已知:3a-b+|a2-49|a+7=0,则a=______,b=______.

题型:填空题

问题:

已知:
3a-b
+|a2-49|
a+7
=0,则a=______,b=______.
考点:绝对值
题型:填空题

E

Batteries can power anything from small sensors to large systems. While scientists are finding ways to make them smaller but even more powerful, problems can arise when these batteries are much larger and heavier than the devices themselves. University of Missouri (MU) researchers are developing a nuclear energy source that is smaller, lighter and more efficient.

"To provide enough power, we need certain methods with high energy density(密度)" ,said Jae Kwon, assistant professor of electrical and computer engineering at MU. "The radioisotope (放射性同位素) battery can provide power density that is much higher than chemical batteries. "

Kwon and his research team have been working on building a small nuclear battery, presently the size and thickness of a penny, intended to power various micro/nanoelectromechanical systems (M/NEMS). Although nuclear batteries can cause concerns, Kwon said they are safe.

"People hear the word ’ nuclear’ and think of something very dangerous," he said, "However, nuclear power sources have already been safely powering a variety of devices, such as pace-makers, space satellites and underwater systems. "

His new idea is not only in the battery’ s size, but also in its semiconductor(半导体). Kwon’ s battery uses a liquid semiconductor rather than a solid semiconductor.

"The key part of using a radioactive battery is that when you harvest the energy, part of the ra- diation energy can damage the lattice structure (晶体结构) of the solid semiconductor," Kwon said, "By using a liquid semiconductor, we believe we can minimize that problem. "

Together with J. David Robertson, chemistry professor and associate director of the MU Re- search Reactor, Kwon is working to build and test the battery. In the future, they hope to increase the battery’ s power, shrink its size and try with various other materials. Kwon said that battery could be thinner than the thickness of human hair.

Which of the following is true of Jae Kwon().

A. He teaches chemistry at MU.

B. He developed a chemical battery.

C. He is working on a nuclear energy source.

D. He made a breakthrough in computer engineering.

题型:填空题

一个梯形的上底、下底、高都是整厘米数,上底、下底与高的乘积分别为12和21,这个梯形的面积是______平方厘米.

题型:填空题

硬盘的跳线主要用于控制硬盘的主、从盘状态,表示设置驱动器主盘的选项为()

A.Master or single drive

B.Drive is slave

C.Master with a non-ATA compatibleslave

D.Cable select

题型:填空题

如图,网格纸上小正方形的边长为1,粗实现画出的是某多面体的三视图,则该多面体的表面积为()。

A.

B.

C.90

D.81

题型:填空题

无论是固定资产还是无形资产,都在取得的当月开始计提折旧或者摊销成本,处置的当月不再计提折旧或摊销成本。 ( )

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