Measurements of the velocity field downstream of an artificial heart valve are performed by using... more Measurements of the velocity field downstream of an artificial heart valve are performed by using particle image velocimetry (PIV) and particle tracking velocimetry (PTV). The investigated field corresponds to the region immediately downstream of the valve outlet i.e. the initial ascending part of the aorta. The aim of the paper is to investigate the evolution of the flow field in time in such inhomogeneous, anisotropic, and unsteady conditions. To do this, a high-speed video camera is used to acquire images of the seeding particles illuminated by a continuous infrared laser. high seeding density conditions are investigated using PIV to perform phase-sampled Eulerian averages, whereas low seeding conditions are used to determine particle trajectories and Lagrangian statistics using PTV. Both are needed for the complete description of the magnitude and duration of the stress on blood cells. The following features are described: The very high inhomogeneity and unsteadiness of the phenomenon The presence of large scale vortices within the field especially in the sinuses of Valsalva and in the wake of the valve leaflets The strong stress and strain rates at the jet–wake interface downstream of the leaflets and close to large-scale vortices The non-negligible time spent by fluid particles in some of the high stress and strain regions
A three-dimensional, realistic model of an aortic mechanical heart valve and Valsalva sinuses was... more A three-dimensional, realistic model of an aortic mechanical heart valve and Valsalva sinuses was developed to predict, by means of a numerical time dependent simulation, the flow field during a fraction of the systolic period. The numeric simulation was performed upon a model of valve similar to a Carbomedics 27 mm placed in a physiologic aortic root shaped model, in which no symmetry planes were exploited to reach a more realistic level. Input data for the simulation have been acquired during an experimental session on the same valve, according to the guidelines of testing protocol for prosthetic heart valves. Flow was assumed to be Newtonian and laminar at low regime and the leaflets fixed in the fully open position. The forward flow of the systolic phase was investigated, and a comparison with experimental results was performed at peak systole, the most representative point of the cardiac cycle. The results of this simulation furnished a reasonable indication (in terms of fluid dynamics) parameters downstream of the prosthetic device, especially in Valsalva sinuses, the role of which is proven to affect the valve's performance.
High-quality single-crystal diamond films, homoepitaxially grown by microwave chemical vapor depo... more High-quality single-crystal diamond films, homoepitaxially grown by microwave chemical vapor deposition, have been used to produce diamond-based photodetectors. Such devices were tested over a very wide spectral range, from the extreme ultraviolet (UV) (20 nm) up to the near IR region (2400 nm). An optical parametric oscillator tunable laser was used to investigate the 210-2400 nm spectral range in pulse mode. In this region, the spectral response shows a UV to visible contrast of about 6 orders of magnitude. A time response shorter than 5 ns, i.e., the laser pulse duration, was observed. By integrating the pulse shape, a minor slow component was evidenced, which can be explained in terms of trapping-detrapping effects. Extreme UV gas sources and a toroidal grating vacuum monochromator were used to measure the device response down to 20 nm in continuous mode. In particular, the extreme UV He spectrum was measured and the He II m, 30.4 nmand He I 58.4 nm emission lines were clearly detected. The measured time response of 0.2 s is totally due to the instrumental readout time constants. In both experimental setups an extremely good stability and reproducibility of the device response were obtained, whereas no persistent photoconductivity nor undesirable pumping effects were observed.
Defects limiting the movement of charge carriers in polycrystalline chemical vapor deposition (CV... more Defects limiting the movement of charge carriers in polycrystalline chemical vapor deposition (CVD) diamond films are located within the grains or in grain boundaries. Their geometrical distribution in the sample is different and is usually unknown. We present here a method to quantitatively evaluate the concentration and distribution of in-grain and grain-boundary located active carrier traps. Since the impact of
Measurements of the velocity field downstream of an artificial heart valve are performed by using... more Measurements of the velocity field downstream of an artificial heart valve are performed by using particle image velocimetry (PIV) and particle tracking velocimetry (PTV). The investigated field corresponds to the region immediately downstream of the valve outlet i.e. the initial ascending part of the aorta. The aim of the paper is to investigate the evolution of the flow field in time in such inhomogeneous, anisotropic, and unsteady conditions. To do this, a high-speed video camera is used to acquire images of the seeding particles illuminated by a continuous infrared laser. high seeding density conditions are investigated using PIV to perform phase-sampled Eulerian averages, whereas low seeding conditions are used to determine particle trajectories and Lagrangian statistics using PTV. Both are needed for the complete description of the magnitude and duration of the stress on blood cells. The following features are described: The very high inhomogeneity and unsteadiness of the phenomenon The presence of large scale vortices within the field especially in the sinuses of Valsalva and in the wake of the valve leaflets The strong stress and strain rates at the jet–wake interface downstream of the leaflets and close to large-scale vortices The non-negligible time spent by fluid particles in some of the high stress and strain regions
A three-dimensional, realistic model of an aortic mechanical heart valve and Valsalva sinuses was... more A three-dimensional, realistic model of an aortic mechanical heart valve and Valsalva sinuses was developed to predict, by means of a numerical time dependent simulation, the flow field during a fraction of the systolic period. The numeric simulation was performed upon a model of valve similar to a Carbomedics 27 mm placed in a physiologic aortic root shaped model, in which no symmetry planes were exploited to reach a more realistic level. Input data for the simulation have been acquired during an experimental session on the same valve, according to the guidelines of testing protocol for prosthetic heart valves. Flow was assumed to be Newtonian and laminar at low regime and the leaflets fixed in the fully open position. The forward flow of the systolic phase was investigated, and a comparison with experimental results was performed at peak systole, the most representative point of the cardiac cycle. The results of this simulation furnished a reasonable indication (in terms of fluid dynamics) parameters downstream of the prosthetic device, especially in Valsalva sinuses, the role of which is proven to affect the valve's performance.
High-quality single-crystal diamond films, homoepitaxially grown by microwave chemical vapor depo... more High-quality single-crystal diamond films, homoepitaxially grown by microwave chemical vapor deposition, have been used to produce diamond-based photodetectors. Such devices were tested over a very wide spectral range, from the extreme ultraviolet (UV) (20 nm) up to the near IR region (2400 nm). An optical parametric oscillator tunable laser was used to investigate the 210-2400 nm spectral range in pulse mode. In this region, the spectral response shows a UV to visible contrast of about 6 orders of magnitude. A time response shorter than 5 ns, i.e., the laser pulse duration, was observed. By integrating the pulse shape, a minor slow component was evidenced, which can be explained in terms of trapping-detrapping effects. Extreme UV gas sources and a toroidal grating vacuum monochromator were used to measure the device response down to 20 nm in continuous mode. In particular, the extreme UV He spectrum was measured and the He II m, 30.4 nmand He I 58.4 nm emission lines were clearly detected. The measured time response of 0.2 s is totally due to the instrumental readout time constants. In both experimental setups an extremely good stability and reproducibility of the device response were obtained, whereas no persistent photoconductivity nor undesirable pumping effects were observed.
Defects limiting the movement of charge carriers in polycrystalline chemical vapor deposition (CV... more Defects limiting the movement of charge carriers in polycrystalline chemical vapor deposition (CVD) diamond films are located within the grains or in grain boundaries. Their geometrical distribution in the sample is different and is usually unknown. We present here a method to quantitatively evaluate the concentration and distribution of in-grain and grain-boundary located active carrier traps. Since the impact of
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Papers by Antonio Balducci