外文翻譯--底土的土壤結構和飽和導水率

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>　　底土的土壤結構和飽和導水率</p><p><b>　　摘要</b></p><p>　　飽和導水率，是在從耕作層和底土中采集來的土壤樣品上衡量的。自然產生的土壤容重的范圍，是通過對不同年份有或沒有輪軌的不同作物取樣而得來的。據研究發(fā)現，對耕作層來說，的對數與容重之間存

36、在著相當好的線性關系。然而，對于底土，的價值通常在于能發(fā)現相應耕作層的回歸線。底土的這種過度的導水率，是由于水力傳導的生物過程，尤其是源渠道的存在。耕作層較低的滲透系數，相對于底土，是由于這些生物過程被耕作破壞。已經提出了一種簡單的模型，在這種模型中，土壤質地和渠道根源都分別有利于的整體價值。我們可以得到這樣的結論，底土耕作通過潛在的環(huán)境危害可能導致的嚴重降低，除非它是定期重復的。</p><p>　　關鍵詞：容

37、重，源渠道，底土，耕作</p><p><b>　　介紹</b></p><p>　　飽和土的滲透系數對農業(yè)生產和環(huán)境保護都具有重要意義。飽和導水率，控制水滲透到土壤中，特別是在長期內。較低價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。</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，這一層已被來自重型車輛以及對底部的耕作(如犁)的綜合壓力所壓實。在波蘭，主要耕作的深度通常是25 cm?！案鲗印?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行比較。</p><p><b>　　理論</b></p><p>　　土壤中的水電導率類似于一個電阻網絡的導電性。當有明顯不同的運輸方式時，土

39、壤可以作為一種簡單的并行電阻網絡模型，如圖1所示。</p><p>　　圖1 通過微觀，中觀和宏觀結構孔隙對土壤的電阻模擬。在這種情況下，電流是水流的模擬。</p><p>　　當所有樣品具有相同的大小時，電導與電導率成正比。在這種情況下，電導率是加法因子，總電導率可以表示為：</p><p><b>　　(1)</b></p>

40、<p>　　本文中所述的波蘭土壤粘土含量低，并且宏觀結構的特征，如干燥裂縫，通常不會發(fā)生。因此，我們可以假設，并只考慮前兩個條件。</p><p>　　由于K的取值范圍廣，我們繪制其取對數后的圖(以10為底)</p><p><b>　　(2)</b></p><p><b>　　土壤和實驗方法</b></

41、p><p>　　土樣從波蘭四個不同的地點采集。關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)間內收集。</p><p><b>　　表1 實驗土壤</b></p><p>　　地點A和D位于我們研究所(永格)中的實驗站點內，而地點B和C是私</p>

42、;<p>　　立的，為一個商業(yè)農場。沒有使用壓實處理。相反，已發(fā)現的不同密度的土壤作為一個在不同時期抽樣，使用不同作物輪作以及采用其他管理措施的結果出現。</p><p>　　飽和導水率的測量，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厘米的長度。凈容重的測量是在從100 cm3不銹鋼筒中收集的樣本中進行的。</p><p><b>　　結果&

43、lt;/b></p><p>　　四個不同試驗點的飽和滲透系數的測量值如圖2所示。這些圖上的每個點代表了的10個相似值的幾何平均數，并且，容重樣品的四個近似值的算術平均值是從一個很小的范圍(約1平方米)內收集的。之所以使用幾何平均值，是因為這些值在實驗誤差之內已經被證明是對數正態(tài)分布的，并且這個結論也已經被貝克和鮑馬(1976)發(fā)現。log 和的典型平均值及其變化在表2中給出。這里必須注意，因為取的是近似值

44、，體積密度的S.E.值是S.D.值的一半;然而，對于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，已被經常耕種的農業(yè)表層的土壤在飽和導水率的對數中呈現線性下降趨勢。這可以表示為：</p><p><b>　　(3)</b></p><p>　　其中對于不同土壤a和b取不同的經驗值?；貧w線如圖2所示。a

45、和b的系數的值是通過對表3中實驗土壤耕作層作回歸得到的。</p><p>　　圖2 在四個試驗點中測量值的飽和導水率的值。表土中的測量值顯示為實心正方形，而底土的測量值用空心圓圈顯示。</p><p>　　表2 log和容重的典型平均值，它們的變化用其標準差表示</p><p>　　表3 對于實驗土壤中的耕種層，方程(3)中a和b的系數</p>

46、<p>　　括號中的值是標準誤差，不確定：也不適用。</p><p>　　土壤下層有一個相似的粒子規(guī)模分布，這些地方的水力傳導值通常比方程(3)中相關表土的值大。圖2說明了這一點，其中底土的值(如空心圓圈所示)大多高于相應耕作層表土的回歸線。對于已調查過的波蘭沙質土壤，我們將“過剩的”水力傳導歸咎于中間毛孔，這通常是以源渠道的形式存在的。</p><p>　　我們已經通過用實測值

47、減去由方程(3)結合表3提供的系數得出的預測值來調查這個“過剩的”水力傳導。這可以得到。在這些計算中，通過方程(1)和方程(2)，我們使用的值而不是。的“過剩的”的值與土壤B, C及D的值結合后再進行計算，因為可用的值數量有限。合并后的值的對數分布可擬合為正態(tài)分布。由此產生的概率圖如圖3所示。這個正態(tài)分布有的一個均值及的一個標準差。夏皮羅-威爾克的一個常態(tài)測試表明，這些數據可給出并且這些數據分布在0.05的范圍內(夏皮羅和威爾克，196

48、5年)。</p><p>　　圖3 表土中(ms-1)“過?！敝祵档恼８怕蕡D</p><p>　　我們可以通過增加微結構電導率，以及根據方程(1)和方程(2)得到的假設的微結構電導率，典型土壤來看看這個公式的含義。對于微觀結構的導電性，我們可以使用方程(3)并結合表3給出的平均系數。對于微觀結構的電導率，我們可以使用圖3所示的正態(tài)分布所給出的平均值。這可以產生如圖4所示的圖形。<

49、;/p><p>　　圖4 底土中微觀和中觀結構的假設例子對不同容重的飽和導水率的影響。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，微觀和中觀結構毛孔對飽和導水率的貢獻是相同的。當容重小于這個值時，微觀結構的貢獻為主，而在容重大于這個值時，中觀結構占主導地位。盡管圖4是現實的，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。這一事實說明單獨通過結構性土壤的容重來準確預測是不可能的。</p><p><b>　　5 結論</b></p><p>　　我們的結論是：波蘭土和沙質底土的“過剩”飽和導水率是由于細觀毛孔的存在，通常以根渠道的形式存在。這些細觀毛孔，可以極大地增加底土的滲透系數。盡管在我們所調查的沙質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，這個作用的也被認為是相似的。</p><p>　　有關這些發(fā)現的一個合乎邏輯的結果是，：底土中耕作的深度，假如40 cm，會破壞現有地基的細觀結構。我們已經發(fā)現，深松后，在顆粒密度相似或密度更大的土壤中可以隨

52、時重排。但是，這可以在沒有細觀結構的情況下進行重排，并且將會比深耕(或深松)前有更低的值。</p><p>　　因此，我們可以得出結論，在地基結構可能遭破壞或可能重排的地方，不宜進行深耕。在這種情況下，通過減小的值，底土耕作可能嚴重影響水沖擊力，徑流和侵蝕的增加。在底土高度壓縮的地方，對細觀結構損失的影響將更加嚴重。</p><p><b>　　參考文獻：</b>&l

53、t;/p><p>　　Baker, F.G., Bouma, J., 1976. Variability of hydraulic conductivity</p><p>　　in two subsurface horizons of two silt loam soils. Soil Sci. Soc.</p><p>　　Am. J. 40, 219–222.&l

54、t;/p><p>　　Hartge, K.H., Horn, R., 1992. Die Physikalische Untersuchen von</p><p>　　Bo ¨den., Enke Verlag, Stuttgart.</p><p>　　Horn, R., Kretschmer, H., Baumgartl, T., Bohne, K.,

55、Neupert, A.,</p><p>　　Dexter, A.R., 1998. Soil mechanical properties of a partly-</p><p>　　reloosened (slit plough system) and a conventionally-tilled</p><p>　　overconsolidated gley

56、ic Luvisol derived from glacial till. Int.</p><p>　　Agrophys. 12 (3), 143–154.</p><p>　　Shapiro, S.S., Wilk, M.B., 1965. An analysis of variance test for</p><p>　　normality. Biometr