Google has confirmed the test is taking place but only in countries where location extensions (a system to filter and target certain keyword searches) are available.
Google证实这项测试正在进行中，但该测试只在可以提供地理位置扩展(一个可以过滤和针对特定搜索关键词搜索的系统)服务的国家中进行。
For starters, safely taking pictures of the sun requires a special solar filter on the camera.
对初学者来说，安全地拍摄太阳照片的相机上需要一个特殊的太阳滤波器。
This paper introduces the basic methods for designing the low-pass filter, taking Butterworth filter as an example.
文章以巴特沃思滤波器为例介绍低通滤波器的基本设计方法。
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