Today you can get an iPod nano for $179 that’s a fraction of the original iPod’s size and weight, with double the storage, a color display, video playback, and a built-in video camera.

今天你可以只花179美元就能得到一个iPod nano，今天的产品只是最初的iPod大小和重量的一小部分，但是会有最初的两倍的存储容量，彩色的显示屏，能录放而且还有一个内置的摄像头。

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The perceptron training rule is based on the idea that weight modification is best determined by some fraction of the difference between target and output.

感知器培训规则是基于这样一种思路—权系数的调整是由目标和输出的差分方程表达式决定。

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There are many, but one plausible rule is based on the idea that weight and threshold modification should be determined by a fraction of (t - y).

有很多，不过有一条似乎合理的规则是基于这样一种思想，即权系数和阈值的调整应该由分式(t - y)确定。

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That might not seem like much, but considering most rigid robot arms can only lift a fraction of their own weight, it represents a sizable gain in strength-to-weight ratio.

ENGADGET: iRobot's AIRarm prototype bot has an inflatable arm for manipulating objects, was built at DARPA's behest

The NX20 is the perfect match for enthusiast amateur or professional photographers looking for a highly portable camera that gives the professional look and feel of a DSLR but at a fraction of the size and weight, with the addition of an ergonomic grip to fit comfortably into the hand.

ENGADGET: Samsung's NX20, NX210 and NX1000 mirrorless camera trio hands-on (video)