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Cases of the flu peak in winter in the U.S., but why? A new study suggests it's not the heat, but huminity. Or lack thereof. Because in temperate¹ regions, the influenza² virus fares best when the weather's dry. That's according to work published in the journal PLoS One.

Scientists have long debated why flu erupts when the days grow chilly³. Is it that we spent more time cooped up together indoors? Or is there something about the virus likes it cold and dry? To find out, researchers suspended influenza virus in a solution that mimics⁴ human mucus. They incubated this infectious soup at different huminities and measured viral survival.

And they found that at low huminity, the fake mucus dries up and the virus does just fine. But when the humidity tops 15 percent, the droplets⁵ only partially⁶ evaporate, leaving behind a solution that’s too salty for the virus to thrive.

Interestingly, the virus does well again when the humidity reaches 100 percent. Evaporation⁷ stops and this humidity of the mucus bath is just right. That could explain why the flu prefers to hit the tropics in rainy season and why you should always keep your nose clean, but moist.

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1 temperate
adj.温和的，温带的，自我克制的，不过分的
参考例句：
Asia extends across the frigid,temperate and tropical zones.亚洲地跨寒、温、热三带。 Great Britain has a temperate climate.英国气候温和。

2 influenza
n.流行性感冒，流感
参考例句：
They took steps to prevent the spread of influenza.他们采取措施 Influenza is an infectious disease.流感是一种传染病。

3 chilly
adj.凉快的，寒冷的
参考例句：
I feel chilly without a coat.我由于没有穿大衣而感到凉飕飕的。 I grew chilly when the fire went out.炉火熄灭后，寒气逼人。

4 mimics
n.模仿名人言行的娱乐演员，滑稽剧演员( mimic的名词复数 )；善于模仿的人或物v.（尤指为了逗乐而）模仿( mimic的第三人称单数 )；酷似
参考例句：
Methods:Models were generate by CT scan,Mimics software and Abaqus software. 方法：采用CT扫描，Mimics软件和Abaqus软件的CAD进行三维有限元模型的创建。来自互联网 Relaxing the mind and body mimics the effect that some blood-pressure pills would have. 放松身心会产生某些降压药才能产生的效果。来自辞典例句

5 droplets
n.小滴( droplet的名词复数 )
参考例句：
Droplets of sweat were welling up on his forehead. 他额头上冒出了滴滴汗珠。来自辞典例句 In constrast, exhaled smoke contains relatively large water droplets and appears white. 相反，从人嘴里呼出的烟则包含相当大的水滴，所以呈白色。来自辞典例句

6 partially
adv.部分地，从某些方面讲
参考例句：
The door was partially concealed by the drapes.门有一部分被门帘遮住了。 The police managed to restore calm and the curfew was partially lifted.警方设法恢复了平静，宵禁部分解除。

7 evaporation
n.蒸发，消失
参考例句：
Be careful not to lose too much liquid by evaporation.小心不要因蒸发失去太多水分。 Our bodies can sweat,thereby losing heat by evaporation.我们的身体能出汗，由此可以蒸发散热。