Wave propagation visualization through ducts using the Schlieren technique for crack localization with the eSHM system.

The effective structural health monitoring (eSHM) system fully exploits the flexibility offered by the 3D printing process for analysis of the structural integrity of additive manufactured parts by integrating a smart technology inside the component. The eSHM system relies on the propagation of pressure waves through capillaries/small ducts embedded in 3D printed metallic components and allows the detection and localization of fatigue cracks. However, the nature and propagation of these waves seem to be determinant for the accuracy of the crack localization system. To achieve a better physical understanding of the propagating waves through the capillaries, computational fluid dynamics simulations are performed and compared with experimental results, obtained by Schlieren flow visualization and high-speed imaging techniques. The presence of propagating shock waves and contact discontinuities is observed in the simulations, as well as a complex reflection mechanism around the leak location. The Schlieren experiments exhibit the same wave shape behavior and complex reflection mechanism around the crack location for the contact discontinuity, and the shock tube analogy is confirmed.

The evolution of darker wings in seabirds in relation to temperature-dependent flight efficiency.

Seabirds have evolved numerous adaptations that allow them to thrive under hostile conditions. Many seabirds share similar colour patterns, often with dark wings, suggesting that their coloration might be adaptive. Interestingly, these darker wings become hotter when birds fly under high solar irradiance, and previous studies on aerofoils have provided evidence that aerofoil surface heating can affect the ratio between lift and drag, i.e. flight efficiency. However, whether this effect benefits birds remains unknown. Here, we first used phylogenetic analyses to show that strictly oceanic seabirds with a higher glide performance (optimized by reduced sink rates, i.e. the altitude lost over time) have evolved darker wings, potentially as an additional adaptation to improve flight. Using wind tunnel experiments, we then showed that radiative heating of bird wings indeed improves their flight efficiency. These results illustrate that seabirds may have evolved wing pigmentation in part through selection for flight performance under extreme ocean conditions. We suggest that other bird clades, particularly long-distance migrants, might also benefit from this effect and therefore might show similar evolutionary trajectories. These findings may also serve as a guide for bioinspired innovations in aerospace and aviation, especially in low-speed regimes.

Feasibility of using glory and speckle patterns for sizing spherical and irregular particles.

A backscattered laser light technique for sizing spherical and irregular particles is investigated in this paper. Two different interference patterns (glory and speckle), appearing in the backscatter region when a single droplet is illuminated with a laser light source, were recorded by a CCD camera. A theoretical model, based on a geometrical optics approximation, has been first developed to retrieve particle size from the analysis of these patterns and then applied to liquid and frozen water droplets with sizes ranging from 1 to 2 mm. The satisfactory agreement obtained between the theoretical model and the experimental data encourage further development of this technique.

Extracorporeal bubbles: a word of caution.

OBJECTIVES: Gaseous microemboli (GME) are a cause of neurocognitive deficit postcardiac surgery with cardiopulmonary bypass. However, the measurement of microbubbles during cardiopulmonary bypass is not easy, because blood is an opaque fluid and contains microparticles. Recently, two new microbubble counters, the Gampt BC200 and the emboli detection and classification (EDAC) quantifier, were developed for use during cardiac surgery. The accuracy of both devices was validated against industrial standards. METHODS: A clear blood analogue (30%/70% glycerol-water) was pumped, by means of a rollerpump out of a partially filled arterial line screen filter with a nominal pore size of 20 microm. Downstream the pump, all test sensors and an optical cuvette, were inserted in a vertically mounted 3/8 inch tubing. Measurements were taken at flows of 405, 1080, 3000 and 6000 ml/min. Backlight shadowgraphy and optical counting were used as industrial reference techniques for measuring size and counts. RESULTS: On average the EDAC quantifier underestimates average bubble diameter by 35+/-1%, 13+/-8%, 71+/-7% and 33+/-4% at 405, 1080, 3000 and 6000 ml/min, respectively. The Gampt BC200 has good sizing agreement at 1080 ml/min (+5+/-17%) and 3000 ml/min (+33+/-6%) but overestimates average diameter by 220+/-40% and 295+/-49% at 405 and 6000 ml/min, respectively. Both devices only partially count the number of microbubbles at higher flows. At 3 l/min the EDAC counts 38%, the Gampt 18% of total counts and at 6 l/min both the EDAC and Gampt only count 3% of total counts. CONCLUSIONS: Both the EDAC and Gampt can be used in a clinical setting for monitoring basal GME production. However, both devices have some major limitations when used for studying 'worst case' scenarios. One should take great caution when correlating measured data with neurocognitive outcome. Finally, results obtained by one device in a first study cannot be compared nor exchanged with results from the other device in a second study.