CSMA/CD and Ethernet Two way cable wsws Ws W CSMA with Collision Detection(CD)capability Nodes able to detect collisions Upon detection of a collision nodes stop transmission Reduce the amount of time wasted on collisions Protocol

新药的创制是一个系统工程,在研究与开发的 过程中,涉及了多种学科与领域,包括有分子生物 学,生物信息学、分子药理学、药物化学、计算机 科学、以及药物分析化学、药理学、毒理学、药剂 学、制药工艺学等。这些环节的有机配合,可以促 进新药研制的质量与速度,使创制的新药更具有安 全性、有效性和可控性

本章使学生了解果品蔬菜贮 藏效果的好坏乃至贮藏成败与否,除与 采收、分级、包装、贮藏管理等采后技 术密切相关外,而且还受产品本身的生 物学特性、栽培的生态条件、田间的农 业技术措施等采前因素的制约,从而认 识到果品蔬菜的贮藏保鲜是一项技术性 很强的系统工程

根据特定的育种目标，制定出在多项育种措施 上具有不同强度的候选育种方案，通过育种成 效标准，如综合遗传进展、育种效益等，进行 综合评估，应用系统工程的方法，科学有效地 配置资源、技术、方法和措施，筛选出“最优 化”（optimization）育种方案

Used for analyzing network performance In packet networks, events are random Random packet arrivals Random packet lengths While at the physical layer we were concerned with bit-error-rate, at the network layer we care about delays How long does a packet spend waiting in buffers?

要做好市场调查这项系统工程，首 先必须搞好规划。在整体规划中，市 场调查方案的设计是一个非常重要和 必须的工作。本章主要介绍了用户市 场信息需求分析、调查课题的确定、 调查方案的内容等问题，提供了市场 调查方案的撰写方法和可行性研究方 法

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

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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

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