Influence of clamp-widening on the quality factor of nanomechanical silicon nitride resonators

Nanomechanical resonators based on strained silicon nitride (Si$_3$N$_4$) have received a large amount of attention in fields such as sensing and quantum optomechanics due to their exceptionally high quality factors ($Q$s). Room-temperature $Q$s approaching 1 billion are now in reach by means of phononic crystals (soft-clamping) and strain engineering. Despite great progress in enhancing $Q$s, difficulties in fabrication of soft-clamped samples limits their implementation into actual devices. An alternative means of achieving ultra-high $Q$s was shown using trampoline resonators with engineered clamps, which serves to localize the stress to the center of the resonator, while minimizing stress at the clamping. The effectiveness of this approach has since come into question from recent studies employing string resonators with clamp-tapering. Here, we investigate this idea using nanomechanical string resonators with engineered clampings similar to those presented for trampolines. Importantly, the effect of orienting the strings diagonally or perpendicularly with respect to the silicon frame is investigated. It is found that increasing the clamp width for diagonal strings slightly increases the $Q$s of the fundamental out-of-plane mode at small radii, while perpendicular strings only deteriorate with increasing clamp width. Measured $Q$s agree well with finite element method simulations even for higher-order resonances. The small increase cannot account for previously reported $Q$s of trampoline resonators. Instead, we propose the effect to be intrinsic and related to surface and radiation losses.Comment: 7 pages, 4 figure

The p53 binding protein PDCD5 is not rate-limiting in DNA damage induced cell death

The tumour suppressor p53 is an important mediator of cell cycle arrest and apoptosis in response to DNA damage, acting mainly by transcriptional regulation of specific target genes. The exact details how p53 modulates this decision on a molecular basis is still incompletely understood. One mechanism of regulation is acetylation of p53 on lysine K120 by the histone-acetyltransferase Tip60, resulting in preferential transcription of proapoptotic target genes. PDCD5, a protein with reported pro-apoptotic function, has recently been identified as regulator of Tip60-dependent p53-acetylation. In an effort to clarify the role of PDCD5 upon DNA damage, we generated cell lines in which PDCD5 expression was conditionally ablated by shRNAs and investigated their response to genotoxic stress. Surprisingly, we failed to note a rate-limiting role of PDCD5 in the DNA damage response. PDCD5 was dispensable for DNA damage induced apoptosis and cell cycle arrest and we observed no significant changes in p53 target gene transcription. While we were able to confirm interaction of PDCD5 with p53, we failed to do so for Tip60. Altogether, our results suggest a role of PDCD5 in the regulation of p53 function but unrelated to cell cycle arrest or apoptosis, at least in the cell types investigated.FP06 RTN ‘ApopTrain’Tyrolean Science FundKrebshilfe-Tyro

Ex vivo electromechanical reshaping of costal cartilage in the New Zealand white rabbit model.

Objectives/hypothesisDetermine the effective electromechanical reshaping (EMR) parameters for shape change and cell viability in the ex vivo rabbit costal cartilage model.Study designEx vivo animal study combined with computer modeling to guide electrode placement and polarity selection.MethodsRabbit costal cartilages were secured in a jig that approximated the shape of the rabbit auricle framework. Finite element modeling was used to select the initial electrode geometry, polarity, spacing, and estimate dosimetry parameters. Porcine costal cartilage was utilized to refine the selection of dosing parameters. Parametric analysis was performed to determine the effect of voltage and application time on tissue shape change. Next, rabbit rib cartilage was reshaped, varying voltage and application time to identify the lowest parameters to produce acceptable shape change mimicking native auricular cartilage. Acceptable qualitative shape change was determined on a five-point Likert scale analyzed using one-way general linear analysis of variance. Confocal microscopy with live/dead cell viability analysis determined the degree of injury and the distribution of live and dead cells.ResultsThe minimum acceptable deformation of rabbit costal cartilage was found at 4 V-3 minutes. Viability analysis of cartilage reshaped at 4 V-3 minutes demonstrates cell injury extending 2 mm away from each electrode with viable cells found between the electrodes.ConclusionsThe EMR parameters of 4 V-3 minutes demonstrates appropriate shape change producing grafts that resemble the native auricle and contains the viable cells adequate for clinical evaluation. The rabbit auricular reconstruction model using EMR is a feasible one

Radiographic findings of femoroacetabular impingement in capoeira players

Purpose. Capoeira is a Brazilian martial art that requires extreme movements of the hip to perform jumps and kicks. This study evaluated a group of capoeira players to assess the prevalence of femoroacetabular impingement (FAI) in athletes practicing this martial art. Methods. Twenty-four experienced capoeira players (14 men, 10 women) underwent a diagnostic assessment, including clinical examination and standard radiographs of the pelvis and hips. The a-angle, head–neck offset, crossover sign, acetabular index, lateral centre-edge angle, and the Tonnis grade were assessed using the radiographs. Clinical relationships for any radiographic abnormalities indicating FAI were also evaluated. Results. Four subjects (17 %) reported pain in their hips. Forty-four hips (91.7 %) had at least one radiographic sign of CAM impingement, and 22 (45.8 %) had an a-angle of more than 60_. Eighteen hips (37.5 %) had at least one sign of pincer impingement and 16 (33.3 %) a positive crossover sign. Sixteen hips (33.3 %) had mixed impingement. There was a significant positive association between having an a-angle of more than 60_ and the presence of groin pain (P = 0.002). A reduced femoral head–neck offset (P<0.001) and an increased a-angle on the anteroposterior radiograph (P = 0.008) were independently associated with a higher Tonnis grade. Conclusion. High prevalence of radiographic CAM-type FAI among these skilled capoeira players was found. In these subjects, a negative clinical correlation for an increased a-angle was also detected. Additional caution should be exercised whenever subjects with past or present hip pain engage in capoeira