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The opening and closing dynamics of the aortic valve (AV) has a strong influence on haemodynamics in the aortic root, and both play a pivotal role in maintaining normal physiological functions of the valve. The aim of this study was to establish a subject‐specific fluid–structure interaction (FSI) workflow capable of simulating the motion of a tricuspid healthy valve and the surrounding haemodynamics under physiologically realistic conditions. A subject‐specific aortic root was reconstructed from magnetic resonance (MR) images acquired from a healthy volunteer, whilst the valve leaflets were built using a parametric model fitted to the subject‐specific aortic root geometry. The material behaviour of the leaflets was described using the isotropic hyperelastic Ogden model, and subject‐specific boundary conditions were derived from 4D‐flow MR imaging (4D‐MRI). Strongly coupled FSI simulations were performed using a finite volume‐based boundary conforming method implemented in FlowVision. Our FSI model was able to simulate the opening and closing of the AV throughout the entire cardiac cycle. Comparisons of simulation results with 4D‐MRI showed a good agreement in key haemodynamic parameters, with stroke volume differing by 7.5% and the maximum jet velocity differing by less than 1%. Detailed analysis of wall shear stress (WSS) on the leaflets revealed much higher WSS on the ventricular side than the aortic side and different spatial patterns amongst the three leaflets. [ABSTRACT FROM AUTHOR]

In this study, a series of p-type Ag-doped PbS compounds were prepared by a vacuum melting combined with subsequent spark plasma sintering process. Ag partially occupies Pb sites acting as an electron acceptor to increase the hole concentration, and also in situ forms Ag2S nanoprecipitates at the grain boundaries which are detectable in thermal analysis and microstructural observations. The two existences of Ag both exert significant influences on the electrical transport properties. With increasing temperature, dissolution of Ag2S nanoprecipitates into the PbS matrix as interstitial Ag gradually decreases the hole concentration. Very low mobility of Ag-doped samples is unexpected at low temperatures, which indicates a strong carrier scattering. From temperature dependent mobility, it can be concluded that neutral impurity scattering (μ ∼ Ta, a = 0) dominates at low temperature (T < 200 K), and energy barrier scattering (a > 1.5) governs until lattice vibrations take over at T > 450 K (a ∼ −2.5). The complex scattering mechanisms at T < 450 K in Ag-doped samples should be originated from the multiple existences of Ag (Ag+, interstitial Ag, Ag2S nanoprecipitates). In particular, Ag doping increases the high temperature electrical conductivity, giving rise to an enhanced power factor of ∼0.8 × 10−3 W m−1 K−2 at 870 K for the 1.5 at% Ag-doped sample. Benefiting from the improved power factor and low lattice thermal conductivity originating from strong lattice anharmonicity, a doubled ZT value of ∼0.6 can be achieved for Pb0.985Ag0.015S in comparison to that of pristine PbS. [ABSTRACT FROM AUTHOR]

As an important means of treating heart failure (HF), cardiac assist device has been widely used in clinic. This paper reviews the application status, existing problems and future development trend of cardiac assist devices, including the classification of cardiac assist devices, representative research achievements and indications of the assist devices. It also summarizes the biomechanical indexes of the heart and the new approaches and methods for treating heart failure, as well as the hemodynamic studies of cardiac assist devices in recent years. The research findings provide references for further optimization of cardiac assist device structure and clinical application of the device.