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Location-based services are now playing an integral role in the development of emerging industries, such as the Internet of Things, artificial intelligence and smart cities. Although GPS, Beidou and other satellite positioning technologies are becoming more and more mature, they still have certain limitations. In order to meet the needs of high-precision positioning, wireless positioning is proposed as a supplementary technology to satellite positioning, in which the Received Signal Strength Indication (RSSI) is one of the most popular positioning methods. In this paper, the application scenarios, evaluation methods and related localization methods of wireless positioning based on RSSI are studied. Secondly, the relevant optimization methods are analyzed and compared from different angles, and the methods of RSSI data acquisition are described. Finally, the existing problems and future development trends in RSSI positioning methods are expounded, which has certain reference significance for further research on RSSI localization. [ABSTRACT FROM AUTHOR]

Fulvic acid (FA), the essence and most active component in humus, is widely used as a fertilizer synergistic agent and for soil improvement. As a synergist, FA can not only highly chelate microelements, but also play a key role as a growth promoter. Due to the small molecular weight and high solubility, FA is usually used by foliar spraying in vegetable production, yet the effect on fruit quality and nutrient absorption is still unclear. Here, 'Jinpengdashuai' tomatoes were used to investigate the effects of spraying FA on tomato fruit quality and soil Cu and Cd availability under stress of Cu and Cd by pot experiments. The results showed that the 1000 mg·L−1 FA could significantly improve the biomass of tomato plants to some extents under different stresses of Cu and Cd. After spraying FA, the Cu and Cd content in different organs and the whole accumulation decreased; meanwhile, the transport efficiency of Cu and Cd was also reduced to some degree. The drops of FA significantly changed the chemical form of Cu and Cd in 0~10 cm soil, from the easily absorbed water soluble (or ion) form into the insoluble form, hard to absorb. The Cu content in the residual state increased by 93.8% and 172.5%, respectively, under single and compound stress, and the Cd content in the residual state increased by 16.7% and 58.6%. Foliar spraying FA could promote the absorption and transport of essential nutrients such as nitrogen, phosphorus, potassium, calcium, magnesium and zinc, and maintain the nutrient balance, which alleviates the inhibition of normal metabolism by Cu and Cd stress, to a certain extent. More distinctly, Vc, total sugar and lycopene increased by 11.4~45.9%, 19.2~48.5% and 30.9~84.5%, respectively, indicating that foliar spraying FA could improve the appearance and flavor quality of tomato fruits under stress of Cu and Cd. [ABSTRACT FROM AUTHOR]

The aim was to improve the fertilizer utilization efficiency and alleviate environmental pollution risk under a wheat-maize rotation system. Here, the combinations of different nitrogen stabilizers and phosphorus activators were used to reduce nitrogen loss and phosphorus fixation in the field experiment. Compared to the control, the combination of 1.5%HQ + 0.5%DMPP + biochar showed the most significant effect on the retention of alkali-hydrolysable nitrogen (Nah), the highest with an increase of 22.6% at the 0~20 cm layer soil; and the combination of 1.5%HQ + 3.5%DCD + CMFs (compound microbial fertilizers) showed the most significant effect on the maintenance of available phosphorus (Pa), with the highest increase of 41.3%. N, P synergists combined with a basal fertilizer could effectively slow down the transformation from N H 4 + to N O 3 − , and keep N H 4 + at an increase of 7.38%~19.6%. Moreover, the N, P synergists could efficiently lock the available nutrients around the roots, preventing the migration of N O 3 − , N H 4 + , Nah, and Pa to the deeper layers. Especially for N O 3 − , the total accumulation at 0~60 cm decreased by 32.1%, and the activation of Pa was mainly concentrated at 0~40 cm. Under the same nutrient inputs, the combination of 0.3%NBPT + 0.5%DMPP + CMFs obtained the highest wheat yield. The combination of 1.5%HQ + 0.5%DMPP+ biochar gained the highest maize yield. Overall, the application of N, P synergists could increase the effective duration of Nah, Pa, and N H 4 + in the surface soil, and reduce the accumulation of N O 3 − in the 0~60 cm soil layer. The capacity of holding and keeping nutrients from leaching rose obviously; simultaneously, the assimilative capacity of crops for nitrogen and phosphorus increased distinctly, which could lower the eutrophia risks from nitrogen and phosphorus. [ABSTRACT FROM AUTHOR]

The reasonable placement of evacuation signage is an important means to improve the efficiency of evacuation in the exhibition halls of exhibition buildings. The booths in exhibition halls are arranged and changed frequently for different exhibitions, which means that the evacuation paths are not fixed. Most people are also unfamiliar with the exhibition hall environment. In case of fire, earthquake, or other emergencies, people need to quickly escape to the safety exit, adhering to the guidance of evacuation signage. Existing evacuation signs are located according to the standards and the experience of the designers, and the locations of the signs are fixed and do not change with the changes in the booth layout, which means that the signage can be easily obscured by the booths, affecting the signage identification. Based on the visibility of evacuation signage, a smart design method of evacuation signage layout is proposed in this paper that can be adapted to different forms of booth arrangements in exhibition halls. This method establishes a key goal of achieving the full coverage of the visibility range of evacuation passages with the minimum number of evacuation signs. In the context of the actual visibility range of evacuation signage being blocked by booths in a three-dimensional space, this method finds the optimal number and best locations of evacuation signs by using a genetic algorithm. Finally, a case is given to verify the effectiveness of the method. This smart design for evacuation signage layout can enhance the guidance ability of evacuation signage in exhibition halls and improve the efficiency of evacuation. [ABSTRACT FROM AUTHOR]

The ring-opening polymerization of δ-valerolactone catalyzed by a thermophilic esterase from the archaeon Archaeoglobus fulgidus was successfully conducted in organic solvents. The effects of enzyme concentration, temperature, reaction time and reaction medium on monomer conversion and product molecular weight were systematically evaluated. Through the optimization of reaction conditions, poly(δ-valerolactone) was produced in 97% monomer conversion, with a number-average molecular weight of 2225 g/mol, in toluene at 70 °C for 72 h. This paper has produced a new biocatalyst for the synthesis of poly(δ-valerolactone), and also deeper insight has been gained into the mechanism of thermophilic esterase-catalyzed ring-opening polymerization.