Analysis of anisotropic subgrid-scale stress for coarse large-eddy simulation

This study discusses the necessity of anisotropic subgrid-scale (SGS) stress in large-eddy simulations (LESs) of turbulent shear flows using a coarse grid resolution. We decompose the SGS stress into two parts to observe the role of SGS stress in turbulent shear flows in addition to the energy transfer between grid-scale (GS or resolved scale) and SGS. One is the isotropic eddy-viscosity term, which contributes to energy transfer, and the other is the residual anisotropic term, which is separated from the energy transfer. We investigate the budget equation for GS Reynolds stress in turbulent channel flows accompanied by the SGS stress decomposition. In addition, we examine the medium and coarse filter length cases; the conventional eddy-viscosity models can fairly predict the mean velocity profile for the medium filter case and fails for the coarse filter case. The budget for GS turbulent kinetic energy shows that the anisotropic SGS stress has a negligible contribution to energy transfer. In contrast, the anisotropic stress has a large and non-dissipative contribution to the streamwise and spanwise components of GS Reynolds stress when the filter size is large. Even for the medium-size filter case, the anisotropic stress contributes positively to the budget for the spanwise GS Reynolds stress. Spectral analysis of the budget reveals that the positive contribution is prominent at a scale consistent with the spacing of streaks in the near-wall region. Therefore, we infer that anisotropic stress contributes to the generation mechanism of coherent structures. Predicting the positive contribution of the anisotropic stress to the budget is key to further improving SGS models.Comment: 40 pages, 17 figure

Rectovaginal Fistula after Low Anterior Resection for Rectal Cancer Using a Double Stapling Technique

A 55-year-old female underwent low anterior resection for rectal cancer using a double stapling technique. She developed a rectovaginal fistula on the 9th postoperative day. She was discharged from hospital after undergoing transverse colostomy, and 5 months later she underwent transvaginal repair of the rectovaginal fistula. She subsequently had an uneventful recovery. The leading cause of this complication is involvement of the posterior wall of the vagina in the staple line when firing the circular stapler. Transvaginal repair with a diverting stoma for rectovaginal fistula is a safe, minimally invasive and effective method

Imaging the decay of quantized vortex rings to decipher quantum dissipation

Like many quantum fluids, superfluid helium-4 (He II) can be considered as a mixture of two miscible fluid components: an inviscid superfluid and a viscous normal fluid consisting of thermal quasiparticles [1]. A mutual friction between the two fluids can emerge due to quasiparticles scattering off quantized vortex lines in the superfluid [2]. This quantum dissipation mechanism is the key for understanding various fascinating behaviors of the two-fluid system [3,4]. However, due to the lack of experimental data for guidance, modeling the mutual friction between individual vortices and the normal fluid remains an unsettled topic despite decades of research [5-10]. Here we report an experiment where we visualize the motion of quantized vortex rings in He II by decorating them with solidified deuterium tracer particles. By examining how the rings spontaneously shrink and accelerate, we provide unequivocal evidences showing that only a recent theory [9] which accounts for the coupled motion of the two fluids with a self-consistent local friction can reproduce the observed ring dynamics. Our work eliminates long-standing ambiguities in our theoretical description of the vortex dynamics in He II, which will have a far-reaching impact since similar mutual friction concept has been adopted for a wide variety of quantum two-fluid systems, including atomic Bose-Einstein condensates (BECs) [11,12], superfluid neutron stars [13-15], and gravity-mapped holographic superfluid [16,17].Comment: 10 pages, 6 figure

Intubation during a medevac flight: safety and effect on total prehospital time in the helicopter emergency medical service system

Introduction The Helicopter Emergency Medical Service (HEMS) commonly intubates patients who require advanced airway support prior to takeoff. In-flight intubation (IFI) is avoided because it is considered difficult due to limited space, difficulty communicating, and vibration in flight. However, IFI may shorten the total prehospital time. We tested whether IFI can be performed safely by the HEMS. Methods We conducted a retrospective cohort study in adult patients transported from 2010 to 2017 who received prehospital, non-emergent intubation from a single HEMS. We divided the cohort in two groups, patients intubated during flight (flight group, FG) and patients intubated before takeoff (ground group, GG). The primary outcome was the proportion of successful intubations. Secondary outcomes included total prehospital time and the incidence of complications. Results We analyzed 376 patients transported during the study period, 192 patients in the FG and 184 patients in the GG. The intubation success rate did not differ between the two groups (FG 189/192 [98.4%] vs. GG 179/184 [97.3%],p = 0.50). There were also no differences in hypoxia (FG 4/117 [3.4%] vs. GG 4/95 [4.2%],p = 1.00) or hypotension (FG 6/117 [5.1%] vs. GG 5/95 [5.3%],p = 1.00) between the two groups. Scene time and total prehospital time were shorter in the FG (scene time 7 min vs. 14 min,p < 0.001; total prehospital time 33.5 min vs. 40.0 min,p < 0.001). Conclusions IFI was safely performed with high success rates, similar to intubation on the ground, without increasing the risk of hypoxia or hypotension. IFI by experienced providers shortened transportation time, which may improve patient outcomes