Biomechanics of human fetal hearts with critical aortic stenosis

Critical aortic stenosis (AS) of the fetal heart causes a drastic change in the cardiac biomechanical environment. Consequently, a substantial proportion of such cases will lead to a single-ventricular birth outcome. However, the biomechanics of the disease is not well understood. To address this, we performed Finite Element (FE) modelling of the healthy fetal left ventricle (LV) based on patient-specific 4D ultrasound imaging, and simulated various disease features observed in clinical fetal AS to understand their biomechanical impact. These features included aortic stenosis, mitral regurgitation (MR) and LV hypertrophy, reduced contractility, and increased myocardial stiffness. AS was found to elevate LV pressures and myocardial stresses, and depending on severity, can drastically decrease stroke volume and myocardial strains. These effects are moderated by MR. AS alone did not lead to MR velocities above 3 m/s unless LV hypertrophy was included, suggesting that hypertrophy may be involved in clinical cases with high MR velocities. LV hypertrophy substantially elevated LV pressure, valve flow velocities and stroke volume, while reducing LV contractility resulted in diminished LV pressure, stroke volume and wall strains. Typical extent of hypertrophy during fetal AS in the clinic, however, led to excessive LV pressure and valve velocity in the FE model, suggesting that reduced contractility is typically associated with hypertrophy. Increased LV passive stiffness, which might represent fibroelastosis, was found to have minimal impact on LV pressures, stroke volume, and wall strain. This suggested that fibroelastosis could be a by-product of the disease progression and does not significantly impede cardiac function. Our study demonstrates that FE modelling is a valuable tool for elucidating the biomechanics of congenital heart disease and can calculate parameters which are difficult to measure, such as intraventricular pressure and myocardial stresses

Noise spectroscopy of nanowire structures: fundamental limits and application aspects

Nanowires (NWs) have recently emerged as a new class of materials demonstrating unique properties which may completely differ from their bulk counterparts. The main aim of this work is to give an overview of results on noise and fluctuation phenomena in NW-based structures. We emphasize that noise is one of the main parameters, which determines the characteristics of the device structures and sets the fundamental limits of the working principles and operation regimes of NWs as key electronic elements, including field-effect transistors (FETs). We review the studies focusing on the understanding of noise sources and the main application aspects of noise spectroscopy. Noise application aspects will provide information about the performance of core–shell NW structures, the gate-coupling effect and its advantages for detection of the useful signal with prospects to extract it from the noise level, random telegraph signal as a useful tool for enhanced sensitivity, novel components of noise reflecting dielectric polarization fluctuation processes and fluctuation phenomena as a sensitive tool for molecular charge dynamics in NW FETs. Moreover, noise spectroscopy assists understanding of electronic transport regimes and effects, transport peculiarities in topological materials and aspects reflecting Majorana bound states. Thus noise in NWs on the basis of Si, Ge, Si/Ge, GaAs, InAs, InGaAs, Au, GaAs/AlGaAs, GaAsSb, SnO2, GaN, ZnO, CuO, In2O3 and AlGaN/GaN materials reflects a great variety of phenomena and processes, information about their stability and reliability. It can be utilized for numerous different applications in nanoelectronics and bioelectronics