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Based on the reconstructed precipitation series in North China from historical documents, the 1876-1878 drought was identified as the most severe and extreme one in North China over the past 300 years. Meanwhile, the spatial patterns of seasonal and annual precipitation during 1876-1877 were analyzed and the social and economic impacts related with this drought event were evaluated according to the descriptions in the historical documents. The results indicated that this long-lasting drought started by the spring of 1876 and did not stop until the spring of 1878. Within the three years, the harvest failures brought the rice price increased to 5-10 times than that in the normal year, and the total population in the five provinces over North China decreased by more than 20 million due to a large number of dead people and migrations. In addition, related investigations suggested that the 1876-1878 drought was prevalent worldwide, which has possible link with abnormal high SST in the equatorial central and eastern Pacific, strong El Niño episode and positive AAO anomalies. 1876-1878, severe drought, North China, social impact, climatic background Citation:Drought is one of the most important natural hazards. Long-lasting droughts usually result in water shortage and degradation of ecosystem functions [1,2] and even hinder the progress of human civilization [3]. When the scientific community of global change is paying attention to the possible effect of increasing greenhouse gases on the future climate, it is pertinent for us to look back into the history to examine the extreme climatic events over the past few centuries to millennia and their social impacts [4].North China is located in the warm temperate and sub-humid zone and subject to the influence of East Asian summer monsoon, where the climate condition is characterized by large inter-annual precipitation variability and frequent droughts and floods. Moreover, this region has been the most populous in China since the ancient times, and major climatic anomalies, such as long-lasting droughts, will bring serious impacts on agriculture, people's life and socioeconomic development. Therefore, the emperors during the ancient dynasties were very concerned about the occurrence of droughts and floods, and historical archives recorded detailed information about disasters' intensity, spatial coverage and social impacts. The previous related studies showed that there were four major continuous droughts in North China over the past 500 years, and they occurred during

Periodontal regeneration involves the restoration of at least three unique tissues: cementum, periodontal ligament tissue (PDL) and alveolar bone tissue. Here, we first isolated human PDL stem cells (PDLSCs) and jaw bone mesenchymal stem cells (JBMSCs). These cells were then induced to form cell sheets using an ascorbic acid-rich approach, and the cell sheet properties, including morphology, thickness and gene expression profile, were compared. Platelet-rich fibrin (PRF) derived from human venous blood was then fabricated into bioabsorbable fibrin scaffolds containing various growth factors. Finally, the in vivo potential of a cell-material construct based on PDLSC sheets, PRF scaffolds and JBMSC sheets to form periodontal tissue was assessed in a nude mouse model. In this model, PDLSC sheet/PRF/JBMSC sheet composites were placed in a simulated periodontal space comprising human treated dentin matrix (TDM) and hydroxyapatite (HA)/tricalcium phosphate (TCP) frameworks. Eight weeks after implantation, the PDLSC sheets tended to develop into PDL-like tissues, while the JBMSC sheets tended to produce predominantly bone-like tissues. In addition, the PDLSC sheet/PRF/JBMSC sheet composites generated periodontal tissue-like structures containing PDL- and bone-like tissues. Further improvements in this cell transplantation design may have the potential to provide an effective approach for future periodontal tissue regeneration.

Although the included studies had high heterogeneity, meta-analysis provided some evidence that mirror therapy may significantly improve motor function of the upper limb in patients with stroke. Further well-designed studies are needed.

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