1、专 业 英 语,Specialized English,被动语态及其译法,科技英语中大量使用被动语态 科技英语所表达的是客观规律，要尽量避免使用主观色彩较强的第一、第二人称； 被动语态主要的信息置于句首，更能突出主要论证、说明对象，引人注目； 在很多情况下被动结构比主动结构更简短。,第一部分 专业英语基础知识,1.译成汉语被动句： 常用“被”、“受到”、“得到”、“让”、“给”、“把”、“使”、“由”等措辞。 A digital image is composed of a finite number of elements, each of which has a particular lo
2、cation and value. 数字图像由有限个元素（像素）构成，每个像素都具有特定的位置与数值。,被动语态的译法,2.译成汉语的主动句： 直接将原文的被动语态按照主动语态译成汉语的主动句。 The experiment will be finished in a month. 这项实验将在一个月后完成。 Using time multiplexing, a digital system can be used to process a number of digital signals. 利用时分复用技术，一个数字系统能处理多路数字信号。,被动语态的译法,3.译成汉语的加强语句： 当英语
3、被动句不是强调被动的动作，而只是强调或肯定某一事实或行为的存在时，通常可用“是的”或“为所”等句式来翻译此类句子。 These computers were made in Xinhua Company. 这些计算机是新华公司制造的。 The project was completed last year. 这个项目是去年完成的。,被动语态的译法,4.译成汉语的无主句： 在讲述什么事情时往往是强调如何去做，而不介意谁去做。对于这一类被动句的翻译，可以译为汉语的无主句。 The instrument must be handled with great care. 必须仔细操作这台仪器。,总之，
4、在翻译英语的被动句时，不能固守原句，要灵活地采用多种翻译技巧，使译文既在内容上忠实原文，又符合汉语的表达方式。,被动语态的译法,Unit 5：,第二部分 通信技术,The Sampling Theorem,抽样定理,Specialized English for Communication Engineering,NEW WORDS AND PHRASES,theorem n. 定理，定律，法则 exploit vt. 开拓，开发，利用 sequence n. 次序，顺序，序列 instantaneous adj. 瞬间的，即刻的，即时的 reproducible adj. 可再生的，可复制的
5、 cut off n. 截止，中止，切掉 replication n. 复制，重现 perceive v. 感知，感到，认识到 aliasing n. 混淆现象，混叠 Nyquist rate n. 奈奎斯特（抽样）速率,Specialized English for Communication Engineering,Under certain conditions, a continuous signal can be completely represented by and recoverable from a sequence of its values, or samples, a
6、t points equally spaced in time. recoverable :可重获的 sequence :次序, 顺序, 序列 Space：留间隔， 隔开 在一定的条件下，一个连续时间信号完全可以由该信号在时间等间隔点上的瞬时值或样本值来表示，并且能用这些样本值恢复出原信号来。,TEXT,Specialized English for Communication Engineering,This somewhat surprising property follows from a basic result that is referred to as the sampling
7、 theorem. This theorem is extremely important and useful. somewhat :稍微, 有点, 有些 follow from：是从根据.得出的 saturate:饱和 这有点不可思议的性质是根据抽样定理这个基本结论得出的。这个理论及其重要且非常有用,Specialized English for Communication Engineering,It is exploited, for example, in moving pictures, which consist of a sequence of individual frame
8、s, each of which represents an instantaneous view (i.e., a sample in time) of a continuously changing scene. exploit: 使用,开拓, 开发, 开采 moving pictures : 活动图象, 电影 individual :个别的, 单独的, 个人的 frame: 帧,画面,框架 instantaneous: 瞬间的, 即刻的, 即时的 例如，抽样定理在电影里得到了利用。电影由一组按时序排列的单个画面所组成，其中每一个画面都代表着连续变化景象中的一个瞬时画面（即时间样本）。,S
9、pecialized English for Communication Engineering,When these samples are viewed in sequence at a sufficiently fast rate, we perceive an accurate representation of the original continuously moving scene. in sequence：顺次, 挨次 perceive：察觉，感知，感到 当我们以极快的速度来顺次观察这些瞬时画面时，感觉到的就是对原来连续活动场景的一个准确再现。,Specialized Eng
10、lish for Communication Engineering,Much of the importance of the sampling theorem also lies in its role as a bridge between continuous-time signals and discrete-time signals. continuous-time signals : 连续时间信号 discrete-time signals: 离散时间信号 抽样定理的重要性很大程度上体现在：它起着连续时间信号和离散时间信号之间的桥梁的作用。,Specialized English
11、 for Communication Engineering,The fact that under certain conditions a continuous-time signal can be completely recovered from a sequence of its samples provides a mechanism for representing a continuous-time signal by a discrete-time signal. recover：重获，恢复，复原 sequence：序列，顺序, 次序 mechanism ：机理， 机构, 机
12、制 在一定的条件下，可以用信号的时序样本值完全恢复出原连续时间信号，这就提供了用一个离散时间信号来表示一个连续时间信号的机理。,Specialized English for Communication Engineering,In many contexts, processing discrete-time signals is more flexible and is often preferable to processing continuous-time signals. be preferable to ：比更为可取， 更好, 更优越 在许多方面，处理离散时间信号要更加灵活些，因
13、此往往比处理连续时间更为可取。,Specialized English for Communication Engineering,This is due in large part to the dramatic development of digital technology over the past few decades, resulting in the availability of inexpensive, lightweight, programmable, and easily reproducible discrete-time signal, process the
14、discrete-time system. dramatic：引人注目的，戏剧性的, 生动的 lightweight ：重量轻的，轻质的 这在很大程度上是由于在过去几十年中数字技术的发展，导致了便宜的、轻质的，处理可编程且易于再生的离散时间信号的离散时间系统的实用化。,Specialized English for Communication Engineering,We exploit sampling to convert a continuous-time signal to a discrete-time signal, process the discrete-time signal
15、 using a discrete-time system, and then convert back to continuous-time signal. 通过抽样，将连续时间信号转换为离散时间信号，再使用离散时间系统来处理离散时间信号，然后将其转换回连续时间信号。,Specialized English for Communication Engineering,Sampling theorem can be stated as follows: Let x(t) be a band-limited signal with X(j)=0 for |m. Then x(t) is uniq
16、uely determined by its samples x(nT), n=0, 1, 2, , ifs2m where s=2/Tband-limited signal:频带有限的（低通）信号 is uniquely determined：被唯一地确定 抽样定理可以有下述关系表示：设x(t)是一个频带有限的（低通）信号，对于|m， X(j)=0 。若s2m ，其中 s=2/T，则x (t)可以被其抽样值x(nT)唯一地确定。,m：被抽样信号的最高频率,s ：抽样频率,T ：抽样间隔,Specialized English for Communication Engineering,Giv
17、en these samples, we can reconstruct x(t) by generating a periodic impulse train in which successive impulses have amplitudes that are successive sample values. impulse train ：脉冲序列 successive ： 连续的; 逐位的 已知这些样本值，我们可以用以下方法重构x(t)：产生一个周期的脉冲序列，其中连续脉冲的幅度等于依次而来的样本值。,Specialized English for Communication En
18、gineering,This impulse train is then processed through an ideal lowpass filter with gain T and cutoff frequency greater than m and less than s-m. The resulting output signal will exactly equal x (t) . ideal lowpass filter ：理想低通滤波器 gain ：增益 cutoff frequency：截止频率 然后将脉冲串通过一个增益为T，截止频率大于m，而小于s-m的理想低通滤波器，
19、产生的输出信号将精确的等于 x(t)。,Specialized English for Communication Engineering,The frequency 2m, which, under the sampling theorem, must be exceeded by the sampling frequency, is commonly referred to as the Nyquist rate. exceed：超过，超越的界限 successive ： 连续的; 逐位的 在抽样定理中，抽样频率必须超过2m ，通常将2m称作Nyquist 速率。,Specialized
20、English for Communication Engineering,In previous discussion, it was assumed that the sampling frequency was sufficiently high that the conditions of sampling theorem were met. sufficiently ：足够的，十分地, 充分地 在前面的讨论中，假设抽样频率足够高，因而满足抽样定理的条件。,Specialized English for Communication Engineering,As illustrated
21、in Fig.1, with s2m, the spectrum of the sampled signal consists of scaled replications of the spectrum of x(t), and this forms the basis for the sampling theorem. sampled signal ：取样（后的）信号 successive ： 连续的; 逐位的 如图1所示，若s2m,取样（后的）信号的频谱就是对原信号 x(t)频谱的复制, 这就构成了抽样定理的基础。,Specialized English for Communicatio
22、n Engineering,When s2m, X (j), the spectrum of x(t), is no longer replicated in Xp(j) and thus is no longer recoverable by lowpass filtering. The reconstructed signal will no longer be equal to x(t). This effect is referred to as aliasing. aliasing ：频谱折叠，混淆 当s2m时， x(t)的频谱X (j), 不再被Xp(j)所复制，也无法由低通滤波器
23、恢复。重建的信号也不再等于x(t)。这种结果称作频谱折叠（混淆）。,Specialized English for Communication Engineering,Sapling has a number of important applications. One particularly significant set of applications relates to using sampling to process continuous-time signals with discrete-time systems, by means of minicomputers, mic
24、roprocessors, or any of a variety of devices specifically oriented towards discrete-time signal processing. significant ：有意义的, 重要的 relate to ：涉及 minicomputer：小型计算机 microprocessor：微处理器 抽样有许多重要的应用。一些极其重要的应用涉及到通过抽样，用离散时间系统可以处理连续时间信号，这主要是依靠小型计算机、微处理器，或者任何用于离散时间信号处理的各种装置。,Specialized English for Communic
25、ation Engineering,Sapling has a number of important applications. One particularly significant set of applications relates to using sampling to process continuous-time signals with discrete-time systems, by means of minicomputers, microprocessors, or any of a variety of devices specifically oriented towards discrete-time signal processing. impulse train ：脉冲序列 successive ： 连续的; 逐位的 已知这些样本值，我们可以用以下方法重构x(t)：产生一个周期的脉冲序列，其中连续脉冲的幅度等于依次而来的样本值。,小 结,被动语态及其译法 The Sampling Theorem,
