Chapter 2 Aerodynamics: Some Fundamental Principles and Equations There is so great a difference between a fluid and a collection of solid particles that the laws of pressure and of equilibrium of fluids are very different from the laws of the pressure and equilibrium of solids Jean Le Rond d' Alembert, 1768

0644液压传动的动力元件通常是指 A.油泵B.油马达C.油缸D.A+B0645液压马达是将能变为能。 A.电,液压B.液压,机械C.机械,液压D.电,机械

0001下列泵中属于叶轮式泵的是 A.齿轮泵B.叶片泵 C.水环泵D.旋涡泵 0002不属于回转式容积式泵的是 A.水环泵B.齿轮泵C.螺杆泵D.旋涡泵 0003属于回转式容积泵的是 A.离心泵B.水环泵 C.旋涡泵D.轴流泵

1.一调光台灯由单相交流调压电路供电,设该台灯可看成电阻负载,在a=0°时输出功率为最 大值,试求功率为最大输出功率的80%、50%时的开通角a 2.一单相交流调压器,电源为工频220V,阻感串连作为负载,其中R=0.5Q,L=2mH试求: ①开通角a的变化范围;②负载电流的最大有效值③最大输出功率及此时电源侧的功率因数

Part I Vocabulary Structure (25%) Section a Directions: Complete each sentence by choosing the appropriate answer from the 4 choices 1. He said.\I a lot of new words by the end of last year A) had already learnt C)have already learnt B)would have already learnt D)already learnt

一、例题精解 【例题2.1】在图2.2所示方框图中,N是一线性无源网络。当U1=1V,2=1A时,U3=0V:当U1=10V,2=0A时,U3=1V.试求当U1=0V,I2=10A时,U3=? 【解】应用叠加原理计算,则U3=U3+U3。其中3=AU是U1单独作用时的分量,U3=B2是l2单独作用时的分量,即

once oncu n a paiuicuia positon on DNA, a nucleosome remained fixed in place because of the tight association 30-nm 98A5 sequence-specific DNA-binding proteins nucleosome

4.4向量空间 1.向量空间:设V是具有某些共同性质的n维向量的集合,若 对任意的a,B∈V,有a+B∈V;(加法封闭) 对任意的a∈V,k∈R,有ka∈V.(数乘封闭) 称集合为向量空间

Virus a noncellular genetic element that enlists a cell for its own replication, it has an extracellular state. A virus particle containing nucleic acid surrounded by protein and other macromolecular components is called virion

一、定积分计算 1.设f(x)=,edx,求xf(x)d 2.设A=,试用表示:(1)B= 1t-a-1 (2 (1+t) 3.设feC,,证明:f(d=(x-x2)f(x)d 4.计算定积分xln(1+e)dx 二、定积分应用 1.设有曲线族y=kx2(k>0),对于每个正数k(k2),曲线y=kx2 与曲线y=sinx(0≤xs)交于唯一的一点(t,sint)(其中t=t()) 用S1表示曲线y=kx2与曲线y=sinx(0≤x≤)围成的区域的面积; S2表示曲线y=sinx,y=sint与x=围成的区域的面积求证在上述 曲线族中存在唯一的一条曲线L,使得S1+S2达到最小值 2.点A(3,1,-1)是闭曲面S1:x2+y2+z2-2x-6y+4z=10