研究人类迁移的学生们谈到“推”和“拉”因素，这些因素会影响个体是否会从一个地方迁移到另一个地方。
Students of human migration speak of "push" and "pull" factors, which influence an individual's decision to move from one place to another.
通过结合这三个因素，拉波波特创造出一个数学公式，这个公式可以让任何体型的运动员知道跑多远和多快才能避免‘速度障碍’。
By combining these factors, Rapoport created a mathematical model of how long and how fast runners of any size can go without hitting the wall.
计算机模拟能把这些因素进行综合考量。这能改进设计出可折叠或是能拉货的自行车。
Computer simulations that take all of these factors into account could lead to improved designs for folding bikes with small wheels or bikes that carry cargo, Ruina says.
应用推荐