OFDM基础--外文资料翻译(可编辑)

OFDM基础--外文资料翻译

附录A 外文资料

OFDM Basics

INTRODUCTION

The basic principle of OFDM is to split a high-rate data stream into a number of lower

rate streams that are transmitted simultaneously over a number of subcarriers. Because the symbol duration increases for the lower rate parallel subcarriers, the relative amount of dispersion in time caused by multipath delay spread is decreased. Inter symbol interference is eliminated almost completely by introducing a guard time in every OFDM symbol. In the guard time, the OFDM symbol is cyclically extended to avoid inter carrier interference In OFDM system design, a number of parameters are up for consideration, such as the number of subcarriers, guard time, symbol duration, subcarrier spacing,modulation type per subcarrier, and the type of forward error correction coding. The choice of parameters is influenced by system requirements such as available bandwidth,required bit rate, tolerable delay spread, and Doppler values. Some requirements are conflicting. For instance, to get a good delay spread tolerance, a large number of subcarriers with a small subcarrier

spacing is desirable, but the opposite is true for a good tolerance against Doppler spread and phase noiseGENERATION OF SUBCARRIERS USING THE IFFT An OFDM signal consists of a sum of subcarriers that are modulated by using phase shift keying PSK or quadrature amplitude modulation QAM.If di are the complex QAM symbols, N is the number of subcarriers, T is the symbol duration, and f is the carrier frequency, then one OFDM symbol starting at t t, can be written as2.1

In the literature, often the equivalent complex baseband notation is used, which is given by 2.2. In this representation, the real and imaginary parts correspond to the in-phase and quadrature parts of the OFDM signal, which have to be multiplied by a cosine and sine of the desired carrier frequency to produce the final OFDM signal.Figure 2.1 shows the operation of the OFDM modulator in a block diagram.

2.2 Figure 2.1 OFDM modulator

As an example,Figure2.2 shows four subcarriers from one OFDM signal. In this example, all subcarriers have the same phase and amplitude, but in practice the amplitudes and phases may be modulated differently for each subcarrier. Note that each subcarrier has exactly an integer number of cycles in the interval T, and the number of cycles between adjacent subcarriers differs by exactly one. This property accounts forthe orthogonality between the subcarriers. For instance, if the jth subcarrier from 2.2 is demodulated by down converting the signal with a

frequency of j/T and then integrating the signal over T seconds, the result is as written in 2.3. By looking at the intermediate result, it can be seen that a complex carrier is integrated over T seconds.For the demodulated subcarrier j, this integration gives the desired output multiplied by a constant factor T, which is the QAM value for that particular subcarrier. For all other subcarriers, the integration is zero, because the frequency difference produces an integer number of cycles within the integration interval T,such that the integration result is always zero.

2.3

The orthogonality of the different OFDM subcarriers can also be demonstrated in another way. According to 2.1, each OFDM symbol contains subcarriers that are nonzero over a T-second interval. Hence, the spectrum of a single symbol is a convolution of a group of Dirac pulses located at the subcarrier frequencies with the spectrum of a square pulse that is one for a T-second period and zero otherwise. The amplitude spectrum of the square pulse is equal to sincnJT, which has zeros for all frequencies f that are an integer multiple of 1IT. This effect is shown in Figure 2.2,which shows the overlapping sinc spectra of individual subcarriers. At the imum of each subcarrier spectrum, all other subcarrier spectra are zero. Because an OFDM receiver essentially calculates the

spectrum values at those points that correspond to the ima of individual subcarriers, it can demodulate each subcarrier free from any interference from the other subcarriers. Basically, Figure 2.3 shows that the OFDM spectrum fulfills Nyquist's criterium for an intersymbol interference free pulse shape.Notice that the pulse shape is present in the frequency domain

and not in the time domain, for which the Nyquist criterium usually is applied. Therefore, instead of intersymbol interference ISI, it is intercarrier interference ICI that is avoided by havingthe imum of one subcarrier spectrum correspond to zero crossings of all the others.

Figure 2.2 Example of four subcarriers within one OFDM symbol

The complex baseband OFDM signal as defined by 2.2 is in fact nothing more than the inverse Fourier transform of N, QAM input symbols. The time discrete equivalent is the inverse discrete Fourier transform IDFT, which is given by 2.4,where the time t is replaced by a sample number n. In practice, this transform can be implemented very efficiently by the inverse fast Fourier transform IFFT. An N point IDFT requires a total of N~ complex multiplications-which are actually only phase rotations. Of course, there are also additions necessary to do an IDFT, but since the hardware complexity of an adder is significantly lower than that of a multiplier or phase rotator, only the multiplications are used here for

comparison. The IFFT drastically reduces the amount of calculations by exploiting the regularity of the operations in the IDFT. Using the radix-2 algorithm, an N-point IFFT requires only N/2.log2N complex multiplications [I]. For a 16-point transform, for instance, the difference is 256 multiplications for the IDFT versus 32 for the IFFT-a reduction by a factor of 8!This difference grows for larger numbers of subcarriers, as the IDFT complexity grows quadratically with N, while the IFFT complexity only grows slightly faster than linear.

2.4

The number of multiplications in the JFFT can be reduced even further by using a radix-4 algorithm. This technique makes use of the fact that in a four-point IFFT,there are only multiplications by 1,-1 j,-j, which actually do not need to be implemented by a full multiplier, but rather by a simple add or subtract and a switch of real and imaginary parts in the case of multiplications by j or -j. In the radix-4 algorithm, the transform is split into a number of these trivial four-point transforms,and non-trivial multiplications only have to be performed between stages of these four-point transforms. In this way, an N-point FFT using the radix4 algorithm requires only 3/8Nlog2N-2 complex multiplications or phase rotations and Mog2N complex additions [I]GUARD TIME AND CYCLIC EXTENSION

One of the most important reasons to do OFDM is the efficient way it deals with multipath delay spread. By dividing the input datastream in Ns subcarriers, the symbol duration is made Ns times smaller, which also reduces the relative multipath delay spread, relative to the symbol time; by the same factor. To eliminate intersymbol interference almost completely, a guard time is introduced for each OFDM symbol. The guard time is chosen larger than the expected delay spread, such that multipath components from one symbol cannot interfere with the next symbol. The guard time could consist of no signal at all. In that case, however, the problem of intercarrier interference ICI would arise. ICI is crosstalk between different subcarriers, which means they are no longer orthogonal. This effect is illustrated in Figure 2.6. In this example, a subcarrier 1 and a delayed subcarrier 2 are shown. When an OFDM receivertries to demodulate the first subcarrier, it will encounter some interference from the second subcarrier, because within the FFT interval, there is no integer number of cycles difference between subcarrier 1 and 2. At the same time, there will be crosstalk from the first to the second subcarrier for the same reason.

Figure 2.6 Effect of multipath with zero signal in the guard time; the delayed subcarrier 2 causes ICI on subcarrier 1 and vice versa.

CHOICE OF OFDM PARAMETERS

The choice of various OFDM parameters is a trade off between various, often conflicting requirements. Usually, there are three main requirements to start with:bandwidth, bit rate, and delay spread. The delay spread directly dictates the guard time.As a rule, the guard time should be about two to four times the root-mean-squared delay spread. This value depends on the type of coding and QAM modulation. Higher order QAM like 64-QAM is more sensitive to ICI and IS1 than QPSK, while heavier coding obviously reduces the sensitivity to such interference.

Now that the guard time has been set, the symbol duration can be fixed. To minimize the signal-to-noise ratio SNR loss caused by the guard time, it is desirable to have the symbol duration much larger than the guard time. It cannot be arbitrarily large, however, because a larger symbol duration means more subcarriers with a smaller subcarrier spacing, a larger implementation complexity, and more sensitivity to phase noise and frequency offset [2], as well as an increased peak-to-average power ratio [3,4]. Hence, a practical design choice is to make the symbol duration at least five times the guard time, which implies a 1-dB SNR loss because of the guard time.

Form:OFDM for Wireless Multimedia Communications

OFDM基础

介绍

OFDM的基本原理是将一串高速数据流变成同时传输在一些副载波的低

速率数据流。由于低速率平行的副载波是符号持续时间增加,因而对多径效应引起的时延扩展有较强的抵抗力。符号间干扰可以通过在每个OFDM符号前引入一个保护间隔来完全消除。加入保护间隔后,OFDM符号通过周期性扩展来避免载波间干扰。

在OFDM系统设计中,大量的参数需要考虑,比如副载波的数量,保护间隔,持续时间,副载波间距,每一个副载波的调制类型,前项纠错编码的类型,参数的选择是受系统要求的如,可用带宽,需要的比特率,可容忍的延时时间和多普勒扩散值。但是有些要求是相互矛盾的。例如,为了得到一个好的延迟扩展公差,大部分副载波用一个小副载波的间距是可取的,但事实恰恰相反,一个好的公差不利于多普勒扩散和相位噪声。

用IFFT方法调制副载波

一个OFDM信号是利用相移键控调制相移键控或正交振幅调制组成的副载波之和,如果di是合成的QAM符号,N是子载波的数量,T是符号周期,f是载波频率,则一个OFDM符号从时刻开始,可以写成(2.1)

在文献中,等效的基带符号经常被写成式 2.2。在这个式子中,实部与虚部分别对应于OFDM信号的同相与正交部分,需要乘以一个余弦和正弦所需的载波频率生成最终的OFDM信号。图2.1表示了OFDM调制器的运算框图。

2.2

图2.1 OFDM调制

举个例子来说,在图2.2中,显示了4个子载波的实例,在这个例子中,所有子载波都有相同的相位和振幅,但实际中,每个子载波调制振幅与相位可能不

同。需要注意的是,每个子载波正好有一个整数数量的周期间隔T,周期数相邻的子载波刚好有一个不同。这个属性正好符合子载波之间的正交性方案。例如,假设式2.2的第j个子载波是通过频率的j / T将信号解调下来的,然后将信号在T秒内积分,结果就可以用式2.3表示。通过查看这个结果,可以看出,一个复杂的载体在T秒内积分。对于解调的子载波j,这种积分提供了所需的输出乘以一个常数因子T,这种特定的子载波就是QAM的优点。对于所有其他的子载波,积分是零,因为频率差异在积分间隔T内产生了一个整数的周期数,所以积分结果总是零。 2.3

图2.2 一个OFDM信号的四个子载波例子

OFDM的不同子载波的正交性可以用另一种方法表示。根据式 2.1,每个OFDM符号在其周期T内包括多个非零的子载波。因此其频谱可以看作是周期为T 的矩形脉冲的频谱与一组位于各个子载波频率上的单位冲激函数的卷积。矩形脉冲的频谱幅值为函数,这种函数的零点出现在频率为1/T整数倍的位置上。这种现象可以参见图 2.2,图中给出了相互覆盖的各个子信道内经过矩形波形成型得到的符号的函数频谱。在每个子载波频率最大值处,所有其他子信道的频谱值恰好为零。由于在对OFDM符号进行解调的过程中,需要计算这些点上所对应的每个子载波频率的最大值,因此可以从多个相互重叠的子信道符号中提取每一个信道符号,而不会受到其它子信道的干扰。图2.3基本上就可以显示OFDM满足奈奎斯特的标准,即多个子信道频谱之间不存在相互干扰。需要注意的是,脉冲形状出现在频域而不是时域,但是奈奎斯特标准也是适用的。因此这种一个子信道频谱出现最大值而其它子信道频谱为零的特点可以避免载波间干扰(ICI),而不是符号间干扰(ISI)。

对于输入QAM信号N比较大的系统来说,式2.2中的OFDM等效基带信号可以采用傅立叶逆变换来实现。时间离散等效于逆离散傅里叶变换IDFT,它用式2.4表示,其中的时间t替换为采样数n。然而在实际中,这种变换可以用非常有效的快速傅里叶逆变换来实现。一个N点IDFT需要共次复杂的乘法,但实际上只是相位旋转。当然,由于系统的需要,有必要增加IDFT点数,但是硬件复杂度一个加法器是明显低于一个乘数或相位旋转,这里只用复数乘法的运算量来比较。IFFT利用的规律性操作IDFT使计算量大大降低了。对于常用的基2 IFFT 算法来说,其复数乘法的次数仅为。对于一个涵盖面很广的16点变换,例如,不同的是IDFT需要256次乘法和而IFFT只需要32次乘法,是IDFT的,这种差异对于大量的子载波来说,IDFT的计算复杂度会随N的增加而呈现二次方增长,IFFT的计算复杂度的增加速度只是稍稍快于线性变化。

2.4

对于子载波数量非常大的OFDM系统来说,可以进一步采用基4 IFFT算法。在4点的IFFT运算中,只存在与1,-1,j,-j的相乘运算,这实际上不需要采用完整的乘法器来实施这种乘法,而是只需要通过简单的加、减以及交换实部和虚部的运算(当与-j,j相乘时)来实现这种乘法。在基4算法中,IFFT变换可以被分为多个4点的IFFT变换,这样就只需要在两个级别之间执行完整的乘法操作。一个N点的基4 IFFT使用算法中只需要执行次复数乘法或相位旋转,以及次复数加法。

保护间隔和循环扩展

应用OFDM的一个最重要是它可以有效的对抗多路延迟传播。通过把输入

数据流串并变换到Ns个并行的子信道中,符号持续时间较小,相对于符号时间这也相对降低了多路延迟传播的时间,为了最大限度的消除符号间干扰,还可以在每个OFDM符号间插入保护间隔。而且该保护间隔长度一般要大于无线信道中的最大时延扩展,这样一个符号的多径分量就不会对下一个符号造成干扰。在这段保护间隔内,可以不插入任何信号,即是一段空闲的传输时段,然而,在这种情况下,载波间干扰的问题ICI将会出现。即子载波之间的正交性遭到破坏,不同的子载波之间产生干扰,这种效果如图2.6。在这个例子中,给出了第一子载波和第二子载波的时延信号。由于在FFT运算时间长度内,第一子载波与带有时延的第二子载波之间的周期个数只差不再是整数,所以当接收机试图对第一子载波进行解调时,第二子载波会对此造成干扰。同时,当接收机对第二子载波进行解调时,也会来自第一子载波的干扰。

OFDM的参数选择

选择各种OFDM的参数是需要权衡各种相互冲突。通常,有3个主要的参数:带宽、比特率、保护间隔。延迟传播直接决定了保护间隔。一般来说,保护间隔的时间长度应该为应用移动环境信道的时延均方根值的2~4倍。这个值取决于编码类型和QAM调制。高阶QAM如64-QAM对ICI和ISI比QPSK更为敏感,而译码明显减少这种干扰的敏感性。

一旦确定了保护间隔,则OFDM符号周期长度就可以确定。为了最大限度的减少由于插入保护间隔所带来的信噪比的损失,理论上需要OFDM符号周期长度可以远远大于保护间隔长度。但是符号周期长度又不可能任意大,否则OFDM 系统中包括更多的子载波数,从而导致子载波间隔相应减少,系统的实现复杂度增加,而且还加大了系统的峰值平均功率比,同时使系统对频率偏差更加敏感。因

此在实际应用中,一般选择符号周期是保护间隔长度的5倍,这样由于插入保护比特所造成的信噪比损耗只有1dB左右。

源于:OFDM系统的无线多媒体通信

英文论文及中文翻译

International Journal of Minerals, Metallurgy and Materials Volume 17, Number 4, August 2010, Page 500 DOI: 10.1007/s12613-010-0348-y Corresponding author: Zhuan Li E-mail: li_zhuan@https://www.wendangku.net/doc/8516975685.html, ? University of Science and Technology Beijing and Springer-Verlag Berlin Heidelberg 2010 Preparation and properties of C/C-SiC brake composites fabricated by warm compacted-in situ reaction Zhuan Li, Peng Xiao, and Xiang Xiong State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083, China (Received: 12 August 2009; revised: 28 August 2009; accepted: 2 September 2009) Abstract: Carbon fibre reinforced carbon and silicon carbide dual matrix composites (C/C-SiC) were fabricated by the warm compacted-in situ reaction. The microstructure, mechanical properties, tribological properties, and wear mechanism of C/C-SiC composites at different brake speeds were investigated. The results indicate that the composites are composed of 58wt% C, 37wt% SiC, and 5wt% Si. The density and open porosity are 2.0 g·cm–3 and 10%, respectively. The C/C-SiC brake composites exhibit good mechanical properties. The flexural strength can reach up to 160 MPa, and the impact strength can reach 2.5 kJ·m–2. The C/C-SiC brake composites show excellent tribological performances. The friction coefficient is between 0.57 and 0.67 at the brake speeds from 8 to 24 m·s?1. The brake is stable, and the wear rate is less than 2.02×10?6 cm3·J?1. These results show that the C/C-SiC brake composites are the promising candidates for advanced brake and clutch systems. Keywords: C/C-SiC; ceramic matrix composites; tribological properties; microstructure [This work was financially supported by the National High-Tech Research and Development Program of China (No.2006AA03Z560) and the Graduate Degree Thesis Innovation Foundation of Central South University (No.2008yb019).] 温压-原位反应法制备C / C-SiC刹车复合材料的工艺和性能 李专，肖鹏，熊翔 粉末冶金国家重点实验室，中南大学，湖南长沙410083，中国（收稿日期：2009年8月12日修订：2009年8月28日;接受日期：2009年9月2日） 摘要：采用温压?原位反应法制备炭纤维增强炭和碳化硅双基体(C/C-SiC)复合材

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五、外文资料翻译 Stress and Strain 1.Introduction to Mechanics of Materials Mechanics of materials is a branch of applied mechanics that deals with the behavior of solid bodies subjected to various types of loading. It is a field of study that i s known by a variety of names, including “strength of materials” and “mechanics of deformable bodies”. The solid bodies considered in this book include axially-loaded bars, shafts, beams, and columns, as well as structures that are assemblies of these components. Usually the objective of our analysis will be the determination of the stresses, strains, and deformations produced by the loads; if these quantities can be found for all values of load up to the failure load, then we will have obtained a complete picture of the mechanics behavior of the body. Theoretical analyses and experimental results have equally important roles in the study of mechanics of materials . On many occasion we will make logical derivations to obtain formulas and equations for predicting mechanics behavior, but at the same time we must recognize that these formulas cannot be used in a realistic way unless certain properties of the been made in the laboratory. Also , many problems of importance in engineering cannot be handled efficiently by theoretical means, and experimental measurements become a practical necessity. The historical development of mechanics of materials is a fascinating blend of both theory and experiment, with experiments pointing the way to useful results in some instances and with theory doing so in others①. Such famous men as Leonardo da Vinci(1452-1519) and Galileo Galilei (1564-1642) made experiments to adequate to determine the strength of wires , bars , and beams , although they did not develop any adequate theo ries (by today’s standards ) to explain their test results . By contrast , the famous mathematician Leonhard Euler(1707-1783) developed the mathematical theory any of columns and calculated the critical load of a column in 1744 , long before any experimental evidence existed to show the significance of his results ②. Thus , Euler’s theoretical results remained unused for many years, although today they form the basis of column theory. The importance of combining theoretical derivations with experimentally determined properties of materials will be evident theoretical derivations with experimentally determined properties of materials will be evident as we proceed with

外文翻译

Load and Ultimate Moment of Prestressed Concrete Action Under Overload-Cracking Load It has been shown that a variation in the external load acting on a prestressed beam results in a change in the location of the pressure line for beams in the elastic range.This is a fundamental principle of prestressed construction.In a normal prestressed beam,this shift in the location of the pressure line continues at a relatively uniform rate,as the external load is increased,to the point where cracks develop in the tension fiber.After the cracking load has been exceeded,the rate of movement in the pressure line decreases as additional load is applied,and a significant increase in the stress in the prestressing tendon and the resultant concrete force begins to take place.This change in the action of the internal moment continues until all movement of the pressure line ceases.The moment caused by loads that are applied thereafter is offset entirely by a corresponding and proportional change in the internal forces,just as in reinforced-concrete construction.This fact,that the load in the elastic range and the plastic range is carried by actions that are fundamentally different,is very significant and renders strength computations essential for all designs in order to ensure that adequate safety factors exist.This is true even though the stresses in the elastic range may conform to a recognized elastic design criterion. It should be noted that the load deflection curve is close to a straight line up to the cracking load and that the curve becomes progressively more curved as the load is increased above the cracking load.The curvature of the load-deflection curve for loads over the cracking load is due to the change in the basic internal resisting moment action that counteracts the applied loads,as described above,as well as to plastic strains that begin to take place in the steel and the concrete when stressed to high levels. In some structures it may be essential that the flexural members remain crack free even under significant overloads.This may be due to the structures’being exposed to exceptionally corrosive atmospheres during their useful life.In designing prestressed members to be used in special structures of this type,it may be necessary to compute the load that causes cracking of the tensile flange,in order to ensure that adequate safety against cracking is provided by the design.The computation of the moment that will cause cracking is also necessary to ensure compliance with some design criteria. Many tests have demonstrated that the load-deflection curves of prestressed beams are approximately linear up to and slightly in excess of the load that causes the first cracks in the tensile flange.(The linearity is a function of the rate at which the load is applied.)For this reason,normal elastic-design relationships can be used in computing the cracking load by simply determining the load that results in a net tensile stress in the tensile flange(prestress minus the effects of the applied loads)that is equal to the tensile strength of the concrete.It is customary to assume that the flexural tensile strength of the concrete is equal to the modulus of rupture of the

英文文献及中文翻译

毕业设计说明书 英文文献及中文翻译 学院：专 2011年6月 电子与计算机科学技术软件工程

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土木外文翻译原文和译文

A convection-conduction model for analysis of the freeze-thaw conditions in the surrounding rock wall of a tunnel in permafrost regions Abstract Based on the analyses of fundamental meteorological and hydrogeological conditions at the site of a tunnel in the cold regions, a combined convection-conduction model for air flow in the tunnel and temperature field in the surrounding has been constructed. Using the model, the air temperature distribution in the Xiluoqi No. 2 Tunnel has been simulated numerically. The simulated results are in agreement with the data observed. Then, based on the in situ conditions of sir temperature, atmospheric pressure, wind force, hydrogeology and engineering geology, the air-temperature relationship between the temperature on the surface of the tunnel wall and the air temperature at the entry and exit of the tunnel has been obtained, and the freeze-thaw conditions at the Dabanshan Tunnel which is now under construction is predicted. Keywords: tunnel in cold regions, convective heat exchange and conduction, freeze-thaw. A number of highway and railway tunnels have been constructed in the permafrost regions and their neighboring areas in China. Since the hydrological and thermal conditions changed after a tunnel was excavated，the surrounding wall rock materials often froze, the frost heaving caused damage to the liner layers and seeping water froze into ice diamonds，which seriously interfered with the communication and transportation. Similar problems of the freezing damage in the tunnels also appeared in other countries like Russia, Norway and Japan .Hence it is urgent to predict the freeze-thaw conditions in the surrounding rock materials and provide a basis for the design，construction and

平面设计中英文对照外文翻译文献

(文档含英文原文和中文翻译) 中英文翻译 平面设计 任何时期平面设计可以参照一些艺术和专业学科侧重于视觉传达和介绍。采用多种方式相结合，创造和符号，图像和语句创建一个代表性的想法和信息。平面设计师可以使用印刷，视觉艺术和排版技术产生的最终结果。平面设计常常提到的进程，其中沟通是创造和产品设计。 共同使用的平面设计包括杂志，广告，产品包装和网页设计。例如，可能包括产品包装的标志或其他艺术作品，举办文字和纯粹的设计元素，如形状和颜色统一件。组成的一个最重要的特点，尤其是平面设计在使用前现有材料或不同的元素。 平面设计涵盖了人类历史上诸多领域，在此漫长的历史和在相对最近爆炸视觉传达中的第20和21世纪，人们有时是模糊的区别和重叠的广告艺术，平面设计和美术。毕竟，他们有着许多相同的内容，理论，原则，做法和语言，有时同样的客人或客户。广告艺术的最终目标是出售的商品和服务。在平面

设计，“其实质是使以信息，形成以思想，言论和感觉的经验”。 在唐朝（ 618-906 ）之间的第4和第7世纪的木块被切断打印纺织品和后重现佛典。阿藏印在868是已知最早的印刷书籍。 在19世纪后期欧洲，尤其是在英国，平面设计开始以独立的运动从美术中分离出来。蒙德里安称为父亲的图形设计。他是一个很好的艺术家，但是他在现代广告中利用现代电网系统在广告、印刷和网络布局网格。 于1849年，在大不列颠亨利科尔成为的主要力量之一在设计教育界，该国政府通告设计在杂志设计和制造的重要性。他组织了大型的展览作为庆祝现代工业技术和维多利亚式的设计。 从1892年至1896年威廉?莫里斯凯尔姆斯科特出版社出版的书籍的一些最重要的平面设计产品和工艺美术运动，并提出了一个非常赚钱的商机就是出版伟大文本论的图书并以高价出售给富人。莫里斯证明了市场的存在使平面设计在他们自己拥有的权利，并帮助开拓者从生产和美术分离设计。这历史相对论是，然而，重要的，因为它为第一次重大的反应对于十九世纪的陈旧的平面设计。莫里斯的工作，以及与其他私营新闻运动，直接影响新艺术风格和间接负责20世纪初非专业性平面设计的事态发展。 谁创造了最初的“平面设计”似乎存在争议。这被归因于英国的设计师和大学教授Richard Guyatt，但另一消息来源于20世纪初美国图书设计师William Addison Dwiggins。 伦敦地铁的标志设计是爱德华约翰斯顿于1916年设计的一个经典的现代而且使用了系统字体设计。 在20世纪20年代，苏联的建构主义应用于“智能生产”在不同领域的生产。个性化的运动艺术在俄罗斯大革命是没有价值的，从而走向以创造物体的功利为目的。他们设计的建筑、剧院集、海报、面料、服装、家具、徽标、菜单等。 Jan Tschichold 在他的1928年书中编纂了新的现代印刷原则，他后来否认他在这本书的法西斯主义哲学主张，但它仍然是非常有影响力。 Tschichold ，包豪斯印刷专家如赫伯特拜耳和拉斯洛莫霍伊一纳吉，和El Lissitzky 是平面设计之父都被我们今天所知。 他们首创的生产技术和文体设备，主要用于整个二十世纪。随后的几年看到平面设计在现代风格获得广泛的接受和应用。第二次世界大战结束后，美国经济的建立更需要平面设计，主要是广告和包装等。移居国外的德国包豪斯设计学院于1937年到芝加哥带来了“大规模生产”极简到美国;引发野火的“现代”建筑和设计。值得注意的名称世纪中叶现代设计包括阿德里安Frutiger ，设计师和Frutiger字体大学;保兰德，从20世纪30年代后期，直到他去世于1996年，采取的原则和适用包豪斯他们受欢迎的广告和标志设计，帮助创造一个独特的办法，美国的欧洲简约而成为一个主要的先驱。平面设计称为企业形象;约瑟夫米勒，罗克曼，设计的海报严重尚未获取1950年代和1960年代时代典型。 从道路标志到技术图表，从备忘录到参考手册，增强了平面设计的知识转让。可读性增强了文字的视觉效果。 设计还可以通过理念或有效的视觉传播帮助销售产品。将它应用到产品和公司识别系统的要素像标志、颜色和文字。连同这些被定义为品牌。品牌已日益成为重要的提供的服务范围，许多平面设计师，企业形象和条件往往是同时交替使用。

10kV小区供配电英文文献及中文翻译

在广州甚至广东的住宅小区电气设计中,一般都会涉及到小区的高低压供配电系统的设计.如10kV高压配电系统图,低压配电系统图等等图纸一大堆.然而在真正实施过程中,供电部门(尤其是供电公司指定的所谓电力设计小公司)根本将这些图纸作为一回事,按其电脑里原有的电子档图纸将数据稍作改动以及断路器按其所好换个厂家名称便美其名曰设计(可笑不?),拿出来的图纸根本无法满足电气设计的设计意图,致使严重存在以下问题:(也不知道是职业道德问题还是根本一窍不通) 1.跟原设计的电气系统货不对板,存在与低压开关柜后出线回路严重冲突,对实际施工造成严重阻碍,经常要求设计单位改动原有电气系统图才能满足它的要求(垄断的没话说). 2.对消防负荷和非消防负荷的供电(主要在高层建筑里)应严格分回路(从母线段)都不清楚,将消防负荷和非消防负荷按一个回路出线(尤其是将电梯和消防电梯,地下室的动力合在一起等等,有的甚至将楼顶消防风机和梯间照明合在一个回路,以一个表计量). 3.系统接地保护接地型式由原设计的TN-S系统竟曲解成"TN-S-C-S"系统(室内的还需要做TN-C,好玩吧?),严格的按照所谓的"三相四线制"再做重复接地来实施,导致后续施工中存在重复浪费资源以及安全隐患等等问题.. ............................(违反建筑电气设计规范等等问题实在不好意思一一例举,给那帮人留点混饭吃的面子算了) 总之吧,在通过图纸审查后的电气设计图纸在这帮人的眼里根本不知何物,经常是完工后的高低压供配电系统已是面目全非了,能有百分之五十的保留已经是谢天谢地了. 所以.我觉得:住宅建筑电气设计,让供电部门走!大不了留点位置,让他供几个必需回路的电,爱怎么折腾让他自个怎么折腾去.. Guangzhou, Guangdong, even in the electrical design of residential quarters, generally involving high-low cell power supply system design. 10kV power distribution systems, such as maps, drawings, etc. low-voltage distribution system map a lot. But in the real implementation of the process, the power sector (especially the so-called power supply design company appointed a small company) did these drawings for one thing, according to computer drawings of the original electronic file data to make a little change, and circuit breakers by their the name of another manufacturer will be sounding good design (ridiculously?), drawing out the design simply can not meet the electrical design intent, resulting in a serious following problems: (do not know or not know nothing about ethical issues) 1. With the original design of the electrical system not meeting board, the existence and low voltage switchgear circuit after qualifying serious conflicts seriously hinder the actual construction, often require changes to the original design unit plans to meet its electrical system requirements (monopoly impress ). 2. On the fire load and fire load of non-supply (mainly in high-rise building in) should be strictly sub-loop (from the bus segment) are not clear, the fire load and fire load of non-qualifying press of a circuit (especially the elevator and fire elevator, basement, etc.

毕业设计外文翻译资料

外文出处： 《Exploiting Software How to Break Code》By Greg Hoglund, Gary McGraw Publisher : Addison Wesley Pub Date : February 17, 2004 ISBN : 0-201-78695-8 译文标题： JDBC接口技术 译文： JDBC是一种可用于执行SQL语句的JavaAPI（ApplicationProgrammingInterface应用程序设计接口）。它由一些Java语言编写的类和界面组成。JDBC为数据库应用开发人员、数据库前台工具开发人员提供了一种标准的应用程序设计接口，使开发人员可以用纯Java语言编写完整的数据库应用程序。 一、ODBC到JDBC的发展历程 说到JDBC，很容易让人联想到另一个十分熟悉的字眼“ODBC”。它们之间有没有联系呢？如果有，那么它们之间又是怎样的关系呢？ ODBC是OpenDatabaseConnectivity的英文简写。它是一种用来在相关或不相关的数据库管理系统（DBMS）中存取数据的，用C语言实现的，标准应用程序数据接口。通过ODBCAPI，应用程序可以存取保存在多种不同数据库管理系统（DBMS）中的数据，而不论每个DBMS使用了何种数据存储格式和编程接口。 1．ODBC的结构模型 ODBC的结构包括四个主要部分：应用程序接口、驱动器管理器、数据库驱动器和数据源。应用程序接口：屏蔽不同的ODBC数据库驱动器之间函数调用的差别，为用户提供统一的SQL编程接口。 驱动器管理器：为应用程序装载数据库驱动器。 数据库驱动器：实现ODBC的函数调用，提供对特定数据源的SQL请求。如果需要，数据库驱动器将修改应用程序的请求，使得请求符合相关的DBMS所支持的文法。 数据源：由用户想要存取的数据以及与它相关的操作系统、DBMS和用于访问DBMS的网络平台组成。 虽然ODBC驱动器管理器的主要目的是加载数据库驱动器，以便ODBC函数调用，但是数据库驱动器本身也执行ODBC函数调用，并与数据库相互配合。因此当应用系统发出调用与数据源进行连接时，数据库驱动器能管理通信协议。当建立起与数据源的连接时，数据库驱动器便能处理应用系统向DBMS发出的请求，对分析或发自数据源的设计进行必要的翻译，并将结果返回给应用系统。 2．JDBC的诞生 自从Java语言于1995年5月正式公布以来，Java风靡全球。出现大量的用java语言编写的程序，其中也包括数据库应用程序。由于没有一个Java语言的API，编程人员不得不在Java程序中加入C语言的ODBC函数调用。这就使很多Java的优秀特性无法充分发挥，比如平台无关性、面向对象特性等。随着越来越多的编程人员对Java语言的日益喜爱，越来越多的公司在Java程序开发上投入的精力日益增加，对java语言接口的访问数据库的API 的要求越来越强烈。也由于ODBC的有其不足之处，比如它并不容易使用，没有面向对象的特性等等，SUN公司决定开发一Java语言为接口的数据库应用程序开发接口。在JDK1．x 版本中，JDBC只是一个可选部件，到了JDK1．1公布时，SQL类包（也就是JDBCAPI）

中文和英文简历和专业英语材料翻译

韶关学院 期末考核报告 科目：专业英语 学生姓名： 学号： 同组人： 院系： 专业班级： 考核时间：2012年10月9日—2012年11月1 日评阅教师： 评分：

第1章英文阅读材料翻译 (1) 第2章中文摘要翻译英文 (3) 第3章中文简历和英文简历 (4) 第4章课程学习体会和建议 (6) 参考文献 (7)

第1章英文阅读材料翻译 Mechanization and Automation Processes of mechanization have been developing and becoming more complex ever since the beginning of the Industrial Revolution at the end of the 18th century. The current developments of automatic processes are, however, different from the old ones. The “automation” of the 20th century is distinct from the mechanization of the 18th and 19th centuries inasmuch as mechanization was applied to individual operations, wherea s “automation” is concerned with the operation and control of a complete producing unit. And in many, though not all, instances the element of control is so great that whereas mechanization displaces muscle, “automation”displaces brain as well. The distinction between the mechanization of the past and what is happening now is, however, not a sharp one. At one extreme we have the electronic computer with its quite remarkable capacity for discrimination and control, while at the other end of the scale are “ transfer machines” , as they are now called, which may be as simple as a conveyor belt to another. An automatic mechanism is one which has a capacity for self-regulation; that is, it can regulate or control the system or process without the need for constant human attention or adjustment. Now people often talk about “feedback” as begin an essential factor of the new industrial techniques, upon which is base an automatic self-regulating system and by virtue of which any deviation in the system from desired condition can be detected, measured, reported and corrected. when “feedback” is applied to the process by which a large digital computer runs at the immense speed through a long series of sums, constantly rejecting the answers until it finds one to fit a complex set of facts which have been put to it, it is perhaps different in degree from what we have previously been accustomed to machines. But “feedback”, as such, is a familiar mechanical conception. The old-fashioned steam engine was fitted with a centrifugal governor, two balls on levers spinning round and round an upright shaft. If the steam pressure rose and the engine started to go too fast, the increased speed of the spinning governor caused it to rise up the vertical rod and shut down a valve. This cut off some of the steam and thus the engine brought itself back to its proper speed. The mechanization, which was introduced with the Industrial Revolution, because it was limited to individual processes, required the employment of human labor to control each machine as well as to load and unload materials and transfer them from one place to another. Only in a few instances were processes automatically linked together and was production organized as a continuous flow. In general, however, although modern industry has been highly mechanized ever since the 1920s, the mechanized parts have not as a rule been linked together. Electric-light bulbs, bottles and the components of innumerable mass-produced