外文翻譯--底土的土壤結(jié)構(gòu)和飽和導(dǎo)水率

1、<p><b>　　英文原文：</b></p><p>　　Low-cost programmable pulse generator for particle telescope calibration</p><p><b>　　Abstract</b></p><p>　　In this paper we

2、present a new calibration system for particle telescopes including multi pulse generator and digital controller. The calibration system generates synchronized pulses of variable height for every detector channel on the t

3、elescope. The control system is based on a commercial microcontroller linked to a personal computer through an RS-232 bidirectional line. The aim of the device is to perform laboratory calibration of multi-detector teles

4、copes prior to calibration at accelerator. </p><p>　　To assure a correct interpretation of data obtained with scientific instruments onboard satellites, as well as to compare these data with those of similar

5、 instruments, a thorough pre-flight calibration is required. For solar and cosmic ray particle telescopes, this calibration is usually carried out in two steps: first, a calibration of each individual detector using radi

6、oactive sources and standard nuclear instrumentation (NIM or CAMAC modules),following by a final test of the whole telescope p</p><p>　　The standard calibration procedure for individual detectors and their e

7、lectronic chains consists of introducing pulses of known amplitudes coming from a pulse generator, together with the pulses released in the detector by particles coming from a radioactive source. However, these standard

8、pulse generators do present several limitations: The pulse amplitude must be set manually. Thus, to generate the pulses that different particles with different energies would release on the detectors, it is ne</p>

9、<p>　　Standard pulse generators only provide one output signal, so either several modules are needed to calibrate a complete telescope, or it is necessary to split the single output in order to get several signals.

10、 It is difficult to check the coincidence logic because the four signals are not independent.</p><p>　　To overcome these difficulties, pulse generators of programmable amplitude and rate have been proposed.

11、Abdel-Aal [1]presented a programmable random pulse generator where the height and separation of individual pulses are controlled by software.But in his scheme the pulses are released directly from a digital-to-analog con

12、verter(DAC),thus having the temporal characteristics of the DAC output. Our purpose is to generate variable height analog pulses with similar shape to that released by nuclear </p><p>　　The low-cost PPG pres

13、ented here is intended to introduce every detector channel ，the pulses released by any particle flux supposed to be encountered by the instrument on real experiments (in our case, on outer space environment). The propose

14、d pre-calibration scheme is sketched in the diagram of Fig 1. For a big number of simulated events, the energy signals released at the different detectors of the telescope are stored on a personal computer (PC). For each

15、 individual event, the energy signal da</p><p><b>　　Fig 1 </b></p><p>　　2 PPG description</p><p>　　The design of the PPG is divided into two functional modules: digita

16、l electronics and analog electronics, whose block diagrams are enclosed in dashed boxes shown in Fig2. The data arriving at the digital module from the PC are sent to 12 bit DAC. The DAC output voltages are transformed i

17、n the analog module into suitable pulses, ready to be introduced into the test input of the related detector channel of the telescope.</p><p>　　Analog and digital modules are described with some detail in Se

18、ctions 2.1 and 2.2. In Section 2.3 we describe some noise problems related with the microcontroller, and the way we found to solve them.</p><p>　　2.1 Analog module</p><p>　　This module must be

19、capable of producing signal pulses similar to those generated in the detectors by the passage of energetic charged particles, whose shape can be described by the following function:</p><p><b>　　(1)<

20、/b></p><p>　　The relevant signal parameters are the pulse height or amplitude A, the rise time and the fall time (here expressed as 1/e times rather than 10-90% times). Using semiconductor detectors, ty

21、pical values for and are approximately 5 ns and 10 us, respectively.</p><p>　　Our particular telescope has four detectors, therefore four almost simultaneous pulses with different amplitudes have to be gen

22、erated for each simulated event. These amplitudes are sent by the digital module to the analog module, together with a start pulse (see Fig 2). The communication is performed through a coupler circuit for isolation purpo

23、ses. The start signal is sent to a reference pulse generator, which generates a pulse of constant amplitude, rise and fall times. One of the inputs of ea</p><p>　　The reference pulse generator is the most cr

24、itical element in the system, because any noise in the reference pulse will be present (and not independently) in each of the output signals. The core of this element is the circuit shown in Fig 3. Before a start pulse a

25、rrives to the reference pulse generator, the capacitoris charged at voltage, ultra-precision, guaranteed long-term drift voltage reference has been used for this purpose (MAX677BCPP). Once the capacitor present stable v

26、oltage and a sta</p><p><b>　　(2)</b></p><p>　　The solution of this linear system with the conditions and gives an output pulse with the functional form (1) and amplitude. Though the

27、 rise and fall times depend on resistor and capacitor values through a complicated algebraic expression, for (condition fulfilled here) the following approximate expressions hold:</p><p><b>　　(3)</

28、b></p><p>　　The values and characteristics of capacitors, resistors and reference voltage are given in Table 1; for these values ns and . The shape, rise and fall time of the reference pulse are shown in

29、 Fig 4 .</p><p>　　Fig 4. Oscilloscope images of the reference pulse rise (left) and fall (right) flanges. The quoted values of rise and fall time refer to 10-90%of the amplitude. The values of and in the t

30、ext refer to 1/e of the amplitude.</p><p>　　The reference pulse generator must present very good time stability against temperature and power supply variations, as well as noise immunity. In order to meet th

31、ese restrictions, special components have been used, and the reference pulse generator has been placed inside a Faraday cup with the aim of isolating it from the rest of the system.</p><p>　　In order to resp

32、ond to the high-frequency components of the reference pulse (rise time~5 ns), the multiplier AD834, which presents 4 ns transition time, has been chosen. </p><p>　　The output range provided by the multiplier

33、s 0-1000 mV, and the output signals of every detector channel are digitized by 0-4096 bit ADC. Thus, every multiplier output must be adjusted to cover the corresponding ADC range. This requirement is fulfilled by suitabl

34、e pi attenuators, that match the PPG output and test input characteristic impedances, while adapting the output and input ranges. These attenuators can be easily changed to match any detector channel.</p><p>

35、;<b>　　中文翻譯：</b></p><p>　　底土的土壤結(jié)構(gòu)和飽和導(dǎo)水率</p><p><b>　　摘要</b></p><p>　　飽和導(dǎo)水率，是在從耕作層和底土中采集來(lái)的土壤樣品上衡量的。自然產(chǎn)生的土壤容重的范圍，是通過(guò)對(duì)不同年份有或沒(méi)有輪軌的不同作物取樣而得來(lái)的。據(jù)研究發(fā)現(xiàn)，對(duì)耕作層來(lái)說(shuō)，的對(duì)數(shù)與容重之間存

36、在著相當(dāng)好的線性關(guān)系。然而，對(duì)于底土，的價(jià)值通常在于能發(fā)現(xiàn)相應(yīng)耕作層的回歸線。底土的這種過(guò)度的導(dǎo)水率，是由于水力傳導(dǎo)的生物過(guò)程，尤其是源渠道的存在。耕作層較低的滲透系數(shù)，相對(duì)于底土，是由于這些生物過(guò)程被耕作破壞。已經(jīng)提出了一種簡(jiǎn)單的模型，在這種模型中，土壤質(zhì)地和渠道根源都分別有利于的整體價(jià)值。我們可以得到這樣的結(jié)論，底土耕作通過(guò)潛在的環(huán)境危害可能導(dǎo)致的嚴(yán)重降低，除非它是定期重復(fù)的。</p><p>　　關(guān)鍵詞：容

37、重，源渠道，底土，耕作</p><p><b>　　介紹</b></p><p>　　飽和土的滲透系數(shù)對(duì)農(nóng)業(yè)生產(chǎn)和環(huán)境保護(hù)都具有重要意義。飽和導(dǎo)水率，控制水滲透到土壤中，特別是在長(zhǎng)期內(nèi)。較低價(jià)值的與土壤表面的沖水，厭氧（降低）的土壤條件，徑流，洪水和侵蝕等有關(guān)。</p><p>　　特別重要的是耕種層下方土壤層的，這一層我們稱之為“底土”。在很

38、多情況下，這一層已被來(lái)自重型車輛以及對(duì)底部的耕作(如犁)的綜合壓力所壓實(shí)。在波蘭，主要耕作的深度通常是25 cm。“耕作層”(0-25厘米深)和“底土”(>25厘米深)往往具有相同的粒度分布，因此他們的水力特性可以直接進(jìn)行比較。</p><p><b>　　理論</b></p><p>　　土壤中的水電導(dǎo)率類似于一個(gè)電阻網(wǎng)絡(luò)的導(dǎo)電性。當(dāng)有明顯不同的運(yùn)輸方式時(shí)，土

39、壤可以作為一種簡(jiǎn)單的并行電阻網(wǎng)絡(luò)模型，如圖1所示。</p><p>　　圖1 通過(guò)微觀，中觀和宏觀結(jié)構(gòu)孔隙對(duì)土壤的電阻模擬。在這種情況下，電流是水流的模擬。</p><p>　　當(dāng)所有樣品具有相同的大小時(shí)，電導(dǎo)與電導(dǎo)率成正比。在這種情況下，電導(dǎo)率是加法因子，總電導(dǎo)率可以表示為：</p><p><b>　　(1)</b></p>

40、<p>　　本文中所述的波蘭土壤粘土含量低，并且宏觀結(jié)構(gòu)的特征，如干燥裂縫，通常不會(huì)發(fā)生。因此，我們可以假設(shè)，并只考慮前兩個(gè)條件。</p><p>　　由于K的取值范圍廣，我們繪制其取對(duì)數(shù)后的圖(以10為底)</p><p><b>　　(2)</b></p><p><b>　　土壤和實(shí)驗(yàn)方法</b></

41、p><p>　　土樣從波蘭四個(gè)不同的地點(diǎn)采集。關(guān)于采集地和土壤成分的信息見表1。從耕作層中采集的樣本通常從10-16厘米深度區(qū)間內(nèi)收集，從底土中采集的樣本通常是在30-36厘米深度區(qū)間內(nèi)收集。</p><p><b>　　表1 實(shí)驗(yàn)土壤</b></p><p>　　地點(diǎn)A和D位于我們研究所(永格)中的實(shí)驗(yàn)站點(diǎn)內(nèi)，而地點(diǎn)B和C是私</p>

42、;<p>　　立的，為一個(gè)商業(yè)農(nóng)場(chǎng)。沒(méi)有使用壓實(shí)處理。相反，已發(fā)現(xiàn)的不同密度的土壤作為一個(gè)在不同時(shí)期抽樣，使用不同作物輪作以及采用其他管理措施的結(jié)果出現(xiàn)。</p><p>　　飽和導(dǎo)水率的測(cè)量，使用了下降頭法(哈特格和浩 1992年)。的樣品直徑8厘米并有8厘米的長(zhǎng)度。凈容重的測(cè)量是在從100 cm3不銹鋼筒中收集的樣本中進(jìn)行的。</p><p><b>　　結(jié)果&

43、lt;/b></p><p>　　四個(gè)不同試驗(yàn)點(diǎn)的飽和滲透系數(shù)的測(cè)量值如圖2所示。這些圖上的每個(gè)點(diǎn)代表了的10個(gè)相似值的幾何平均數(shù)，并且，容重樣品的四個(gè)近似值的算術(shù)平均值是從一個(gè)很小的范圍(約1平方米)內(nèi)收集的。之所以使用幾何平均值，是因?yàn)檫@些值在實(shí)驗(yàn)誤差之內(nèi)已經(jīng)被證明是對(duì)數(shù)正態(tài)分布的，并且這個(gè)結(jié)論也已經(jīng)被貝克和鮑馬(1976)發(fā)現(xiàn)。log 和的典型平均值及其變化在表2中給出。這里必須注意，因?yàn)槿〉氖墙浦?/p>

44、，體積密度的S.E.值是S.D.值的一半;然而，對(duì)于log 0，其S.E.值大約是S.D.值的三分之一。</p><p>　　隨著容重的增加，已被經(jīng)常耕種的農(nóng)業(yè)表層的土壤在飽和導(dǎo)水率的對(duì)數(shù)中呈現(xiàn)線性下降趨勢(shì)。這可以表示為：</p><p><b>　　(3)</b></p><p>　　其中對(duì)于不同土壤a和b取不同的經(jīng)驗(yàn)值?；貧w線如圖2所示。a

45、和b的系數(shù)的值是通過(guò)對(duì)表3中實(shí)驗(yàn)土壤耕作層作回歸得到的。</p><p>　　圖2 在四個(gè)試驗(yàn)點(diǎn)中測(cè)量值的飽和導(dǎo)水率的值。表土中的測(cè)量值顯示為實(shí)心正方形，而底土的測(cè)量值用空心圓圈顯示。</p><p>　　表2 log和容重的典型平均值，它們的變化用其標(biāo)準(zhǔn)差表示</p><p>　　表3 對(duì)于實(shí)驗(yàn)土壤中的耕種層，方程(3)中a和b的系數(shù)</p>

46、<p>　　括號(hào)中的值是標(biāo)準(zhǔn)誤差，不確定：也不適用。</p><p>　　土壤下層有一個(gè)相似的粒子規(guī)模分布，這些地方的水力傳導(dǎo)值通常比方程(3)中相關(guān)表土的值大。圖2說(shuō)明了這一點(diǎn)，其中底土的值(如空心圓圈所示)大多高于相應(yīng)耕作層表土的回歸線。對(duì)于已調(diào)查過(guò)的波蘭沙質(zhì)土壤，我們將“過(guò)剩的”水力傳導(dǎo)歸咎于中間毛孔，這通常是以源渠道的形式存在的。</p><p>　　我們已經(jīng)通過(guò)用實(shí)測(cè)值

47、減去由方程(3)結(jié)合表3提供的系數(shù)得出的預(yù)測(cè)值來(lái)調(diào)查這個(gè)“過(guò)剩的”水力傳導(dǎo)。這可以得到。在這些計(jì)算中，通過(guò)方程(1)和方程(2)，我們使用的值而不是。的“過(guò)剩的”的值與土壤B, C及D的值結(jié)合后再進(jìn)行計(jì)算，因?yàn)榭捎玫闹禂?shù)量有限。合并后的值的對(duì)數(shù)分布可擬合為正態(tài)分布。由此產(chǎn)生的概率圖如圖3所示。這個(gè)正態(tài)分布有的一個(gè)均值及的一個(gè)標(biāo)準(zhǔn)差。夏皮羅-威爾克的一個(gè)常態(tài)測(cè)試表明，這些數(shù)據(jù)可給出并且這些數(shù)據(jù)分布在0.05的范圍內(nèi)(夏皮羅和威爾克，196

48、5年)。</p><p>　　圖3 表土中(ms-1)“過(guò)?！敝祵?duì)數(shù)的正常概率圖</p><p>　　我們可以通過(guò)增加微結(jié)構(gòu)電導(dǎo)率，以及根據(jù)方程(1)和方程(2)得到的假設(shè)的微結(jié)構(gòu)電導(dǎo)率，典型土壤來(lái)看看這個(gè)公式的含義。對(duì)于微觀結(jié)構(gòu)的導(dǎo)電性，我們可以使用方程(3)并結(jié)合表3給出的平均系數(shù)。對(duì)于微觀結(jié)構(gòu)的電導(dǎo)率，我們可以使用圖3所示的正態(tài)分布所給出的平均值。這可以產(chǎn)生如圖4所示的圖形。<

49、;/p><p>　　圖4 底土中微觀和中觀結(jié)構(gòu)的假設(shè)例子對(duì)不同容重的飽和導(dǎo)水率的影響。陰影區(qū)域顯示，如果中孔（如根通道）被摧毀，滲透系數(shù)可能丟失。</p><p>　　如圖4中的例子所示，在容重值約1.575 mg/m-3時(shí)，微觀和中觀結(jié)構(gòu)毛孔對(duì)飽和導(dǎo)水率的貢獻(xiàn)是相同的。當(dāng)容重小于這個(gè)值時(shí)，微觀結(jié)構(gòu)的貢獻(xiàn)為主，而在容重大于這個(gè)值時(shí)，中觀結(jié)構(gòu)占主導(dǎo)地位。盡管圖4是現(xiàn)實(shí)的，我們卻必須切記如圖3和圖

50、4所示，的值可能由于至少100中因素的影響而變化。這一事實(shí)說(shuō)明單獨(dú)通過(guò)結(jié)構(gòu)性土壤的容重來(lái)準(zhǔn)確預(yù)測(cè)是不可能的。</p><p><b>　　5 結(jié)論</b></p><p>　　我們的結(jié)論是：波蘭土和沙質(zhì)底土的“過(guò)剩”飽和導(dǎo)水率是由于細(xì)觀毛孔的存在，通常以根渠道的形式存在。這些細(xì)觀毛孔，可以極大地增加底土的滲透系數(shù)。盡管在我們所調(diào)查的沙質(zhì)土壤中蚯蚓并不常見，然而在有些

51、土壤中，蚯蚓隧道也可以大幅度的增加的值。</p><p>　　細(xì)觀毛孔特征的作用，如根渠道的作用，在表土和底土中土壤顆粒密度分布相同的情況下很容易描述，在土壤顆粒密度分布不同的情況下，這個(gè)作用的也被認(rèn)為是相似的。</p><p>　　有關(guān)這些發(fā)現(xiàn)的一個(gè)合乎邏輯的結(jié)果是，：底土中耕作的深度，假如40 cm，會(huì)破壞現(xiàn)有地基的細(xì)觀結(jié)構(gòu)。我們已經(jīng)發(fā)現(xiàn)，深松后，在顆粒密度相似或密度更大的土壤中可以隨

52、時(shí)重排。但是，這可以在沒(méi)有細(xì)觀結(jié)構(gòu)的情況下進(jìn)行重排，并且將會(huì)比深耕(或深松)前有更低的值。</p><p>　　因此，我們可以得出結(jié)論，在地基結(jié)構(gòu)可能遭破壞或可能重排的地方，不宜進(jìn)行深耕。在這種情況下，通過(guò)減小的值，底土耕作可能嚴(yán)重影響水沖擊力，徑流和侵蝕的增加。在底土高度壓縮的地方，對(duì)細(xì)觀結(jié)構(gòu)損失的影響將更加嚴(yán)重。</p><p><b>　　參考文獻(xiàn)：</b>&l

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