A股纳入摩根斯坦利国际资本(Morgan Stanley Capital International,MSCI)新兴市场指数(入摩)是中国证券市场国际化的重大事件。研究这一事件的影响对日后持续推进我国资本市场的对外开放、制度创新有重要的现实意义。本文提出改进的事...A股纳入摩根斯坦利国际资本(Morgan Stanley Capital International,MSCI)新兴市场指数(入摩)是中国证券市场国际化的重大事件。研究这一事件的影响对日后持续推进我国资本市场的对外开放、制度创新有重要的现实意义。本文提出改进的事件研究法来客观地捕捉A股“入摩”及其首次扩容的事件窗口,进而划分事件影响的前后时间区间。随后,利用带格兰杰因果关系检验的多元随机波动(Grangercausality-Multiple Stochastic Volatility,GC-MSV)模型及条件自回归极差(Conditional Autoregressive Range,CARR)模型对A股“入摩”事件下内地与香港股市间的波动溢出关系进行研究。实证分析结果表明,内地与香港股市之间存在双向的波动溢出效应;首次纳入时的事件窗口较首次扩容的事件窗口持续时间更长,市场在首次纳入时反应更为强烈;在不同风险水平下,两市场间的波动溢出概率得到提高且逐渐趋于稳定;尤其在市场的低波动时期,内地股市对风险的敏感度显著提高;A股“入摩”使得内地股市对香港股市的波动溢出效应逐渐增强,两个市场之间的影响逐步趋同。展开更多
Maize (Zea mays L.) is the world’s leading cereal crop, with production estimated at over 1 billion tonnes in 2022. In Côte d’Ivoire, maize is one of the most widely consumed foods, with national production exc...Maize (Zea mays L.) is the world’s leading cereal crop, with production estimated at over 1 billion tonnes in 2022. In Côte d’Ivoire, maize is one of the most widely consumed foods, with national production exceeding 1 million tonnes in 2022. Despite its importance, this crop is subject to numerous biotic constraints, including Maize streak virus (MSV). The objective of this study was to characterize MSV isolates from Côte d’Ivoire using molecular biology techniques. To achieve this, maize leaf samples displaying characteristic symptoms of MSV were collected from different agro-ecological zones (AEZs) of Côte d’Ivoire. Total DNA was extracted from the collected samples using the CTAB method and quantified with a Nanodrop spectrophotometer. The C2 region of the MSV genome’s open reading frame (ORF) was amplified through polymerase chain reaction (PCR) using MSV-specific primers. The resulting PCR products were sequenced using the Sanger method. Bioinformatics analysis was performed using MSV sequences from other African countries (retrieved from NCBI) alongside sequences obtained in this study. The analysis was conducted using MEGA X version 10.05 software. The results showed that the main symptoms observed in the field included the presence of longitudinal light green streaks on leaves, stunted plant growth, and incomplete seed development in infected plants. Phylogenetic analysis of the sequences from Côte d’Ivoire revealed three monophyletic groups, with sequences of some isolates collected from the same plot belonging to different groups. The MSV sequences from Côte d’Ivoire are very close to those from Rwanda. This study underscores the need for further investigation into the genetic diversity of MSV strains to enhance the diagnosis and management of this viral disease, which is particularly prevalent in maize crops in Côte d’Ivoire.展开更多
文摘A股纳入摩根斯坦利国际资本(Morgan Stanley Capital International,MSCI)新兴市场指数(入摩)是中国证券市场国际化的重大事件。研究这一事件的影响对日后持续推进我国资本市场的对外开放、制度创新有重要的现实意义。本文提出改进的事件研究法来客观地捕捉A股“入摩”及其首次扩容的事件窗口,进而划分事件影响的前后时间区间。随后,利用带格兰杰因果关系检验的多元随机波动(Grangercausality-Multiple Stochastic Volatility,GC-MSV)模型及条件自回归极差(Conditional Autoregressive Range,CARR)模型对A股“入摩”事件下内地与香港股市间的波动溢出关系进行研究。实证分析结果表明,内地与香港股市之间存在双向的波动溢出效应;首次纳入时的事件窗口较首次扩容的事件窗口持续时间更长,市场在首次纳入时反应更为强烈;在不同风险水平下,两市场间的波动溢出概率得到提高且逐渐趋于稳定;尤其在市场的低波动时期,内地股市对风险的敏感度显著提高;A股“入摩”使得内地股市对香港股市的波动溢出效应逐渐增强,两个市场之间的影响逐步趋同。
文摘Maize (Zea mays L.) is the world’s leading cereal crop, with production estimated at over 1 billion tonnes in 2022. In Côte d’Ivoire, maize is one of the most widely consumed foods, with national production exceeding 1 million tonnes in 2022. Despite its importance, this crop is subject to numerous biotic constraints, including Maize streak virus (MSV). The objective of this study was to characterize MSV isolates from Côte d’Ivoire using molecular biology techniques. To achieve this, maize leaf samples displaying characteristic symptoms of MSV were collected from different agro-ecological zones (AEZs) of Côte d’Ivoire. Total DNA was extracted from the collected samples using the CTAB method and quantified with a Nanodrop spectrophotometer. The C2 region of the MSV genome’s open reading frame (ORF) was amplified through polymerase chain reaction (PCR) using MSV-specific primers. The resulting PCR products were sequenced using the Sanger method. Bioinformatics analysis was performed using MSV sequences from other African countries (retrieved from NCBI) alongside sequences obtained in this study. The analysis was conducted using MEGA X version 10.05 software. The results showed that the main symptoms observed in the field included the presence of longitudinal light green streaks on leaves, stunted plant growth, and incomplete seed development in infected plants. Phylogenetic analysis of the sequences from Côte d’Ivoire revealed three monophyletic groups, with sequences of some isolates collected from the same plot belonging to different groups. The MSV sequences from Côte d’Ivoire are very close to those from Rwanda. This study underscores the need for further investigation into the genetic diversity of MSV strains to enhance the diagnosis and management of this viral disease, which is particularly prevalent in maize crops in Côte d’Ivoire.
