【正文】 Nontraditional Machining Processes IntroductionTraditional or conventional machining, such as turning, milling, and grinding etc., uses mechanical energy to shear metal against another substance to create holes or remove machining processes are defined as a group of processes that remove excess material by various techniques involving mechanical, thermal, electrical or chemical energy or binations of these energies but do not use a sharp cutting tool as it is used in traditional manufacturing hard and brittle materials are difficult to be machined by traditional machining traditional methods to machine such materials means increased demand for time and energy and therefore increases in costs。這種加工過程不產(chǎn)生熱量、無化學(xué)反應(yīng)，加工出的零件在微結(jié)構(gòu)、化學(xué)和物理特性方面都不發(fā)生變化，可以獲得無應(yīng)力加工表面。激光打孔深度可以控制到每個激光脈沖不超過一微米，且可以根據(jù)加工要求很靈活地留下非常淺的永久性標(biāo)記。為了獲得電化學(xué)過程形狀復(fù)制的高精度和高的材料去除率，需要采用高的電流密度（范圍為10～100 A/cm2)和低電壓（范圍為8～30V）。由于蝕刻劑沿垂直和水平方向開始蝕除材料，鉆蝕（又稱為淘蝕）量進(jìn)一步加大。傳統(tǒng)加工工藝依靠硬質(zhì)刀具或磨料去除較軟的材料，而特種加工工藝如電火花加工，則是利用電火花或熱能來電蝕除余料，以獲得所需的零件形狀。由于這些曲線顯示，辦法，AWGN信道的一對L時，對MCSS系統(tǒng)性能有很大價值。或者，不同的多普勒譜定義在[8]個人頻道。對于多載波調(diào)制系統(tǒng)，子通道間距FS可以變得非常小，這樣可以造成嚴(yán)重的多普勒效應(yīng)ICI的。平均時延特性參數(shù)為有圖12時變信道沖激響應(yīng)和通道傳遞函數(shù)頻率選擇性衰落是權(quán)力頁的路徑均方根時延擴(kuò)展的定義為 同樣，多普勒頻譜的功率密度（FD）的特點(diǎn)可以定義在移動時變無線信道，并給出了作為一種金融衍生工具功能的多普勒頻率通道輸出的平均功率。Help yourself to the it while it’s live and die but life ，但生活仍在繼續(xù)。He will fall asleep as soon as his head touches the ，如果我們沒有足夠的勇氣，這個計劃將會徹底失敗。Whether the research team will acplish the task ro not, nobody really ，沒有人會真的知道。She wants to further her study abroad after do 。，慶祝我的生日。Some parents just buy whatever their children want.第二篇：中英文翻譯Fundamentals This chapter describes the fundamentals of today’s wireless a detailed description of the radio channel and its modeling are presented, followed by the introduction of the principle of OFDM multicarrier addition, a general overview of the spread spectrum technique, especially DSCDMA, is given and examples of potential applications for OFDM and DSCDMA are introduction is essential for a better understanding of the idea behind the bination of OFDM with the spread spectrum technique, which is briefly introduced in the last part of this Radio Channel Characteristics Understanding the characteristics of the munications medium is crucial for the appropriate selection of transmission system architecture, dimensioning of its ponents, and optimizing system parameters, especially since mobile radio channels are considered to be the most difficult channels, since they suffer from many imperfections like multipath fading, interference, Doppler shift, and choice of system ponents is totally different if, for instance, multipath propagation with long echoes dominates the radio , an accurate channel model describing the behavior of radio wave propagation in different environments such as mobile/fixed and indoor/outdoor is may allow one, through simulations, to estimate and validate the performance of a given transmission scheme in its several design Understanding Radio Channels In mobile radio channels(see Figure 11), the transmitted signal suffers from different effects, which are characterized as follows: Multipath propagation occurs as a consequence of reflections, scattering, and diffraction of the transmitted electromagnetic wave at natural and manmade , at the receiver antenna, a multitude of waves arrives from many different directions with different delays, attenuations, and superposition of these waves results in amplitude and phase variations of the posite received spread is caused by moving objects in the mobile radio in the phases and amplitudes of the arriving waves occur which lead to timevariant multipath small movements on the order of the wavelength may result in a totally different wave varying signal strength due to timevariant multipath propagation is referred to as fast is caused by obstruction of the transmitted waves by, ., hills, buildings, walls, and trees, which results in more or less strong attenuation of the signal to fast fading, longer distances have to be covered to significantly change the shadowing varying signal strength due to shadowing is called slow fading and can be described by a lognormal distribution [36].Path loss indicates how the mean signal power decays with distance between transmitter and free space, the mean signal power decreases with the square of the distance between base station(BS)and terminal station(TS).In a mobile radio channel, where often no line of sight(LOS)path exists, signal power decreases with a power higher than two and is typically in the order of three to of the received power due to shadowing and path loss can be efficiently counteracted by power the following, the mobile radio channel is described with respect to its fast fading Channel Modeling The mobile radio channel can be characterized by the timevariant channel impulse response h(τ , t)or by the timevariant channel transfer function H(f, t), which is the Fourier transform of h(τ , t).The channel impulse response represents the response of the channel at time t due to an impulse applied at time t ? mobile radio channel is assumed to be a widesense stationary random process, ., the channel has a fading statistic that remains constant over short periods of time or small spatial environments with multipath propagation, the channel impulse response is posed of a large number of scattered impulses received over Np different paths，Whereand ap, fD,p, ?p, and τp are the amplitude, the Doppler frequency, the phase, and the propagation delay, respectively, associated with path p, p = 0,..., Np ? assigned channel transfer function isThe delays are measured relative to the first detectable path at the Doppler Frequencydepends on the velocity v of the terminal station, the speed of light c, the carrier frequency fc, and the angle of incidence αp of a wave assigned to path channel impulse response with corresponding channel transfer function is illustrated in Figure delay power density spectrum