Search

The polarization switching properties of P(VDF-TrFE) ultrathin films with different storage periods were measured. The dependence of polarization properties on temperature and storage period was investigated. The experimental results suggest that the relative remanent polarization (Pr/Pr0) remains on a relatively high level of 0.70 at 60℃, 106 polarzation swiching test, even to the ultrathin film capacitors stored in atmosphere for five months. The time stability model of polarization switching is predicted by the evolution of polarization switching with the number of electric field cycles. Moreover, when the changes of the molecular chain are simulated by different storage periods and testing temperatures, an inhibited hydrogen fluoride (HF) gas formation scheme in the capacitors was proposed. This work further validated the time stability model and microscopic dynamics associated with trapped charge. These results provide an effective method for designing an optimum protocol for flexible electronic devices based on P(VDF-TrFE) copolymer ultrathin films.

Bismuth layer structured piezoelectric ceramics, Na0.5Bi4.5TaxTi4-xO15+0.5x (NBT-Ta-x)(x=0-0.20), were fabricated via a solid state sintering process. The effect of Ta5+ doping for B site on the microstructure, electrical conductivity,dielectric and piezoelectric properties of NBT-Ta-x ceramics was investigated by means of XRD, SEM and an automatic temperature control testing system. The results show that Ta doping brings about the decrease in grain size and aspect ratio of grain with a preferable orientation growth along c-axis. Meanwhile, both theoretical density and measured density of the ceramics is increased with increasing tantalum doping content, with the highest relative density of 96.1% at x=0.05, showing that the solid solution limit of tantalum in NBT lattice is in the proximity of x=0.10. The Curie temperature is decreased slightly from 680℃ to 658℃ with the increase of Ta5+ doping content x to 0.20. The electrical resistivity of NBT-Ta-x ceramics is increased as much as about two orders of magnitude by Ta5+ modification and the piezoelectric constant d33 values is increased significantly from 13.8 pC/N to 23 pC/N. The x=0.04-0.05 samples exhibit the optimal electrical performance:Tc=670-672℃,d33=21.8-23 pC/N, kp=7.9%-8.3%.

A mathematical model to describe the seismic vibrator and ground coupling is proposed based on dynamic analyses of the vibrator baseplate structure and properties of soil. This mathematical model is solved using Newmark’s method. It produces reasonable results and the trend of amplitude envelope follows the experimental data. With this model, characterization of the vibrator-ground coupling is performed. Modal analysis study shows that the motions between the vibrator reaction mass and baseplate experience a combination of a first-order vibration mode and a second-order vibration mode. The corresponding frequencies of two vibration modes are located at 2.77 Hz and 488.7 Hz, respectively. As the frequency goes up, the motion behavior of the reaction mass and baseplate is dominated by the second-order vibration mode. It is realized that the second-order vibration mode is responsible for the phase difference between the input sweep signal and the output force signal. Furthermore, the impact of the coupling system parameters on the vibrator output force is also investigated. It is observed that the vibrator output force decreases as the sweep frequency increases. The weight ratio of the reaction mass and the baseplate has an impact on the vibrator output force.

Due to the huge amount of parameters of the YOLOv4 neural network with CSPDarknet53 as the backbone, the detection accuracy and speed will be reduced when it is transplanted to small devices such as mobile phones. In order to improve the detection speed and control the detection accuracy within a reasonable range, this paper proposes to change the original 53-layer neural network to a 15-layer one, and optimizes its clustering algorithm. The K-means++ clustering algorithm is introduced to analyze the data set to generate an anchor box that satisfies the detection conditions. LeakyReLU activation function with a certain slope in the negative interval is used to replace the Sigmoid activation function with vanishing gradients, thereby enhancing the learning ability of the shallow network. At the same time, considering that the center distance and the aspect ratio between the Bounding Box and the Anchor Box have a certain correlation, The corresponding penalty term is added to the original loss function to generate the LCIoU loss function, so that the loss function has a better directionality of the gradient drop during back propagation. Experimental results show that the improved CSPDarknet15 neural network in the VOC2007 data set has an average detection accuracy of 83.94%, and the detection time of a picture is 3 625 ms. Compared with the CSPDarknet53 neural network, the detection speed is increased by 54.43%, which can meet the speed and accuracy requirements of real-time detection of small devices. [ABSTRACT FROM AUTHOR]

It is still hotly debated whether the subduction of the Indus-Yarlung Zangbo Tethyan oceanic lithosphere led to Cretaceous magmatism in the north Lhasa terrane or not. Here, we provide new data on adakitic dacite in the Rutog area, western Tibetan Plateau. Zircon U-Pb dating and Lu-Hf analyses yielded a weighted-mean 206Pb/238U age of ca. 97 Ma for a dacite sample, and corresponding positive zircon εHf(t) values of +5.3 to +10.1. All samples have high Sr (796–1091ppm), but low Y (10.4–11.9 ppm) and Yb (0.68–0.79 ppm) contents, with pronounced high Sr/Y (72.5–97.6) ratios. Furthermore, they have low K2O (1.11–1.49 wt.%) and Th (4.18–4.54 ppm) contents, and low K2O/Na2O (0.18–0.28) and Th/La (0.22–0.24) ratios. These geochemical features are most simialr to those of adakite derived from partial melting of subducted oceanic slab. These new data, in combination with regional geology, enable us to suggest that the Late Cretaceous arc-affinity magmatic rocks were probably triggered by northward subduction of the Indus-Yarlung Zangbo oceanic lithosphere. This will give new insights into the geodynamic evolution of the Indus-Yarlung Zangbo Neo-Tethys Ocean. [ABSTRACT FROM AUTHOR]