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The quantum speed limit (QSL) represents the cornerstone of essential physical limit on the speed of evolution process in quantum mechanics. To derive the QSL for arbitrary quantum systems, here we present a geometric method, which is estiblished on the quantum brachistochrone characterized by the Riemannian metric. As an application to the complex quantum system, we consider the nonlinear Landau-Zener type two-level system, representing coherent atoms for BECs with mean-field interaction. The analytical expression of the quantum brachistochrone and population are obtained for the nonlinear system. We further derive the corresponding optimal procotol and demonstrate that the QSL is tight. We also generalize our formulation to open quantum systems., Comment: 5+3 pages,1+1 figures

We proposed a PVDF airflow sensor array based on the principle of wind cavity vibration like a whistle, which enlarged the responding amplitude of the PVDF cantilever beam. The PVDF airflow sensor array consisted of eight array units that were arranged in a circumferential configuration. Each unit consisted of a PVDF cantilever beam anchored onto a cavity structure. Circumferential array elements were used to sense wind signals from different directions. Within a certain range, the flow velocity showed a linear relationship with the response voltage. When the flow velocity was 5.32 m/s, the flow velocity error was less than 2.3%, and the flow direction error was less than 2.88%. This sensor array can calculate the airflow velocity and direction, which can assist the actuator to complete the escape movement.

Recently, the energy efficiency of sono-reactors has become one of research focuses in sono-reactors. In this work, a box type reactor with size of 125.5×44×50 mm3 is designed to research its total energy efficiency and electroacoustic efficiency at non-resonant frequency of 21 kHz; two end surfaces of the reactor, bonded with piezoelectric plates, are used as sound radiation surfaces which are 40×40 mm2 and 15×15 mm2, respectively. The calorimetric method is used to measure the acoustic power from the radiation surface into the box with water, and the sodium hyposulphite solution titration method is used to measure the total energy efficiency. An inductor is connected to the sono-reactor in series for increasing the input power of the sono-reactor. Experimental results show that cavitation effect in the sonicated water is the strongest when the driving circuit is in resonance; the total energy efficiency decreases with the increase of input electric power of the sono-reactor; the size of sound radiation surface affects the total energy efficiency, and the efficiency is high when the radiation surface is small.

The acoustic cavitation effect has huge potential applications in a number of industrial fields. Nevertheless, the traditional sono-reactors cannot completely satisfy the industrial processing demands nowadays. One reason for this is the operational cost due to the electric energy consumption. Aiming to overcome the disadvantage, based on a box type sono-reactor (inner size 125.4×40×47 mm3) with one PZT ceramic vibrator and 0.19 L processed solution, the whole system's energy utilization efficiencies at two resonance frequencies, 12.13 kHz and 57.05 kHz, have been investigated. Using calorimetric method and titration, the radiated acoustic energy, total energy efficiency, cavitation efficiency, and electroacoustic efficiency have been measured, respectively. It is found that the more the input volume power is, the less the total energy efficiency would be, both at 12.13 kHz and 57.05 kHz; the total energy efficiency of 12.13 kHz is greater than that of 57.05 kHz, because the micro bubbles caused by the acoustic cavitation absorb acoustic energy. To obtain good energy efficiency and cavitation effect, the input electric power per unit volume should be proper.

A flexible caudal fin made of the macro fiber composites and the carbon fiber orthotropic composite was investigated by the numerical simulations and the experiments. First, a three-dimensional numerical simulation procedure was adopted to research the torsion propulsion mode of the caudal fin and the impact of the water for the structural torsion frequency of the caudal fin. Then, a two-dimensional unsteady fluid computational method was used to analyze the hydrodynamic performance with the periodic swing of the caudal fin on the torsion mode. Based on the simulation results, the flow field was demonstrated and discussed. The interaction between the caudal fin and the water was explained. Finally, the laser vibrometer system was built to verify the torsion propulsion mode. Meanwhile, the application of the caudal fin was realized on the torsion propulsion, and the measured system was established to demonstrate the performance of the caudal fin. The established simulation procedures and experimental methods in this study may provide guidance to the fins made of the composite materials during the structural design and the investigation of the flow field characteristics with the movement of the fins.

Ionic polymer?metal composites (IPMC) are a class of electroactive polymers (EAP), and they currently attract numerous researchers to study their performance characteristics and applications. However, research on its start-up characteristics still requires more attention. In the IPMC start-up state (the moment of applying an actuation voltage at the very beginning), its mechanical performance is different in the stable working state (working for at least 10?min). Therefore, this paper focuses on three performance relationships of an IPMC strip between its maximal tip deformation and voltage, its maximal stress and voltage, as well as its maximal strain and voltage, both in the two states. Different from other reports, we found that they present nonlinear tendencies in the start-up state rather than linear ones. Therefore, based on the equivalent bimorph beam model, a finite element electromechanical coupling calculation module in the ANSYS software was utilized to simulate these characteristics. Furthermore, a test system is introduced to validate the phenomena. As a whole, these three relationships and the FEA method may be beneficial for providing control strategies effectively to IPMC actuators, especially in their start-up states.