To remind ourselves that we are doing it along a closed curve, very often we put just a circle for the integral to tell us this is a curve that closes on itself.
为了提醒我们是在封闭曲线上做积分，经常在积分符号上加个圆圈，告诉我们，这条曲线自我封闭。
He is most famous for the play Death of a Salesman, which was put on stage in 1949 and won both a Pulitzer Prize and a Drama Critics Circle Award.
他的代表作《推销员之死》于1949年面世，曾获得普利策奖和戏剧评论界奖。
The measurement system on chain board of tooth shape chain was established based on computer vision, and a new kind of sub-pixel algorithm for edge orientation of beeline and circle was put forward.
构建了基于计算机视觉的齿形链链板的测量系统，对直线和圆的边缘定位，提出了新的亚像素算法，计算了齿形链链板的销孔直径及圆度误差、链板节距和两直边夹角，对测量结果进行了误差分析。
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