问题 问答题 简答题

什么是白噪声?其频谱和自相关函数有什么特点?白噪声通过理想低通或理想带通滤波器后情况如何?

答案

参考答案:

噪声的功率谱密度在所有频率上均为一常数,则称为白噪声。

频谱为一常数,自相关函数只在R(0)处为∞。

白噪声通过理想低通和理想带通滤波器后分别变为带限白噪声和窄带高斯白噪声。

解答题
阅读理解

阅读下面的短文,并根据短文后的要求答题。

According to a new survey, students’ safety has become a big problem. Nearly 50% of students say they are worried about robbery on the way to and from school. Now in many big cities in China, some schools have taught an unusual lesson: self-protection. Students like this lesson because there are no exams or boring classes. And they can learn how to save lives and know how to stop danger before it really happens.

Chen Haoyu, a teacher at Beijing No. 25 Middle School, gives young students advice on how they should deal with danger.

If you are robbed

Keep calm. If you cannot cry for help or run away, give the robber your money. Try to remember what the robber looks like and tell the police later.

If you are in a traffic accident

If a car hurts you, you should remember the car number. If it is a bicycle, try to call your parents before you let the rider go. This is because you don’t know how seriously you are hurt.

If it is raining hard and there is lightning

Don’t stay in high places and stay away from trees.

When there is a fire

Get away as fast as you can. Put wet things on your body and try to find an exit. Do not take the lift.

If someone is drowning

If you can’t swim, don’t get into the water. Cry out for help.

Remember that danger is never as far away as you think. Take care of yourself at all times!

小题1:将文中划线句子翻译成汉语:                 

根据短文内容回答问题。

小题2:Why do students like the self-protection lesson?  

                               

小题3:How many suggestions for dealing with danger did Chen Haoyu give ? 

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小题4:What should you do when there is a fire?

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小题5:The best title for this passage might be