Research on Two-Step Hydro-Bulge Forming of Ellipsoidal Shell with Larger Axis Length Ratio

The two-step hydro-bulge forming technique was proposed to manufacture the ellipsoidal shell with the length ratio of the long axis to the short axis larger than 1.4. A central tube was introduced into the first step of the hydro-bulge forming process to constrain the over growth of the short axis during bulging,and then the central tube was replaced with two polar plates in the second step of the hydro-bulge forming process to manufacture an integral ellipsoidal shell. It is shown that the central tube restricts the growth of the short axis and simultaneously reduces the shrunk tendency of the long axis. The wrinkling occurs due to the latitudinal compressive stress at the equator at the early stage of hydro-bulge forming. However,with the increase of internal pressure,the compressive stress areas gradually decrease and finally the tensile latitudinal stress occupies approximately the whole shell,thus the wrinkles are eliminated. A sound ellipsoidal shell with the axis length ratio of 1.8 is obtained after two-step hydro bulging.

关于昌平区城区低龄儿童视力发育特点的初步研究

目的本文主要对昌平区城区学龄前期及学龄期儿童的视力发育特点进行初步研究。方法入选2016年3月-2017年12月在昌平区医院眼科门诊筛查视力的儿童,共计123人246眼进行屈光发育健康档案的建立,全部儿童均进行视力、屈光度、眼轴测量,分析筛查结果。结果发现裸眼视力低常者共计45人90眼;其中近视的儿童为24人,占裸眼视力低常者的53.3%,远视的儿童为21人,占裸眼视力低常者的46.7%。其中弱视的儿童为6人,占所有受检儿童的4.9%;24人近视的儿童中,儿童的眼轴长度平均为(23.30±1.14)mm,21人远视的儿童中,儿童的眼轴长度平均为(21.86±0.53)mm。结论昌平区城区低龄儿童的视力存在一定问题,应建立屈光健康档案,定期进行视力监测,并给予相应的防治措施。