从象形文字的产生到埃及人丈量尼罗河两岸的土地，从航天飞机的问世到火星探测器对 火星形貌的探测，始终与图形有着密切关系，图形的重要性可以说是别的任何表达方法所不 能替代的 。现代图学教育可以为新世纪各类专门人才的图学素质培养及创新思维训练提供 方法

流体(Flurid)与流体流动(Flow)的基本概念 在航空、航天、航海,石油、化工、能源、环境、材料、医 学和生命科学等领域,尤其是化工、石油、制药、生物、食 品、轻工、材料等许多生产领域以及环境保护和市政工程等, 涉及的对象多为流体

项目管理产生于第二次世界大战期间,它作 为一门学科和一种特定的管理方法最早起源于 美国; 早期,美国将项目管理应用于大型军事项 目、航天工程与开发工业等项目上,如:曼哈 顿原子计划、北极星导弹计划、阿波罗宇宙飞 船载人登月计划及石油化工系统中

Cyclic Codes a cyclic code is a linear block code where if c is a codeword, so are all cyclic shifts of c E.g., 1000, 110, 101,011 is a cyclic code Cyclic codes can be dealt with in the very same way as all other lbc s Generator and parity check matrix can be found a cyclic code can be completely described by a generator string G All codewords are multiples of the generator string In practice, cyclic codes are often used for error detection(CRc) Used for packet networks When an error is detected by the received, it requests retransmission

Channel Coding When transmitting over a noisy channel, some of the bits are received with errors Example: Binary Symmetric Channel (BSc) Pe= probability oferror Q: How can these errors be removed? A: Coding: the addition of redundant bits that help us determine what was sent with greater accuracy

Noise is additional\unwanted \signal that interferes with the transmitted signal Generated by electronic devices The noise is a random process Each\sample \ of n(tis a random variable Typically, the noise process is modeled as\Additive White Gaussian noise”(AWGN) White: Flat frequency spectrur Gaussian noise distribution

Modulation Representing digital signals as analog waveforms Baseband signals Signals whose frequency components are concentrated around zero Passband signals Signals whose frequency components are centered at some frequency fc away from zero Baseband signals can be converted to passband signals through modulation Multiplication by a sinusoid with frequency fc Eytan Modiano

Information content of a random variable Random variable x Outcome of a random experiment Discrete R V takes on values from a finite set of possible outcomes PMF: P(X=y)=Py) How much information is contained in the event X=y? Will the sun rise today Revealing the outcome of this experiment provides no information Will the Celtics win the NBa championship? Since this is unlikely, revealing yes provides more information than revealing Events that are less likely contain more information than likely events

第10章液压传动 液压传动是以液体作为工作介质,并利用液体的压力实现机械设备的运动或能量传递和控制功能,随着现代科技的发展,液压传动在机床、工程机械、交通运输机械、农业机械、化工机械、船舶及航空航天等领域都得到了广泛的应用。 10.1液压传动的基本知识 10.2液压元件 10.3液压基本回路及液压系统 10.4液压传动系统的拆装与分析(一) 10.5液压传动系统的拆装与分析(二)

计算机绘图软件之一,在机械、建筑、汽 车、电子、航天、造船、地质、服装等多个领域得到了广泛应用,因为其适用面之 退出广、拥有强大的绘图功能,受到了工程技 术人员的青睐