Project description:Flow patterns of a Taylor-Couette-Poiseuille flow were studied at low axial Reynolds and rotational Taylor numbers (Re ≤ 10.5, Ta ≤ 319). The radius ratio of the inner and outer cylinders was 0.804 and the ratio of the length of the annulus to the gap width was 44.5. Complete map of the studied flow regimes was elaborated. The axial and azimuthal components of the wall shear rate γ were measured at the outer fixed cylinder using a three-segment electrodiffusion probe. The components of the wall shear rate of helices have never been measured in previous investigations. Spatio-temporal description of multiple flow patterns was obtained using flow visualizations and simultaneous measurements of wall shear rate components. The flow structures include Taylor vortices, helices winding in the same direction as the base flow or in the opposite direction, helices that were stagnant or moving in the axial direction, smooth or with superposed azimuthal waves, among others. The influence of different flow structures on the wall shear stress components is discussed with and without axial base flow. It was found that the wall shear stress is a function of Ta but no significant dependence on Re was observed for the studied flow regimes and that the mean wall shear stress increases with the number of azimuthal waves. It was also noted that the ED probes provide a more detailed information about flow patterns than torque measurements and visualizations described in the literature.
Project description:ObjectivesThe Ross procedure is an attractive option for the management of aortic valve disease in paediatric patients. We reviewed our experience with the paediatric Ross procedure to determine survival and freedom from reoperation in the third decade after surgery.MethodsWe reviewed the data of 124 paediatric patients [71% male, median age at time of surgery 11.1 years (interquartile range 6-14.8 years); 63.7% bicuspid aortic valve], who underwent the Ross procedure at 2 tertiary centres from April 1991 to April 2020. The Ross-Konno procedures were performed on 14 (11.3%) patients. Deaths were cross-checked with the national health insurance database, and survival status was available for 96.8% of the patients. The median follow-up time was 12.1 years (interquartile range 3-18 years).ResultsThere were 3 early and 6 late deaths. All early deaths occurred in patients aged <1 year at the time of surgery. The 25-year survival was 90.3%. Actuarial freedom from reoperation (linearized rates in parentheses) was as follows: Autograft reoperation was 90.8% (0.48%/patient-year) and right ventricular outflow tract (RVOT) reoperation was 67% (2.07%/patient year) at 25 years. The univariable Cox-proportional hazard analysis revealed younger age at time of surgery (P < 0.001), smaller implanted valve size (P < 0.001) and the use of a xenograft rather than a homograft (P < 0.001) as predictors of RVOT reoperation. At multivariable Cox-proportional hazard analysis, only age was an independent risk factor for RVOT reoperation (P = 0.041).ConclusionsThe Ross and the Ross-Konno procedures are associated with good outcomes in paediatric patients. Reoperation of the RVOT is frequent and associated with younger age.
Project description:Rayleigh-Taylor instability (RTI) is the prominent energy mixing mechanism when heavy fluid lies on top of light fluid under the gravity. In this work, the RTI is studied in strongly coupled plasmas using two-dimensional molecular dynamics simulations. The motivation is to understand the evolution of the instability with the increasing correlation (Coulomb coupling) that happens when the average Coulombic potential energy becomes comparable to the average thermal energy. We report the suppression of the RTI due to a decrease in growth rate with increasing coupling strength. The caging effect is expected a physical mechanism for the growth suppression observed in both the exponential and the quadratic growth regimes. We also report that the increase in shielding due to background charges increases the growth rate of the instability. Moreover, the increase in the Atwood number, an entity to quantify the density gradient, shows the enhancement of the growth of the instability. The dispersion relation obtained from the molecular dynamics simulation of strongly coupled plasma shows a slight growth enhancement compared to the hydrodynamic viscous fluid. The RTI and its eventual impact on turbulent mixing can be significant in energy dumping mechanisms in inertial confinement fusion where, during the compressed phases, the coupling strength approaches unity.