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Code Differential Global Positioning System (DGPS) is widely used in satellite navigation and positioning because of its simple algorithm and preferable precision. Multi-Global Navigation Satellite System (GNSS) is expected to enhance the accuracy, reliability and availability of Differential GNSS (DGNSS) positioning. Traditional DGNSS models should set separate clock parameters due to the clock differences between the different systems. Awareness of the Inter-System Bias (ISB) could help to maximise the redundancy of the positioning model, thus improving the performance of multi-GNSS positioning. This paper aims to examine the inter-system bias of GPS/GLONASS/BeiDou (BDS)/Galileo and their benefits in DGNSS positioning. Results show that Differential ISB (DISB) characteristics vary with different receiver types and systems. The size of DISB could reach metre-level and the precision of estimated DISBs can reach approximately several centimetres within tens of epochs. Therefore, a new real-time DGNSS model that accounts for ISB is proposed. After differential ISBs are initialised, positioning with four satellites from arbitrarily the same or different systems can be realised. Moreover, compared with the traditional DGNSS model, the precision of the positioning results with the new model are obviously improved, especially in harsh environments.

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In order to clarify the effect of sodium on the heterogeneous adsorption of NO on a char surface, several reasonably simplified saturated and unsaturated char models were selected as research objects, and Na atoms were decorated on the char models. Each char model and NO adsorption product were optimized by using density functional theory at the GGA-PBE (generalized gradient approximation-Perdew−Burke−Ernzerhof) level to obtain the adsorption energy of NO on different models. The results indicate that the addition of Na atoms catalyzes the adsorption of NO molecules by an saturated char structure, the adsorption form is changed from physisorption to chemisorption, and the adsorption energy is increased from −15.6 to −98.2 kJ/ mol. The adsorption energy of NO molecules with an unsaturated armchair-type char structure containing edge active sites is affected by sodium atoms, increasing from −211.7 to −303.6 kJ/mol, while the adsorption capacity of the zigzag-type char structure for NO molecules is hardly affected by Na atoms. This study provides a theoretical basis for the development of clean utilization technology of high-alkali coal.

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Sodium in high-alkali coal facilitates the heterogeneous reduction of nitrogen oxides on char surfaces. However, the reaction mechanism is unclear. In this paper, the effect of sodium on the reaction path of the char heterogeneous reduction of NO was analyzed based on the first-principles study using an armchair char model and a zigzag char model separately. Four reaction paths were obtained, and the most likely reaction path was found by comparison. The highest energy barriers of the reduction reactions were reduced to some extent by doping with the sodium atom. The doped sodium atom had a significant effect on the heterogeneous reduction reactions on the surface of the armchair char and had little effect on the surface of the zigzag char. However, a comprehensive analysis showed that the reactivity of the zigzag model is better than that of the armchair model. From the thermodynamic analysis, the addition of the sodium atom could change the reaction from nonspontaneous to spontaneous. After the completion of the reaction, the oxygen atom would be immobilized on the char structure surface, which will have an effect on the subsequent reaction. This study revealed the effect of the sodium atom on the reaction mechanism of the char heterogeneous reduction of NO and helped perfect the mechanism of the char heterogeneous reduction of NO.

Objective: To evaluate the impact of the first round of the National Centralized Drug Procurement (NCDP) pilot (referred to as "4+7" policy) on the use of policy-related original and generic drugs. Methods: Drug purchase data from the China Drug Supply Information Platform (CDSIP) database were used, involving nine "4+7" pilot cities and 12 non-pilot provinces in China. "4+7" policy-related drugs were included, which consisted of 25 "4+7" List drugs and 97 alternative drugs that have an alternative relationship with "4+7" List drugs in clinical use. "4+7" List drugs were divided into bid-winning and non-winning products according to the bidding results. Purchase volume, purchase expenditures, daily costs were selected as outcome variables, and were measured using Defined Daily Doses (DDDs), Chinese Yuan (CNY), and Defined Daily Drug cost (DDDc), respectively. Difference-in-Difference (DID) method was employed to estimate the net effect of policy impact. Results: After policy intervention, the DDDs of original drugs among "4+7" List drugs significantly reduced by 124.59%, while generic drugs increased by 52.12% (all p-values <0.01). 17.08% of the original drugs in DDDs were substituted by generic drugs. Prominent reductions of 121.69% and 80.54% were observed in the expenditure of original and generic drugs, with a total cost-saving of 5036.78 million CNY for "4+7" List drugs. The DDDc of bid-winning original and generic drugs, as well as non-winning original drugs, significantly decreased by 33.20%, 75.74%, and 5.35% (all p-values <0.01), while the DDDc of non-winning generic drugs significantly increased by 73.66% (p<0.001). The use proportion of bid-winning products and non-winning original drugs raised prominently from 39.66% to 91.93% Conclusions: "4+7" policy promoted the substitution use of generic drugs against original drugs, which conducive to drug costs saving. The overall quality level of drug use of public medical institutions significantly increased after "4+7" policy, especially in primary medical institutions.