[Precipitation variation reconstructed based on tree-ring width data for the past 399 years in the eastern Yinshan Mountains, China]. / åŸºäºŽæ ‘è½®å®½åº¦æ•°æ®é‡å»ºçš„é˜´å±±ä¸œéƒ¨è¿‡åŽ»399年降水变化.

Based on the tree-ring increment cores of Pinus tabuliformis collected from the eastern Yinshan Mountains, the tree-ring width chronology was developed. The correlation coefficients were calculated between the chronology and monthly mean temperature and monthly precipitation during the instrumental period of AD 1952-2007. The results showed that the highest correlation was found between the total precipitation from September of previous year to June of current year and the chronology (r=0.73, n=56, P<0.01). Based on the correlation, the September of previous year to June of current year total precipitation variation was reconstructed in the eastern Yin-shan Mountains during the past 399 years (AD 1619-2017). The reconstruction explained 54.9% of the variation in the total precipitation from September of previous year to June of current year for the calibration period (AD 1952-2007). Both the 'leave-one-out' cross validation and split-period validation showed that the model was relatively robust, with sufficient skills of estimation and high reliability. At the decadal scale, there were four wet periods (AD 1619-1663, AD 1705-1711, AD 1945-1963, and AD 1979-2017)) and four dry periods (AD 1734-1767, AD 1786-1814, AD 1839-1867, and AD 1888-1942) in the past 399 years. Among those periods, the AD 1979-2017 was the wettest period, and AD 1888-1942 was the longest dry duration with the driest period at the late 1920s. Results of power spectral analysis revealed cyclic fluctuations of precipitation series on 2-7 years and 125 years. In addition, the comparison with other reconstructions and spatial correlation analysis indicated that the reconstructed precipitation series well represented regional scale precipitation variation.

[Influence of large volcanic eruptions on climate as revealed by tree-ring data on the Tibetan Plateau, China]. / æ ‘è½®æ•°æ®æ­ç¤ºçš„å¼ºç«å±±å–·å‘å¯¹é’è—é«˜åŽŸåœ°åŒºæ°”å€™çš„å½±å“.

Large volcanic eruption is an important factor affecting global climate change. In the past few decades, many researchers reconstructed a number of climate series based on tree rings on the Tibetan Plateau, and examined the impacts of large volcanic eruptions on the climate. The results showed that these tree-ring sites used to examined the influences of large volcanic eruptions on climate change were primarily located in the eastern Tibetan Plateau. In addition, the series comparison and the superposed epoch analysis were main methods for studying the climate effects of large volcanic eruptions. Based on the results analyzed using two methods, we suggested that the large volcanic eruptions in low-mid latitudes had a significant impact on temperature and dry/wet variation. Cooling or drought occurred after large volcanic eruptions in the subsequent 1-2 years. How-ever, the large volcanic eruptions in high latitudes had minor impacts on climate change. Furthermore, consecutive multiple volcanic eruptions could result in cooling at the decades scale. The factors influencing the climate effects of large volcanic eruptions included the location of the volcanic eruptions, intensity of the volcanic eruptions, atmospheric circulation, etc. Finally, we proposed research projects that need to be carried out in the future.

A new air-stable Si,S-chelating ligand for Ir-catalyzed directed ortho C-H borylation.

A new air-stable Si,S-chelating ligand has been developed and used in an iridium-catalyzed ortho C-H borylation reaction with a broad substrate scope. This study provides the first example of using a sulfur-containing ligand in the catalytic C-H borylation process. It provides a rapid, efficient, and economical method for the preparation of organoboron compounds.

Multi-Step Continuous-Flow Organic Synthesis: Opportunities and Challenges.

Continuous-flow multi-step synthesis takes the advantages of microchannel flow chemistry and may transform the conventional multi-step organic synthesis by using integrated synthetic systems. To realize the goal, however, innovative chemical methods and techniques are urgently required to meet the significant remaining challenges. In the past few years, by using green reactions, telescoped chemical design, and/or novel in-line separation techniques, major and rapid advancement has been made in this direction. This minireview summarizes the most recent reports (2017-2020) on continuous-flow synthesis of functional molecules. Notably, several complex active pharmaceutical ingredients (APIs) have been prepared by the continuous-flow approach. Key technologies to the successes and remaining challenges are discussed. These results exemplified the feasibility of using modern continuous-flow chemistry for complex synthetic targets, and bode well for the future development of integrated, automated artificial synthetic systems.

Recent Progress in Continuous-Flow Hydrogenation.

To achieve a safe, efficient, and sustainable (even fully automated) production for the continuous-flow hydrogenation reactions, which is among the most often used reactions in chemical synthesis, new catalyst types and immobilization methods as well as flow reactors and technologies have been developed over the last years; in addition, these approaches have been combined with new and transformational technologies in other fields such as artificial intelligence. Thus, attention from academic and industry practitioners has increasingly focused on improving the performance of hydrogenation in flow mode by reducing the reaction times, increasing selectivities, and achieve safe operation. This Minireview aims to summarize the most recent research results on this topic with focus on the advantages, current limitations, and future directions of flow chemistry.

Recent Advances in Continuous-Flow Enantioselective Catalysis.

The increased demand for more efficient, safe, and green production in fine chemical and pharmaceutical industry calls for the development of continuous-flow manufacturing, and for chiral chemicals in particular, enantioselective catalytic processes. In recent years, this emerging direction has received considerable attention and has seen rapid progress. In most cases, catalytic enantioselective flow processes using homogeneous, heterogeneous, or enzymatic catalysts have shown significant advantages over the conventional batch mode, such as shortened reaction times, lower catalysts loadings, and higher selectivities in addition to the normal merits of non-enantioselective flow operations. In this Minireview, the advancements, key strategies, methods, and technologies developed the last six years as well as remaining challenges are summarized.