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Stabilizing LiCoO2 (LCO) at 4.5 V rather than the common 4.2 V is important for the high specific capacity. In this study, we developed a simple and efficient way to improve the stability of LiCoO2 at high voltages. After a simple sol–gel method, we introduced trifluoroacetic acid (TA) to the surface of LCO via an afterwards calcination. Meanwhile, the TA reacted with residual lithium on the surface of LCO, further leading to the formation of uniform LiF nanoshells. The LiF nanoshells could effectively restrict the interfacial side reaction, hinder the transition metal dissolution and thus achieve a stable cathode–electrolyte interface at high working-voltages. As a result, the LCO@LiF demonstrated a much superior cycling stability with a capacity retention ratio of 83.54% after 100 cycles compared with the bare ones (43.3% for capacity retention), as well as high rate performances. Notably, LiF coating layers endow LCO with excellent high-temperature performances and outstanding full-cell performances. This work provides a simple and effective way to prepare stable LCO materials working at a high voltage. [ABSTRACT FROM AUTHOR]

Identifying grass species in grasslands based on unmanned aerial vehicle hyperspectral remote sensing is the basis and premise of hyperspectral remote sensing when applied to grassland degradation monitoring and research. The small targets and mixed pixels involved grass species identification in grasslands creates problems, making identification cumbersome and classification accuracy difficult. This study involved the construction of an unmanned aerial vehicle hyperspectral remote sensing system using hyperspectral data of grass species in desert habitats that had been collected under natural light. A multi‐resolution combined with a 1 × 1 feature map was formed by multiscale convolution, and grass species data were extracted from hyperspectral fine‐grained feature data from grasslands. A recognition and classification model for degradation indicator species CNN was constructed using max pooling to retain the maximum amount of feature detail and up‐sampling, reconstructing the feature space and feature fusion to smooth the edge texture of the data and enhance the weak data to alleviate the imbalance among samples. The results showed that the overall identification accuracy of the model for grassland species reached 98.78%, and the kappa coefficient reached 0.92, realizing the high‐precision identification of grassland species, which laid the foundation for grassland species detection and research based on unmanned aerial vehicle hyperspectral imagery. In addition, the proposed degradation indicator species CNN model provides a useful reference for the identification and classification of small targets with mixed pixels. [ABSTRACT FROM AUTHOR]

In order to meet the needs of users for large-field of view angle and high resolution of virtual reality head-mounted displays, the initial structure of the optical system was calculated by using reverse design method, and the optical design software was used for simulation analysis optical structure of coaxial large field of view virtual reality head-mounted display. The results show that three aspheric lenses are used in each channel, and the full field angle is 90°, the exit pupil diameter is 8mm, the exit pupil distance is 13mm, the modulation transfer function is greater than 0.3 at Nyquist frequency of 10.581p/mm, and the maximum distortion is 6.1%, respectively. Compared with the reference, the resolution is higher, the distortion is reduced and aberration balance is reasonable. The design provides a reference for optimizing the optical structure of large field of view head-mounted display. [ABSTRACT FROM AUTHOR]

Aiming at the problems of the current head-mounted display with large volume, large weight, and small field of view, in order to meet the user's demand for light and small head-mounted displays, the Ranston eyepiece was used as the initial structure, and then was optimized by using ZEMAX software. Image quality evaluation and tolerance analysis were then carried out. The result shows that each channel in the binocular system uses only two lenses, the maximum field of view of the optical structure is 80°, the total length is 54. 24mm, the maximum distortion is less than 4. 7%, the weight of the two lenses is less than 11. 5 g. Compared with related research, the field angle and the number of pixels are increased, the volume is reduced, and the modulation transfer function is improved. The head-mounted display has certain market prospects, and can provide a reference for the optical design of the light and small head-mounted display. [ABSTRACT FROM AUTHOR]

Picosecond pulse light source is the core device of a quantum key distribution system. In order to realize the localization of picosecond pulse light source, a gigahertz picosecond pulse laser module was developed based on domestic chips. The module was fabricated by using proportion integration division algorithm to control the temperature so that the wavelength drifts within 0.01 nm. The external positive intrinsic negative tube was used to detect the light power, and the driving current of the laser diode was adjusted by feedback. In the meantime, experiments were carried out to verify the theoretical results. The results show that the constant current source and short pulse circuit are controlled accurately by domestic microcontroller to drive the laser diode. The output light pulse frequency can reach 1.25GHz, and the pulse width is about 50ps. When the optical power is - 3dB, the spectral width is less than 0. 2nm, and the output light wavelength and power is stable. The picosecond pulse laser module of localization can meet the requirements of quantum key distribution system for light source stability. [ABSTRACT FROM AUTHOR]