ABSTRACT
We review the efforts made by the scientific community in more than seventy years to elucidate the behaviour of concentration fluctuations arising from localized atmospheric releases of dynamically passive and non-reactive scalars. Concentration fluctuations are relevant in many fields including the evaluation of toxicity, flammability, and odour nuisance. Characterizing concentration fluctuations requires not just the mean concentration but also at least the variance of the concentration in the location of interest. However, for most purposes the characterization of the concentration fluctuations requires knowledge of the concentration probability density function (PDF) in the point of interest and even the time evolution of the concentration. We firstly review the experimental works made both in the field and in the laboratory, and cover both point sources and line sources. Regarding modelling approaches, we cover analytical, semi-analytical, and numerical methods. For clarity of presentation we subdivide the models in two groups, models linked to a transport equation, which usually require a numerical resolution, and models mainly based on phenomenological aspects of dispersion, often providing analytical or semi-analytical relations. The former group includes: large-eddy simulations, Reynolds-averaged Navier-Stokes methods, two-particle Lagrangian stochastic models, PDF transport equation methods, and heuristic Lagrangian single-particle methods. The latter group includes: fluctuating plume models, semi-empirical models for the concentration moments, analytical models for the concentration PDF, and concentration time-series models. We close the review with a brief discussion highlighting possible useful additions to experiments and improvements to models.
ABSTRACT
OBJECTIVES: Transapical off-pump NeoChord repair is a novel minimally invasive surgical procedure to treat degenerative mitral valve regurgitation. The aim was to evaluate 1-year clinical results of the NeoChord procedure in a consecutive cohort of patients. METHODS: Between February 2013 and July 2016, 213 patients were enrolled in the NeoChord Independent International Registry. All patients presented severe mitral regurgitation due to flail/prolapse of 1 or both leaflets, and they all completed postoperative echocardiographic assessment up to 1 year. We identified the primary end point as composed of procedural success, freedom from mortality, stroke, reintervention, recurrence of severe mitral regurgitation, rehospitalization and decrease of at least 1 New York Heart Association functional class at 1-year follow-up. We also compared outcomes according to the anatomical classification (Type A: isolated central posterior leaflet disease; Type B: posterior multisegment disease; Type C: anterior, bileaflet, paracommissural disease with/without leaflet/annular calcifications). RESULTS: The median age was 68 years (interquartile range 56-77), and the median EuroSCORE II was 1.05% (interquartile range 0.67-1.76). The number of Type A, B and C patients was 82 (38.5%), 98 (46%) and 33 (15.5%), respectively. Procedural success was achieved in 206 (96.7%) patients. At 1-year follow-up, overall survival was 98 ± 1%. Composite end point was achieved in 84 ± 2.5% for the overall population and 94 ± 2.6%, 82.6 ± 3.8% and 63.6 ± 8.4% in Type A, Type B and Type C patients, respectively (P < 0.0001). CONCLUSIONS: These results demonstrate that the NeoChord procedure is safe, effective and reproducible. Clinical and echocardiographic efficacy is maintained up to 1 year with significant differences among the anatomical groups. Specific anatomical selection criteria are necessary to achieve stable results.
