How to keep windows clear using gold and sunlight.

如何用金和阳光让窗户保持干净。

As the northern hemisphere’s winter arrives, the problem of fogged-up car windscreens becomes more pressing for drivers.

随着北半球冬季的到来，汽车挡风玻璃结雾成为了司机们亟待解决的问题。

When humid air hits a surface colder than it is, the water vapour it carries condenses onto that surface as myriad tiny droplets.

潮湿的空气接触到比自身更冷的表面时，它携带的水蒸气会凝结到该表面上，形成无数微小的水滴。

It is the filling that warms the glass.

能让玻璃变暖的是三明治中间的馅料。

When gold is deposited onto a surface at random, it first forms miniature islands.

当金随机沉积到一个表面上时，先会形成一些微型岛屿。

Since these are not connected to each other, the result is an insulator.

它们彼此之间互不连接，因此成为了绝缘体。

Then, as more gold is added, bridges form between the islands.

然后，随着更多金的出现，岛屿之间就架起了桥梁。

At a certain point these bridges transform the developing network from an insulator into a conductor, by letting electrons hop from island to island.

在某一时刻，这些桥梁让电子从一个岛屿来到另一个岛屿，将发展中的网络从绝缘体转变为导体。

That permits heat to spread.

热量因此得以传播。

The network will now, like any other metal, absorb heat if left in the sunshine.

现在在阳光下，它能像其它任何金属一样吸收热量。

It does so best, Mr. Hachler and Dr. Poulikakos say, when it reaches the so-called percolation limit - the moment at which it switches from an archipelago to an electrically interconnected sheet.

哈克勒先生和普利卡科斯博士说，当材料达到所谓的“渗流极限”，也就是从无数岛屿转变为一个电互连的薄片时，除雾效果是最好的。

The titanium-dioxide layers boost that absorption.

二氧化钛层促进了热量吸收。

This substance has a high refractive index, meaning the speed of light passing through it is greatly reduced.

这种物质的折射率很高，意味着光穿过它的速度会大幅降低。

That prolongs the time such light can interact with (and thus heat up) the gold.

这延长了光与金相互作用（从而进行加热）的时间。

The upper layer of titanium dioxide also protects the gold beneath it from damage.

上层的二氧化钛也能保护中间的金不受损害。

Glass coated with Mr. Hachler’s and Dr. Poulikakos’s invention is, they claim, four times more effective at preventing fog than an uncoated surface.

哈克勒先生和普利卡科斯博士声称，涂有他们发明涂层的玻璃防雾效果是无涂层玻璃的四倍。

It absorbs around 30% of solar radiation incident upon it - which, on a sunny day, increases the temperature of what it is applied to by around 8°C.

该涂层能够吸收入射太阳辐射的大约30%——这意味着在晴天，涂有涂层的表面温度能够上升约8摄氏度。

On a cloudy day, that temperature rise is closer to 3-4°C.

而在阴天，温度上升更接近3-4摄氏度。

But in either case the enhancement is sufficient both to remove any fog that has condensed and to prevent new fog forming.

无论是什么天气，这种程度的温度上升都足以消除已经凝结的雾，并防止雾的形成。

The main problem is that it does not work at night.

主要问题在于，这种涂层在晚上不能工作。

The next step, Mr. Hachler says, is to find the product’s best market.

哈克勒先生说，下一步是找到最适合该产品的市场。

Dr. Poulikakos reckons spectacles are a good starting point.

普利卡科斯博士认为，眼镜是一个很好的起点。

(This is not an entirely disinterested suggestion, for he wears them himself.）

（这个建议并不是很客观，因为他自己也戴眼镜）。

Spectacle lenses already have many layers of coatings applied to them.

眼镜镜片已经包含很多层涂层。

The cost of adding this extra one is low.

额外增加新涂层的成本很低。

Even though gold is used, so little is required that the materials themselves are worth only 20 cents or so.

尽管涂层中使用了金，但含量很少，因此材料本身的价值只有20美分左右。

For the two inventors, though, the idea might prove a gold mine.

然而，对于这两位发明家来说，他们的想法可能会是一座金矿。

来源：经济学人