types. There is also no correlation between inclusion depth and lifetime, which means that the crack propagation stage covers only a small portion of the overall lifetime. The average depth of critical inclusions is considerably higher for TMT specimens indicating that the strengthening effect of the TMT is more pronounced for near-surface inclusions. Fisheye fracture surfaces around the critical inclusions could be found on all tested specimens. With increasing fisheye size, a transition from a smooth to a rather rough and wavy fracture surface could be observed for both specimen types

Schädigung und Lebensdauer von Nickelbasislegierungen unter thermisch-mechanischer Ermüdungsbeanspruchung bei verschiedenen Phasenlagen

In dieser Arbeit wird das Verhalten zweier Nickelbasislegierungen unter thermisch-mechanischer Ermüdungsbeanspruchung bei verschiedenen Phasenlagen zwischen mechanischer Dehnung und Temperatur untersucht. Der Schwerpunkt liegt auf der Charakterisierung der Mikrostrukturen sowie der Schädigungsmechanismen in Abhängigkeit der Phasenlage. Aufbauend auf den Erkenntnissen wird ein Modell für die Lebensdauerbeschreibung vorgeschlagen

Length of pressure-controlled reperfusion is critical for reducing ischaemia-reperfusion injury in an isolated rabbit lung model

<p>Abstract</p> <p>Background</p> <p>Ischaemia-reperfusion injury is still a major problem after lung transplantation. Several reports describe the benefits of controlled graft reperfusion. In this study the role of length of the initial pressure-controlled reperfusion (PCR) was evaluated in a model of isolated, buffer-perfused rabbit lungs.</p> <p>Methods</p> <p>Heart-lung blocks of 25 New Zealand white rabbits were used. After measurement of baseline values (haemodynamics and gas exchange) the lungs were exposed to 120 minutes of hypoxic warm ischaemia followed by repeated measurements during reperfusion. Group A was immediately reperfused using a flow of 100 ml/min whereas groups B, C and D were initially reperfused with a maximum pressure of 5 mmHg for 5, 15 or 30 minutes, respectively. The control group had no period of ischaemia or PCR.</p> <p>Results</p> <p>Uncontrolled reperfusion (group A) caused a significant pulmonary injury with increased pulmonary artery pressures (PAP) and pulmonary vascular resistance and a decrease in oxygen partial pressure (PO₂), tidal volume and in lung compliance. All groups with PCR had a significantly higher PO₂for 5 to 90 min after start of reperfusion. At 120 min there was also a significant difference between group B (264 ± 91 mmHg) compared to groups C and D (436 ± 87 mmHg; 562 ± 20 mmHg, p < 0.01). All PCR groups showed a significant decrease of PAP compared to group A.</p> <p>Conclusion</p> <p>Uncontrolled reperfusion results in a severe lung injury with rapid oedema formation. PCR preserves pulmonary haemodynamics and gas exchange after ischaemia and might allows for recovery of the impaired endothelial function. 30 minutes of PCR provide superior results compared to 5 or 15 minutes of PCR.</p

Towards detecting, characterizing and rating of road class errors in crowd-sourced road network databases

OpenStreetMap (OSM), with its global coverage and Open Database License, has recently gained popularity. Its quality is adequate for many applications, but since it is crowd-sourced, errors remain an issue. Errors in associated tags of the road network, for example, are impacting routing applications. Particularly road classification errors often lead to false assumptions about capacity, maximum speed, or road quality which could then result in detours for routing applications. This study aims at finding potential classification errors automatically, which can then be checked and corrected by a human expert. We develop a novel approach to detect road classification errors in OSM by searching for disconnected parts and gaps in different levels of a hierarchical road network. Different parameters are identified that indicate gaps in road networks. These parameters are then combined in a rating system to obtain an error probability in order to suggest possible misclassifications to a human user. The methodology is applied exemplarily for the state of New South Wales in Australia. The results demonstrate that (1) more classification errors are found at gaps than at disconnected parts and (2) the gap search enables the user to find classification errors quickly using the developed rating system that indicates an error probability. In future work, the methodology can be extended to include available tags in OSM for the rating system. The source code of the implementation is available via GitHub

Influence of a Thermo-Mechanical Treatment on the Fatigue Lifetime and Crack Initiation Behavior of a Quenched and Tempered Steel

A thermo-mechanical treatment (TMT) at the temperature of maximum dynamic strain aging has been optimized and performed on quenched and tempered steel SAE4140H (German designation: 42CrMo4) in order to improve the fatigue limit in the high cycle fatigue (HCF) and and very high cycle fatigue (VHCF) regimes. Fatigue tests, with ultimate cycle numbers of 107 and 109, have shown that the TMT can increase both the fatigue lifetime and the fatigue limit in the HCF and VHCF regimes. The increased stress intensity factors of the critical inclusions after the TMT indicate that the effect can be attributed to a stabilized microstructure around critical crack-initiating inclusions through the locking of edge dislocations by carbon atoms during the TM

Creep–Fatigue Interaction of Inconel 718 Manufactured by Electron Beam Melting

Electron beam melting of Ni-base superalloy Inconel 718 allows producing a columnar-grained microstructure with a pronounced texture, which offers exceptional resistance against high-temperature loading with severe creep–fatigue interaction arising in components of aircraft jet engines. This study considers the deformation, damage, and lifetime behavior of electron-beammelted Inconel 718 under in-phase thermomechanical fatigue loading with varying amounts of creep–fatigue interaction. Strain-controlled thermomechanical fatigue tests with equal-ramp cycles, slow–fast cycles, and dwell time cycles are conducted in the temperature range from 300 to 650 °C. Results show that both dwell time and slow–fast cycles promote intergranular cracking, gradual tensile stress relaxation, as well as precipitate dissolution and coarsening giving rise to cyclic softening. The interplay of these mechanisms leads to increased lifetimes in both dwell time and slow–fast tests compared to equal ramp tests at higher strain amplitudes. Conversely, at lower mechanical strain amplitudes, the opposite is observed. A comparison with results of conventional Inconel 718 indicates that the electron-beam-melted material exhibits superior resistance against strain-controlled loading at elevated temperatures such as thermomechanical fatigue

Influence of Shot Peening on the Isothermal Fatigue Behavior of the Gamma Titanium Aluminide Ti-48Al-2Cr-2Nb at 750 °C

One possibility to improve the fatigue life and strength of metallic materials is shot peening. However, at elevated temperatures, the induced residual stresses may relax. To investigate the influence of shot peening on high-temperature fatigue behavior, isothermal fatigue tests were conducted on shot-peened and untreated samples of gamma TiAl 48-2-2 at 750 °C in air. The shot-peened material was characterized using EBSD, microhardness, and residual stress analyses. Shot peening leads to a significant increase in surface hardness and high compressive residual stresses near the surface. Both effects may have a positive influence on lifetime. However, it also leads to surface notches and tensile residual stresses in the bulk material with a negative impact on cyclic lifetime. During fully reversed uniaxial tension-compression fatigue tests (R = −1) at a stress amplitude of 260 MPa, the positive effects dominate, and the fatigue lifetime increases. At a lower stress amplitude of 230 MPa, the negative effect of internal tensile residual stresses dominates, and the lifetime decreases. Shot peening leads to a transition from surface to volume crack initiation if the surface is not damaged by the shots

Soviet Nuclear Technoscience

In 1904, Frederick Soddy, who would later receive the Nobel Prize for his seminal studies in radiochemistry, speculated that the “new alchemists” who had unlocked the awe‑inspiring power of the atom would “turn wastelands green, melt the polar ice caps, and transform the planet into a friendly Garden of Eden.” But he also predicted that the state to possess the first viable atomic weapon would achieve world domination. The significance of nuclear technology, at once promising and terrible, sh..