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Debris laser ranging (DLR) is receiving considerable attention as an accurate and effective method of determining and predicting the orbits of space debris. This paper reports some technologies of DLR, such as the high pulse repetition frequency (PRF) laser pulse, large-aperture telescope, telescope array, multi-static stations receiving signals. DLR with a picosecond laser at the Shanghai Astronomical Observatory is also presented. A few hundred laps of space debris laser-ranging measurements have been made. A double-pulse picosecond laser with an average power of 4.2 W, a PRF of 1 kHz, and a wavelength of 532 nm has been implemented successfully in DLR, it's the first time that DLR technology has reached a ranging precision at the sub-decimeter level. In addition, the characteristics of the picosecond-pulse-width laser transmission with the advantages of transmission in laser ranging were analyzed. With a mode of the pulse-burst picosecond laser having high average power, the DLR system has tracked small debris with a radar cross-section (RCS) of 0.91 m2 at a ranging distance up to 1726.8 km, corresponding to an RCS of 0.1 m2 at a distance of 1000 km. These works are expected to provide new technologies to further improve the performance of DLR. [ABSTRACT FROM AUTHOR]

In this study, three japonica rice varieties—Nanjing 9108, Jiahua 1 and Wuyunjing 29—were supplied with different levels of nano-foliar selenium fertilizers (0, 40 and 80 kg Se ha−1) under field conditions. Their rice yield and absorption, accumulation, transportation and utilization of selenium were studied to find suitable selenium-rich rice cultivars and optimal selenium supply levels, while providing references for the development of selenium-rich rice. On an average basis, the Nanjing 9108, Jiahua 1 and Wuyunjing 29 yielded 8755 ± 190, 8200 ± 317 and 9098 ± 72.7 kg ha−1, respectively. The selenium content in polished rice of the three rice varieties is between 0.210 and 0.933 mg kg−1. When 40 g Se ha−1 nano-selenium fertilizer was used, the selenium accumulation in the shoots of Nanjing 9108, Jiahua 1 and Wuyunjing 29 was, respectively, 11.4 g Se ha−1, 12.3 g Se ha−1 and 12.2 g Se ha−1, and when 80 g Se ha−1 selenium fertilizer was applied, the total selenium accumulation of three rice varieties was, respectively, 2.45, 1.75 and 2.40 times that of 40 g Se ha−1 selenium fertilizer. No evident diversity was observed in the selenium transport coefficient and the apparent utilization rate of selenium among the three varieties. The three rice varieties in this experiment had a strong selenium enrichment capacity, and they could be planted as selenium-enriched and high-yield rice varieties. Further, the amount of selenium fertilizer should not exceed 40 g Se ha−1. [ABSTRACT FROM AUTHOR]

Nonwoven fiber materials are materials with multifunctional purposes, and are widely used to make masks for preventing the new Coronavirus Disease 2019. Because of the complexity and particularity of their structure, it becomes difficult to model the penetration and flow characteristics of liquid in nonwoven fiber materials. In this paper, a novel seepage time soft sensor model of nonwoven fabric, based on Monte Carlo (MC), integrating extreme learning machine (ELM) (MCELM) is proposed. The Monte Carlo method is used to expand data samples. Then, an ELM method is used to establish the prediction model of the dyeing time of the nonwoven fiber material overlaps with the porous medium, as well as the insertion degree and height of the different quantity of hides. Compared with the back propagation (BP) neural network and radial basis function (RBF) neural network, the results show that the prediction model based on the MCELM method has significant power in terms of accuracy and prediction speed, which is conducive to the precise and rapid manufacture of nonwoven fiber materials in practical applications between liquid seepage characteristics and structural characteristics of porous media. Furthermore, the relationship between the proposed models has certain value for predicting the behavior and use of nonwoven fiber materials with different structural characteristics and related research processes. [ABSTRACT FROM AUTHOR]

Laser time transfer is of great significance in timing and global time synchronization. However, the temperature drift may occur and affect the delay of the electronics system, optic generation and detection system. This paper proposes a post-processing method for the compensation of temperature-induced system delay, which does not require any changes to the hardware setup. The temperature drift and time stability of the whole system are compared with and without compensation. The results show that the propagation delay drift as high as 240 ps caused by temperature changes is compensated. The temperature drift coefficient was diminished down to ~0.05 ps/°C from ~20.0 ps/°C. The system precision was promoted to ~2 ps from ~11 ps over a time period of 80,000 s. This method performs significant compensation of single-photon laser time transfer system propagation drift and will help to establish an ultra-stable laser time transfer link in space applications. [ABSTRACT FROM AUTHOR]

A critical requirement to achieve high efficiency of debris laser tracking is to have sufficiently accurate orbit predictions (OP) in both the pointing direction (better than 20 arc seconds) and distance from the tracking station to the debris objects, with the former more important than the latter because of the narrow laser beam. When the two line element (TLE) is used to provide the orbit predictions, the resultant pointing errors are usually on the order of tens to hundreds of arc seconds. In practice, therefore, angular observations of debris objects are first collected using an optical tracking sensor, and then used to guide the laser beam pointing to the objects. The manual guidance may cause interrupts to the laser tracking, and consequently loss of valuable laser tracking data. This paper presents a real-time orbit determination (OD) and prediction method to realize smooth and efficient debris laser tracking. The method uses TLE-computed positions and angles over a short-arc of less than 2 min as observations in an OD process where simplified force models are considered. After the OD convergence, the OP is performed from the last observation epoch to the end of the tracking pass. Simulation and real tracking data processing results show that the pointing prediction errors are usually less than 10″, and the distance errors less than 100 m, therefore, the prediction accuracy is sufficient for the blind laser tracking.