The hemodynamics in flexible deep veins valves is modelled by means of discrete multi-physics and an agglomeration algorithm is implemented to account for blood accrual in the flow. Computer simulations of a number of valves typologies are carried out. The results show that the rigidity and the length of the valve leaflets play a crucial role on both mechanical stress and stagnation in the flow. Rigid and short membranes may be inefficient in preventing blood reflux, but reduce the volume of stagnant blood potentially lowering the chances of thrombosis. Additionally, we also show that in venous valves, cell agglomeration is driven by stagnation rather than mechanical stress.

We propose a mesh-free and discrete (particle-based) multi-physics approach for modelling the hydrodynamics in flexible biological valves. In the first part of this study, the method is successfully validated against both traditional modelling techniques and experimental data. In the second part, it is further developed to account for the formation of solid aggregates in the flow and at the membrane surface. Simulations of various types of aggregates highlight the main benefits of discrete multi-physics and indicate the potential of this approach for coupling the hydrodynamics with phenomena such as clotting and calcification in biological valves.

Several-nanometer-size mechanical oscillators, or nanoresonators, may complement electronic and optical technologies in future terahertz devices, but they can be useful only if they can be made to have relatively light damping, that is, a quality factor as high as possible. Completely mechanically isolated nanoparticles a few nanometers in size would of course be very high-quality factor terahertz nanoresonators but would be totally unsuitable for integration into practical devices. We report the fabrication of solid-embedded nanoparticles whose natural mechanical vibrations have a usefully high quality factor. In this proof-of-concept study, a powder of approximately spherical, monodisperse 5 nm diameter ZrO2 nanoparticles is compressed to 20 GPa, whereas their mechanical vibrations are directly observed using Raman spectroscopy. Even though they are compressed very tightly in a solid, the individual nanoparticles vibrate essentially independently, being minimally coupled to their neighbors. This mechanical isolation is attributed to a subnanometer-thickness adsorbed water molecule layer, which we theoretically show to be more than sufficient to create a significant impedance mismatch. We also investigated the propagation of sound waves through the nanopowder using Brillouin scattering. The speed of long-wavelength acoustic waves is strongly dependent on the internanoparticle coupling, as revealed by the extreme variation with pressure of the speed of sound. In addition, the low-frequency Raman spectra provide an indication of the solid-state character of nanoscale ZrO2. There is a transition of the Zr–O bonds from being primarily ionic at low pressures to being primarily covalent at high pressures. Finally, a strong background in these Raman spectra is due to quasielastic scattering, which disappears at high pressure or low temperature.

The effects of surface and interface on the thermodynamics of small particles require a deeper understanding. This step is crucial for the development of models that can be used for decision-making support to design nanomaterials with original properties. On the basis of experimental results for phase transitions in compressed ZnO nanoparticles, we show the limitations of classical thermodynamics approaches (Gibbs and Landau). We develop a new model based on the Ginzburg-Landau theory that requires the consideration of several terms, such as the interaction between nanoparticles, pressure gradients, defect density, and so on. This phenomenological approach sheds light on the discrepancies in the literature as it identifies several possible parameters that should be taken into account to properly describe the transformations. For the sake of clarity and standardization, we propose an experimental protocol that must be followed during high-pressure investigations of nanoparticles in order to obtain coherent, reliable data that can be used by the scientific community.