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In machining processes, chatter vibrations are always regarded as one of the major limitations for production quality and efficiency. Accurate and timely monitoring of chatter is helpful to maintain stable machining operations. At present, most chatter monitoring methods are based on the energy level at specified chatter frequencies or frequency bands. However, the spectral features of chatter could change during machining operations due to complexity and time-varying dynamics of the physical machining process. The purpose of this paper is to investigate the time-varying chatter features in turning of thin-walled tubular workpieces from the perspective of entropy. The airborne acoustics was selected as the source of information for machining condition monitoring. First, corresponding to the distinguishing surface topographies relevant to machining conditions, the features of the sound signal emitted during turning of the thin-walled cylindrical workpieces were extracted using the spectral analysis and wavelet packet transform, respectively. It was shown that the dominant vibration frequency as well as the energy distribution could shift with the transition of the machining status. After that, two relative entropy indicators based on the spectrum and the wavelet packet energy were constructed to identify chattering events in turning of the thin-walled tubes. The experimental results demonstrate that the proposed indicators could accurately reflect the transition of machining conditions with high sensitivity and robustness in comparison with the traditional FFT-based methods. The achievement of this study lays the foundations of the online chatter monitoring and control technique for turning of the thin-walled tubular workpieces.

Rural domestic waste classification (RDWC) is one of the main strategies for waste management, which plays a significant role in the circular economy and sustainable management. As one of the first pilot cities of waste classification in China, Hangzhou took the lead in promoting the classification and recycling of rural domestic waste. Based on the probability sampling procedure, this study focuses on the influencing factors of residents’ awareness and behaviors toward RDWC in Hangzhou rural areas. The results of the questionnaire survey show that the perception of the importance of RDWC is weak in rural areas of China. Moreover, regression analyses show that the public’s RDWC awareness is positively influenced by the cleanliness of waste rooms, age, and educational level. And their RDWC behaviors are negatively influenced by human supervision but positively influenced by the attitude to waste classification, satisfaction with the situation of RDWC and environment. Besides, exploring the relationship between the number of COVID-19 cases and the waste classification performance shows cities with better waste classification performance have fewer confirmed cases. These results imply that the proper waste classification methods and supporting infrastructure facilities could be fitted to other rural areas. © 2021, HARD Publishing Company. All rights reserved.

With the goal of solving the problems of difficult data acquisition and low prediction accuracy in the reliability analysis of shearer rocker arms, this paper proposes a remaining useful life (RUL) prediction method for bearings of shearer rocker transmission parts based on Internet of Things (IoT). In the perception layer, data acquisition from shearer equipment at a fully mechanized mining face is consisting of a broadband wireless network and a narrowband wireless network. For the data analysis layer, a window autoencoder (WAE)-long short-term memory (LSTM)-based RUL prediction method is proposed. An WAE is constructed based on the self-supervised learning characteristics of autoencoders (AEs) to extract the features of the data, and a prediction model is established based on the time-series characteristics of LSTM networks. The advantages of the proposed method are that it can eliminate the dependence on a large number of signal processing techniques and diagnostic experience, enable the adaptive extraction of features and intelligent RUL prediction. Experimental results show that the proposed method can accurately predict the bearings RUL of a shearer rocker transmission part.

In this letter, TiO2 thin films were prepared via sol-gel method and metal/semiconductor/metal ultraviolet (UV) detectors with Pt Schottky contact were fabricated. At 5 V bias, the dark current of the device was only 80 pA. Diffusion theory was adopted to analyze the low dark current mechanism, which is consistent with the experimental results. The device shows a remarkably reduced decay time of 41.53 ms. The low dark current and improved time response performance may be attributed to the high effective Schottky barrier between Pt and TiO2 film. High responsivity of 34.5 A/W was achieved at 300 nm UV light and the ratio of photocurrent to dark current is about five orders of magnitude, which is much larger than that of other semiconductor photodetectors.

In this letter, metal–semiconductor–metal (MSM) ultraviolet TiO 2 photodetectors based on LaAlO 3 substrate were fabricated. TiO 2 nano-film was prepared via a sol–gel method, and then was spin-coated on single crystal LaAlO 3 substrate. Pt interdigitated electrodes were deposited on the top of TiO 2 film. At 5 V bias, the dark current of the detector was only 50 pA, which is much lower than TiO 2 -based detector. When irradiated by 270 nm UV light, a high photoresponse of the device was obtained. The ratio of photocurrent to dark current was nearly 5 orders, which is much higher than other photodetectors based on TiO 2 reported. The rise and fall time of the detector were 550 ms and 380 ms, respectively. The very low dark current and high sensitivity demonstrate the excellent application of the device in UV photoelectric detection.

In this letter, a nanocrystalline SrZr0.1Ti0.9 O3thin film was synthesized by sol-gel method and characterized by means of X-ray diffraction, X-ray photoelectron spectroscopy, atomic force microscopy, and UV-visible absorption spectra. Interdigitated Au electrodes were deposited on the film to fabricate metal-semiconductor-metal ultraviolet photodetector. At 5-V bias, the dark current of the device was 41 pA. Under the irradiation of 260-nm UV light, peak responsivity of 94 mA/W was achieved, which was higher than that of pure SrTiO3-based photodetectors. The higher responsivity of the SrZr0.1Ti0.9O3 device may be due to the introduction of zirconia, which would induce more oxygen vacancies. The UV/visible rejection ratio R260 nm/R380 nm was more than three orders of magnitude, indicating excellent sensitivity. The rise time and fall time of the device were 3.8 and 565 ms, respectively.

In this letter, a Schottky diode ultraviolet (UV) detector based on TiO2 nanowire (NW) array with Ag electrode is fabricated. The TiO2 NW array was prepared via a low-temperature hydrothermal method and characterized by means of X-ray diffraction, scanning electron microscope, and XPS. The Schottky barrier character of Ag/TiO2 contact was researched in detail. At -5-V bias, the dark current of the detector was less than 35 nA. Under the irradiation of 350-nm UV light, a high responsivity of 3.1 A/W was achieved due to the internal gain. The Schottky diode detector with simple fabrication process, low cost, and superior performance would provide a new way in fabricating UV imaging arrays.

In this letter, TiO₂ nanocrystalline film was prepared on SrTiO₃ (001) substrate to form an n-n heterojunction active layer. Interdigitated Au electrodes were deposited on the top of TiO₂ film to fabricate modified HMSM (heterojunction metal-semiconductor-metal) ultraviolet photodetector. At 10 V bias, the dark current of the detector was only 0.2 nA and the responsivity was 46.1 A/W at 260 nm. The rise and fall times of the device were 3.5 ms and 1.4 s, respectively. The TiO₂/SrTiO₃ heterojunction contributed a lot to the high responsivity and reduced the fall time, which improved the device performance effectively. These results demonstrate the excellent application of TiO₂/SrTiO₃ heterojunction in fabricating high performance UV photodetectors.

In this letter, TiO2 nanocrystalline film was prepared on SrTiO3 (001) substrate to form an n-n heterojunction active layer. Interdigitated Au electrodes were deposited on the top of TiO2 film to fabricate modified HMSM (heterojunction metal-semiconductor-metal) ultraviolet photodetector. At 10 V bias, the dark current of the detector was only 0.2 nA and the responsivity was 46.1 A/W at 260 nm. The rise and fall times of the device were 3.5 ms and 1.4 s, respectively. The TiO2/SrTiO3 heterojunction contributed a lot to the high responsivity and reduced the fall time, which improved the device performance effectively. These results demonstrate the excellent application of TiO2/SrTiO3 heterojunction in fabricating high performance UV photodetectors.