问题 问答题 简答题

计算题:用2.5MHZ纵波直探头接触法探测复合钢板,已知不锈钢声阻抗为45.8×106Kg/m2S,碳素钢声阻抗为46×106kg/m2S,求复合界面反射率,透过率及界面与底面在示波屏上回波的dB差。(假定复合面完全粘合,不考虑衰减、扩散及表面反射损失)?

答案

参考答案:

γp=│(45.8-46)/(46+45.8)│

=0.00217864×100%=0.217864%

tp=│(2×45.8)/(46+45.8)│

=0.9978×100%=99.78%

ΔdB=20lg[γp/(1-γp2)]

=20lg[0.00217864/(1-0.002178642)]

=-53dB

反射率γp=0.217864%,透过率tp=99.78%,界面与底面在示波屏上回波的dB差为53dB。

判断题
阅读理解

Alone in the darkness under layers of rubble (碎石) , Dan Woolley felt blood streaming from his head and leg.

Woolley, an aid worker, husband, and father of two boys, followed instructions on his cell phone to survive the January 12 earthquake in Haiti.

“I had an app that had pre-downloaded all this information about treating wounds. So I  looked up excessive bleeding and I looked up compound fracture(断裂),” Woolley told CNN.

The application on his iPhone is filled with information about first aid and CPR from the American Heart Association. “So I knew I wasn’t making mistakes, ” Woolley said. “That gave me confidence to treat my wounds properly.”

Trapped in the ruins of the Hotel Montana in Port-au-Prince, he used his shirt to bandage his leg, and tied his belt around the wound. To stop the bleeding on his head, he firmly pressed a sock to it. Concerned he might have been experiencing shock, Woolley used the app to look up what to do. It warned him not to sleep. So he set his phone alarm to go off every 20 minutes.

Once the battery got down to less than 20 percent of its power, Woolley turned it off. By then, he says, he had trained his body not to sleep for long periods, drifting off only to wake up within minutes.

With his injuries tended to, he wrote a note to his family in his journal: “I was in a big accident, an earthquake. Don’t be upset at God. He always provides for his children even in hard times. I’m still praying that God will get me out, but he may not. But even so he will always take care of you.”

After more than 60 hours, Woolley was pulled from the rubble.

“Those guys are rescue heroes,” he said to the crew that pulled him out.

小题1: Which of the following best summarizes the passage?

A.How to deal with the wound.

B.Try to get in touch with outside.

C.How to stay awake under the ground.

D.An unforgettable experience in the earthquake.小题2:Woolley set his phone alarm to go off every 20 minutes because_____.

A.he tried his best to communicate with rescuers

B.he was forced to stay awake to check his wounds

C.he was afraid that sleep might do harm to him

D.he needed to use the app to look up what to do小题3:The underlined sentence suggests that_________.

A.he turned off his iPhone to save power

B.the battery of his IPhone lasted long

C.he didn’t want his iPhone to disturb him

D.his iPhone went off because of lack of power小题4: What Woolley wrote his journal showed _______.

A.he expected his family to lend a hand

B.he didn’t lose heart in hard times

C.he cared more for his family than his life

D.his children made him upset