Forrestdean6581

© 2020 IOP Publishing Ltd.In this paper, an approach to achieve rapid broadband discrete nanomechanical mapping of soft samples using an atomic force microscope is developed. Nanomechanical mapping (NM) is needed to investigate, for example, the dynamic evolution of the nanomechanical distribution of the sample-provided that the mapping is fast enough. The throughput of conventional NM methods, however, is inherently limited by the continuous scanning involved where the probe visits each sampling location continuously. Thus, we propose to significantly reduce the number of measurements through discrete mapping where the sample at only discrete sampling locations of interests are visited and measured. An online-searching learning-based technique is utilized to achieve rapid probe engagement and withdrawal with interaction force minimization at each sampling location. Then, a control-based nanoindentation measurement technique is used to quickly acquire the nanomechanical property at each location, over frequencies that can be chosen arbitrarily in a broad range. Finally, a decomposition-based learning approach is explored to achieve rapid probe transitions between the sampling locations. The proposed technique is demonstrated through experiments using a Polydimethylsiloxane (PDMS) sample and a PDMS-epoxy sample as examples. © 2020 IOP Publishing Ltd.OBJECTIVE Fractional calculus plays a key role in the analysis of neural dynamics. In particular, fractional calculus has been recently exploited for analyzing complex biological systems and capturing intrinsic phenomena. Also, artificial neural networks have been shown to have complex neuronal dynamics and characteristics that can be modeled by fractional calculus. Moreover, for a neural microcircuit placed on the spinal cord, fractional calculus can be employed to model the central pattern generator (CPG). However, the relation between the CPG and the motor cortex is still unclear. APPROACH In this paper, fractional-order models of the CPG and the motor cortex are built on the Van der Pol oscillator and the neural mass model (NMM), respectively. A self-consistent mean field approximation is used to construct the potential landscape of the Van der Pol oscillator. This landscape provides a useful tool to observe the 3D dynamics of the oscillator. To infer the relation of the motor cortex and CPG, the coupling model between the fractional-order Van der Pol oscillator and the NMM is built. As well, the influence of the coupling parameters on the CPG and the motor cortex is assessed. MAIN RESULTS Fractional-order NMM and coupling model of the motor cortex and the CPG are first established. The potential landscape is used to show 3D probabilistic evolution of the Van der Pol oscillator states. Detailed observations of the evolution of the system states can be made with fractional calculus. In particular, fractional calculus enables the observation of the creation of stable modes and switching between them. SIGNIFICANCE The results confirm that the motor cortex and CPG have associated modes or states that can be switched based on changes in the fractional order and the time delay. Enarodustat Fractional calculus and the potential landscape are helpful methods for better understanding of the working principles of locomotion systems. © 2020 IOP Publishing Ltd.Novel insight on the local surface properties of ZnO nanowires (NW) deposited by the evaporation-condensation method on Ag-covered Si substrates is proposed, based on the results of comparative studies by using the Scanning Electron Microscopy (SEM), X-ray photoemission spectroscopy (XPS) and Thermal Desorption Spectroscopy (TDS) methods, respectively. SEM studies showed that ZnO nanowires (nanoribbons) are mostly isolated and irregular, having the average length m and the average at the level of tens nm, respectively. Our XPS studies confirmed their evident surface non-stoichiometry, combined with strong C surface contaminations, which was related to the existence of oxygen-deficient regions. Additionally, TDS studies showed that undesired surface contaminations (including C species and hydroxyl groups) on the surface of ZnO NWs can be removed almost completely, leading to an increase of the final non-stoichiometry. Both effects are of great importance when using ZnO NWs for the detection of oxidizing gases, because the undesired C contaminations (including C-OH species) play the role of undesired barriers for the gas adsorption, especially at the low working temperature, additionally affecting the uncontrolled sensor ageing effect. Creative Commons Attribution license.We investigate in-situ laser reflectometry for measuring the axial growth rate in chemical vapor deposition of assemblies of well-aligned vertical germanium nanowires grown epitaxially on single crystal substrates. Finite Difference Frequency Domain optical simulations were performed in order to facilitate quantitative analysis and interpretation of the measured reflectivity data. The results show an insensitivity of reflected intensity oscillation period to nanowire diameter and density within the range of experimental conditions investigated. Compared to previous quantitative in-situ measurements performed on III-V nanowire arrays, which showed two distinct rate regimes, we observe a constant, steady-state wire growth rate. Furthermore, we show that the measured reflectivity decay can be used to determine the germanium nanowire nucleation time with good precision. This technique provides an avenue to monitor growth of nanowires in a variety of materials systems and growth conditions. © 2020 IOP Publishing Ltd.Floquet Majorana edge modes capture the topological features of periodically driven p-wave superconductors. We present a Kitaev chain with multiple time periodic driving terms. Our results demonstrate how multiple driving will affect Floquet bands in frequency space, leading to more robust Floquet Majorana edge modes against driving frequency ω in comparison with the single driving scenario. Meanwhile, We have proposed how to predict Majorana edge modes via the Zak phase of Floquet bands. Besides, in contrast to the cases with single driving term, where the constant phase can be gauged out by properly choosing the initial time, we have shown the relative phase between multiple driving can not be gauged out and will play a dominant role in deciding topological phase transitions. For the sake of completeness, we also investigate the high frequency limit. Analytical results on effective Hamiltonian can be obtained via Magnus expansion and relative phase induced topological transitions can be shown explicitly. © 2020 IOP Publishing Ltd.