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Purpose: A piezoelectric vibration energy harvester (PVEH), as a self-power device that can convert ambient vibration energy into electric energy, has extensive application prospects in power supply for microsensors used in Internet of Things (IoT). How to match the ambient vibration frequencies, which are always random and broadband, is a key point to design a PVEH. In this study, a tuning fork-shaped PVEH with pendulum impact-driven enhancement is proposed for energy harvesting from broadband low-frequency vibration. Methods: The impact-driven tuning fork-shaped PVEH with adjustable mechanisms is first designed, and the working principle is introduced in detail. Dynamic equations are established, and the vibration characteristics are analyzed by comparing the results of the finite element analysis (FEA) and numerical simulation, where the natural frequencies and modes are studied, and the effects of pendulum impact-driven enhancement on the energy harvesting performance are analyzed in detail. Results: The results show that the proposed PVEH can obtain 0.6 mW and 6.4 mW output powers when the excitation frequencies are 5 Hz and 34 Hz with 0.5 g excitation amplitude and the optimum load resistance, respectively. Finally, experimental investigations are carried out to verify the energy harvesting performance, and 19 light-emitting diodes (LEDs) are lit up to assess the prospective applications of the proposed impact-driven PVEH. Conclusions: The investigation demonstrates that the pendulum impact-driven could enhance the low-frequency responses, which helps the PVEH achieve the energy harvesting from broadband low-frequency ambient vibration. [ABSTRACT FROM AUTHOR]

In the complex space environment, the antenna of the running satellite may cause large amplitude nonlinear vibrations. In scientific experiments, it is difficult to simulate the state for the operation of the antenna. To study the nonlinear dynamic behaviors of the circular mesh antenna, the dynamic models and dynamic equations are established. First, the circular mesh antenna is simplified to an equivalent cylindrical shell structure. Then, the high-dimensional nonlinear dynamic equation is derived. The dynamic equations of the circular mesh antenna are discrete by the third-order Galerkin method. The breathing vibration nonlinear equations with three-degree-of-freedom are obtained. The nonlinear ordinary equations are simplified to be a topological equivalent nonlinear equation. The topological equivalent nonlinear equation under the conditions of the unperturbed and perturbed situations is analyzed, respectively. Based on the energy phase method of Haller and Wiggins, this theory for the six-dimensional system is extended and improved. The multi-pulse chaotic motion of the circular mesh antenna system is verified by the extended energy phase method. The geometric structure of the three jumping pulses in the six-dimensional phase space is described in the first time. Finally, numerical simulation is used to verify the theoretical analysis. [ABSTRACT FROM AUTHOR]

The complex natural frequencies for linear free vibrations and bifurcation and chaos for forced nonlinear vibration of axially moving viscoelastic plate are investigated in this paper. The governing partial differential equation of out-of-plane motion of the plate is derived by Newton's second law. The finite difference method in spatial field is applied to the differential equation to study the instability due to flutter and divergence. The finite difference method in both spatial and temporal field is used in the analysis of a nonlinear partial differential equation to detect bifurcations and chaos of a nonlinear forced vibration of the system. Numerical results show that, with the increasing axially moving speed, the increasing excitation amplitude, and the decreasing viscosity coefficient, the equilibrium loses its stability and bifurcates into periodic motion, and then the periodic motion becomes chaotic motion by period-doubling bifurcation. [ABSTRACT FROM AUTHOR]

One of the major inconveniences encountered in sleep studies is the time-consuming labor involved in electroencephalography (EEG) analysis. The choice of epoch duration is of prime importance and is highly related to the outcome of EEG analysis. This study was designed to find the optimal EEG epoch duration that accurately reveals the sleep-wake profiles of animals and relieve researchers of the laborious analysis of rodent sleep-wake parameters. We analyzed mouse and rat EEG signals with commonly used epoch durations (4, 8, 10, 20, and 30 s) and compared the resulting sleep-wake profiles in terms of amounts of sleep and wakefulness, number and duration of episodes, number of sleep-wake stage transitions, and EEG power spectra. There were no statistical differences in the amount and EEG power density of wakefulness, rapid eye movement (REM) and non-REM sleep among the 5 epoch durations we used. However, the shorter the epoch, the more numerous the stage transitions and the larger the episode number. The purpose of an experiment should be a main criterion for determining the optimal epoch length for the experiment. When the amount of each stage and power density of EEG signals are desired, a 30-s epoch duration is appropriate, to save time; and the results obtained are no different from those found by analysis of other epoch durations. If stage transition and duration and number of episodes are to be considered, a 4-s epoch duration is suggested as the best choice for analysis. [ABSTRACT FROM AUTHOR]

The surface structure and morphology of Pt catalysts supported on various oxides were studied by HREM profile imaging. An unstable Ti oxide overlayer and a stable crystalline monolayer on TiO supported Pt particles were observed after HTR at 923K. The overlayers could explain the SMSI in Pt/TiO. [ABSTRACT FROM AUTHOR]