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This paper proposes an improved TD3 (Twin Delayed Deep Deterministic Policy Gradient) algorithm to address the flaws of low success rate and slow training speed, when using the original TD3 algorithm in mobile robot path planning in dynamic environment. Firstly, prioritized experience replay and transfer learning are introduced to enhance the learning efficiency, where the probability of beneficial experiences being sampled in the experience pool is increased, and the pre-trained model is applied in an obstacle-free environment as the initial model for training in a dynamic environment. Secondly, dynamic delay update strategy is devised and OU noise is added to improve the success rate of path planning, where the probability of missing high-quality value estimate is reduced through changing the delay update interval dynamically, and the correlated exploration of the mobile robot inertial navigation system in the dynamic environment is temporally improved. The algorithm is tested by simulation where the Turtlebot3 robot model as a training object, the ROS melodic operating system and Gazebo simulation software as an experimental environment. Meanwhile, the result shows that the improved TD3 algorithm has a 16.6 % increase in success rate and a 23.5 % reduction in algorithm training time. A generalization experiment was designed finally, and it indicates that superior generation performance has been acquired in mobile robot path planning with continuous action spaces through the improved TD3 algorithm.

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Single-atom alloys (SAAs) have gained increasing prominence in the field of selective hydrogenation reactions due to their uniform distribution of active sites and the unique host-guest metal interactions. Herein, 15 SAAs are constructed to comprehensively elucidate the relationship between host-guest metal interaction and catalytic performance in the selective hydrogenation of 4-nitrostyrene (4-NS) by density functional theory (DFT) calculations. The results demonstrate that the SAAs with strong host-guest metal interactions exhibit a preference for N─O bond cleavage, and the reaction energy barrier of the hydrogenation process is primarily influenced by the host metal. Among them, Ir1Ni SAA stands out as the prime catalyst candidate, showcasing exceptional activity and selectivity. Furthermore, the Ir1Ni SAA is subsequently prepared through precise synthesis techniques and evaluated in the selective hydrogenation of 4-NS to 4-aminostyrene (4-AS). As anticipated, the Ir1Ni SAA demonstrates extraordinary catalytic performance (yield > 96%). In situ FT-IR experiments and DFT calculations further confirmed that the unique host-guest metal interaction at the Ir-Ni interface site of Ir1Ni SAA endows it with excellent 4-NS selective hydrogenation ability. This work provides valuable insights into enhancing the performance of SAAs catalysts in selective hydrogenation reactions by modulating the host-guest metal interactions.

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The hydroalkylation tandem reaction of benzene to cyclohexylbenzene (CHB) provides an atom economy route for conversion and utilization of benzene; yet, it presents significant challenges in activity and selectivity control. In this work, we report a metal-support synergistic catalyst prepared via calcination of W-precursor-containing montmorillonite (MMT) followed by Pd loading (denoted as Pd-mWOx/MMT, m = 5, 15, and 25 wt %), which shows excellent catalytic performance for hydroalkylation of benzene. A combination study (X-ray diffraction (XRD), hydrogen-temperature programmed reduction (H2-TPR), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV-vis, Raman, and density functional theory (DFT) calculations) confirms the formation of interfacial sites Pd-(WOx)-H, whose concentration is dependent on the interaction between Pd and WOx. The optimized catalyst (Pd-15WOx/MMT) exhibits a CHB yield of up to 45.1% under a relatively low hydrogen pressure, which stands at the highest level among state-of-the-art catalysts. Investigations on the structure-property correlation based on in situ FT-IR and control experiments further verify that the Pd-(WOx)-H structure serves as the dual-active site: the interfacial Pd site accelerates benzene hydrogenation to cyclohexene (CHE), while the interfacial Bronsted (B) acid site in Pd-(WOx)-H boosts the alkylation of benzene and CHE to CHB. This study offers a new strategy for the design and preparation of metal-acid bifunctional catalysts, which shows potential application in the hydroalkylation reaction of benzene.

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A method had been developed for the determination of three N-nitrosamines, namely, N-nitrosodimethylamine (NDMA), N-nitrosomethylethylamine (NMEA), and N-nitrosodiethylamine (NDEA) in drinking water by solid phase extraction (SPE) and gas chromatography-triple quadrupole mass spectrometry (GC-QqQ-MS/MS) with programmable temperature vaporizer (PTV)-based large volume injection (LVI). The N-nitrosamine compounds were extracted from the water sample using a solid phase extraction (SPE) cartridge filled with coconut charcoal, and then eluted with 10 mL methylene chloride. The eluate was dried by anhydrous sodium sulfate and 10 µL was injected into the GC-MS/MS by PTV-LVI. The target compounds were detected by the multi-reaction monitoring (MRM) mode, and quantified with the external standard method. The results showed that the three compounds had good linearities in the range of 1-50 ng/L with correlation coefficients (r2) higher than 0.999. Drinking water samples were spiked with the target compounds at three concentration levels (10, 20, and 50 ng/L), and satisfactory recoveries (between 94.8% and 109%) and good reproductivities (relative standard deviation RSD<10%) were achieved. The limits of quantitation (LOQs) of the three N-nitrosamines were found to be in the range of 0.08-0.7 ng/L. The developed method was sensitive, accurate, convenient, and reliable for the determination of the three trace level N-nitrosamines in drinking water.

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OBJECTIVE: To establish a method for determining o-tolidine in workplace air by gas chromatography. METHODS: o-tolidine in workplace air was collected with a glass fiber filter, desorbed with methanol, and determined by gas chromatography-flame ionization detector. RESULTS: The concentration of o-tolidine showed a linear relationship with peak area within 0.04∼9.00 µg/ml; the detection limit was 0.04 µg/ml; the minimum detectable concentration was 0.0002 mg/m(3) (calculated by 375 L air sample); the sampling efficiency was 93%∼100%; the elution efficiency was 94%∼96%; the relative standard deviation was 0.8-2.5%. Sample could be stored at 4 °C for at least 8 days and at room temperature for as long as 6 days. CONCLUSION: This determination method meets the requirements of Guide for establishing occupational heath standards-Part 4 Determination methods of air chemicals in workplace (GBZ/T 210.4-2008) and is suitable for determination of o-tolidine in workplace air.

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