且由于在另一个星系中的单颗“造父变星”的亮度就足于使其被观测到，所以它们是测算类似星系距离的首选工具。
And, since individual Cepheids are bright enough to be seen in other galaxies, they were the first tool used to estimate the distances to such galaxies.
诺达公司的产品主要包括高分子材料加工用多种类型单/双螺杆挤出机系列、配混造粒成套设备、塑料片材/板材/薄膜设备、高分子材料回收设备等。
Norda mainly supplies polymer - purposed single screw / twin screw extruders, compounding and granulating systems, plastic sheets / plates / films extrusion lines and polymer recycling systems.
结果：2例经输尿管镜逆行放置两侧输尿管双猪尾导管内引流，17例经皮肾穿刺造瘘和扩张后于单侧输尿管放置两根不同直径的双猪尾导管内引流。
RESULTS: Bilateral retrograde placement of double pigtail stent was performed in 2 cases. Indwelling different size double pigtail stents in unilateral ureters were carried out in 17 cases.
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