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  1. Why divide by n-1 and not n?

    “Some questions are more easily asked than answered” Edward Sapir(?) Possibly the most frequently asked and least frequently answered question is why does the definition of the standard deviation involve division by n-1, when n might seem the obvious choice. This is a question which perplexes introductory statistics students and calculator manufacturers alike. The explanations Continue reading...

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  2. 什么是SSH (Secure Shell) ?

    转自泰克Cisco网络技术论坛 传统的网络服务程序，如:ftp、pop和telnet在本质上都是不安全的，因为它们在 网络上用明文传送口令和数据，别有用心的人非常容易就可以截获这些口令和数据。而且，这些服务程序的安全验证方式也是有其弱点的，就是很容易受到"中间人 "(man-in-the-middle)这种方式的攻击。所谓"中间人"的攻击方式，就是"中间人"冒充真正的服务器接收你的传给服务器的数据，然后再 冒充你把数据传给真正的服务器。服务器和你之间的数据传送被"中间人"一转手做了手脚之后，就会出现很严重的问题。 SSH的英文全称是Secure SHell。通过使用SSH，你可以把所有传输的数据进行加密，这样"中间人"这种攻击方式就不可能实现了，而且也能够防止DNS和IP欺骗。还有一个额 外的好处就是传输的数据是经过压缩的，所以可以加快传输的速度。SSH有很多功能，它既可以代替telnet，又可以为ftp、pop、甚至ppp提供一 个安全的"通道"。 Continue reading...

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  3. 雷鸟(Thunderbirds)

    美国空军的雷鸟(Thunderbird) F-16战机正编队飞过肯尼迪航天中心的车辆装配大楼。在今年末，雷鸟将会出现在肯尼迪航天中心举办的世界航天博览会开幕周的飞行表演中。此次博览盛会将展出那些曾在同一地点聚集过的航空文物、装备和人物，同时它将是世界上最大的航空展出之一。 图像来自：U.S. Air Force/TSgt. Justin D. Pyle Continue reading...

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  9. During the orientation days

    During the orientation days, I took part in many activities such as BBQ, lecture for new students, outgoing… It’s really relax during this period, but I believe the terrible time will soon come to me. I have many many courses per week, just cuz my major is Computer Science. Don’t like those ppl studying business, Continue reading...

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