Long-Lived Coherence on a μHz Scale Optical Magnetic Quadrupole Transition

We report on the coherent excitation of the ultranarrow $^{1}\mathrm{S}_0$-$^{3}\mathrm{P}_2$ magnetic quadrupole transition in $^{88}\mathrm{Sr}$. By confining atoms in a state insensitive optical lattice, we achieve excitation fractions of 97(1)% and observe linewidths as narrow as 58(1) Hz. With Ramsey spectroscopy, we find coherence times of 14(1) ms, which can be extended to 266(36) ms using a spin-echo sequence. We determine the linewidth of the M2 transition to 24(7) $μ$Hz, confirming longstanding theoretical predictions. These results establish an additional clock transition in strontium and pave the way for applications of the metastable $^{3}\mathrm{P}_2$ state in quantum computing and quantum simulations.6 pages, 4 figures, 5 pages supplemental materia

Rehabilitation of Watson-Jones proximal tibial avulsion injury in elite academy level football: A report of two separate cases in one season

© 2020 Elsevier Ltd Objectives: Watson-Jones proximal tibial avulsion injuries occur more frequently in athletic and muscular adolescent males. However, they are rare and therefore infrequently described in the medical literature. Two of these injuries occurred in a Category 1 football academy in the same season within a six-month period. We have described the cases with the hope of better informing other clinicians should they encounter this injury. Methods: This case report describes the injury mechanism, surgical management and rehabilitation for the two cases [Players A and B]. Outcomes measures including player speed, agility and power were compared with scores from players of the same age group at the time of injury in the Premier League academies. Risk factors are also discussed. Results: Both players were managed surgically, initially. Player B had the surgical fixation removed during rehabilitation. Player A still has the fixation in situ. Post-surgery, player A returned to full play at thirty-two weeks and thirty-eight weeks for player B. No critical incidents occurred during rehabilitation. Conclusion: Watson-Jones avulsion fractures, although rare, can be managed successfully. Athletes can achieve a successful return to play at their previous level

Very high cycle fatigue of high-strength steels: Crack initiation by FGA formation investigated at artificial defects

AbstractIt is well known, that high-strength steels do not show a classical fatigue limit and failure occurs still after 107 cycles. The reason for this late failure is that the fatigue properties in the long life region are strongly affected by non-metallic inclusions inside the material (Murakami et al. (1989)). After VHCF a characteristic fine granular area, or short FGA, can be observed at the fracture surface. The FGA formation is responsible for the late initiation of a propagable long crack (Grad et al. (2012); Sakai et al. (2002)). In recent years a lot of research was carried out to reveal the mechanism responsible for the crack initiation by FGA formation (Grad et al. (2012); Murakami et al. (1999); Sakai, Kokubu, et al. (2015); Shiozawa et al. (2008)). Multiple different theories exist in literature trying to explain VHCF failure. Because of its occurrence solely below the surface by now only the fracture surface could be observed after the failure occurred. This makes it impossible to gain a full understanding of the mechanisms leading to failure. Consequently all proposed mechanisms remain unprovable theories, up to now.In order to further investigate FGA formation we have simulated the VHCF-failure at artificial surface defects. According to literature the absence of any environment seems to be crucial for VHCF subsurface failure by FGA formation in high-strength steels (Billaudeau et al. (2004)). Thus, fatigue tests were performed in ultra-high vacuum to simulate subsurface condition at surface defects. Thereby the FGA formation can be reproduced at the surface and gets observable quasi in situ. Microstructural investigations were carried out with transmission electron microscopy inside the FGA at artificial defects. These measurements show the comparability of the resulting microstructure at artificial defects with the FGA microstructure after failure at subsurface inclusions. Therefore, it is possible to gain new insights into FGA formation gained with the use of artificial defects. Thereby fatigue test with artificial defect can be interrupted and enable the in situ investigation of pre-stages of FGA formation by microstructural analyses with transmission electron microscopy. With this testing procedure it should be possible to enhance the knowledge of the very high cycle fatigue in high-strength steels and the associated failure mechanisms