6-烯-8-羰基-1-叔丁氧基羰基氮杂螺[4,4]壬烷的合成

以烯丙基脯氨酸甲酯(1)为起始原料, 经7步反应以42%的总收率得到了三尖杉碱合成中的重要中间体6-烯-8-羰基-1-叔丁氧基羰基氮杂螺[4,4]壬烷(7). 关键反应为构筑螺环季碳的[2,3]斯蒂文森重排(Stevens rearrangement)及烯丙基双键加氧的酸内酯化反应(Acid-lactonization reaction).     

Outer synchronization between two different fractional-order general complex dynamical networks

Outer synchronization between two different fractional-order general complex dynamical networks is investigated in this paper.Based on the stability theory of the fractional-order system,the sufficient criteria for outer synchronization are derived analytically by applying the nonlinear control and the bidirectional coupling methods.The proposed synchronization method is applicable to almost all kinds of coupled fractional-order general complex dynamical networks.Neither a symmetric nor irreducible coupling configuration matrix is required.In addition,no constraint is imposed on the inner-coupling matrix.Numerical examples are also provided to demonstrate the validity of the presented synchronization scheme.Numeric evidence shows that both the feedback strength k and the fractional order α can be chosen appropriately to adjust the synchronization effect effectively.     

抗击算法偏见

2011年,在佐治亚理工学院读本科期间,计算机科学家Joy Buolamwini发现,她与机器人一起玩躲猫猫这个简单游戏是不可能的,因为这个机器人不能识别她黑肤色的脸。2015年,已是麻省理工学院媒体实验室硕士生的她也在人脸分析软件中遇到了类似的问题：只有当她带上一个白色面具的情况下,系统才能检测到她的脸。这是巧合吗？