【经典外文翻译】--底土的土壤结构和饱和导水率—-毕业论文设计.doc

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1、英文原文：Low-cost programmable pulse generator for particle telescope calibrationAbstractIn this paper we 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 det

2、ector channel on the telescope. 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 telescopes prior to calibration at accelerator. This task inclu

3、des evaluation of linearity and resolution of each detector channel, as well as coincidence logic. The heights of the pulses sent to the detectors are obtained by Monte Carlo simulation of telescope response to a particle flux of any desired geometry and composition. Elsevier Science B.V. All rights

4、 reserved.To assure a correct interpretation of data obtained with scientific instruments onboard satellites, as well as to compare these data with those of similar instruments, a thorough pre-flight calibration is required. For solar and cosmic ray particle telescopes, this calibration is usually c

5、arried out in two steps: first, a calibration of each individual detector using radioactive sources and standard nuclear instrumentation (NIM or CAMAC modules),following by a final test of the whole telescope performed in a particle accelerator site. The success of calibration on accelerator require

6、s that, prior to the experiences, all detectors and electronics parameter (polarization voltages, amplifier gains and shaping times, thresholds, etc.) have nearly definitive values. Here we propose a cheap and simple pre-calibration procedure based on a new system that we have called Programmable Pu

7、lse Generator (PPG). The PPG developed in our laboratory has been designed for a specific instrument, a four-detector cosmic ray telescope, but it can easily be modified for similar experiments.The standard calibration procedure for individual detectors and their electronic chains consists of introd

8、ucing 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 pulse generators do present several limitations: The pulse amplitude must be set manually. Thus, to generate the pu

9、lses that different particles with different energies would release on the detectors, it is necessary to change the pulse heights every time.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 t

10、he single output in order to get several signals. It is difficult to check the coincidence logic because the four signals are not independent.To overcome these difficulties, pulse generators of programmable amplitude and rate have been proposed. Abdel-Aal 1presented a programmable random pulse gener

11、ator 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 converter(DAC),thus having the temporal characteristics of the DAC output. Our purpose is to generate variable height analog pulses with si

12、milar shape to that released by nuclear detectors.The low-cost PPG presented 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 proposed pre-cal

13、ibration 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 individual event, the energy signal data are sent through a bidirectional RS-232-C line

14、to the PPG, which transforms the results of the simulation into real pulses and sends them to the real instrument.Fig 1 2 PPG descriptionThe design of the PPG is divided into two functional modules: digital electronics and analog electronics, whose block diagrams are enclosed in dashed boxes shown i

15、n Fig2. The data arriving at the digital module from the PC are sent to 12 bit DAC. The DAC output voltages are transformed in the analog module into suitable pulses, ready to be introduced into the test input of the related detector channel of the telescope.Analog and digital modules are described

16、with some detail in Sections 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.2.1 Analog moduleThis module must be capable of producing signal pulses similar to those generated in the detectors by the passage of energeti

17、c charged particles, whose shape can be described by the following function: (1)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, typical values for and are approx

18、imately 5 ns and 10 us, respectively.Our particular telescope has four detectors, therefore four almost simultaneous pulses with different amplitudes have to be generated for each simulated event. These amplitudes are sent by the digital module to the analog module, together with a start pulse (see

19、Fig 2). The communication is performed through a coupler circuit for isolation purposes. 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 each multiplier is this reference pulse, and the other is one of

20、the DAC amplitude signals. Thus, every multiplier acts as a modulator: when the reference pulse arrives, the multiplier generates a similar pulse whose amplitude is the respective voltage given by the digital module.The reference pulse generator is the most critical element in the system, because an

21、y 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 arrives to the reference pulse generator, the capacitoris charged at voltage, ultra-precision, guaranteed long-term drift

22、 voltage reference has been used for this purpose (MAX677BCPP). Once the capacitor present stable voltage and a start pulse is generated, this capacitor is connected to switching the relay . In order to avoid the characteristic glitches of the mechanic relays, a mercury relay has been used. Mikhailo

23、v2has pointed out recently the limited pulse rate (100 pps) achievable with mercury relays, but we focuses on modulating the pulse amplitude rather than reaching a high pulse rate. When is connected to, the equations describing the evolution of the circuit of Fig3 are the following: (2)The solution

24、of this linear system with the conditions and gives an output pulse with the functional form (1) and amplitude. Though the rise and fall times depend on resistor and capacitor values through a complicated algebraic expression, for (condition fulfilled here) the following approximate expressions hold

25、: (3)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 Fig 4 .Fig 4. Oscilloscope images of the reference pulse rise (left) and fall (right) flanges. The quot

26、ed values of rise and fall time refer to 10-90%of the amplitude. The values of and in the text refer to 1/e of the amplitude.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 these restrict

27、ions, 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.In order to respond to the high-frequency components of the reference pulse (rise time5 ns), the multiplier AD834, which presents 4

28、 ns transition time, has been chosen. The output range provided by the multipliers 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 suitab

29、le 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.中文翻译：底土的土壤结构和饱和导水率摘要饱和导水率，是在从耕作层和底土中采集来的土壤样品上衡量的。自然产生的土壤容重的范围，是通过对不同年份有或没有轮轨的不同作物取样而得来的。据研究发现，对耕作层来

30、说，的对数与容重之间存在着相当好的线性关系。然而，对于底土，的价值通常在于能发现相应耕作层的回归线。底土的这种过度的导水率，是由于水力传导的生物过程，尤其是源渠道的存在。耕作层较低的渗透系数，相对于底土，是由于这些生物过程被耕作破坏。已经提出了一种简单的模型，在这种模型中，土壤质地和渠道根源都分别有利于的整体价值。我们可以得到这样的结论，底土耕作通过潜在的环境危害可能导致的严重降低，除非它是定期重复的。关键词：容重，源渠道，底土，耕作1 介绍 饱和土的渗透系数对农业生产和环境保护都具有重要意义。饱和导水率，控制水渗透到土壤中，特别是在长期内。较低价值的与土壤表面的冲水，厌氧（降低）的土壤条件，

31、径流，洪水和侵蚀等有关。特别重要的是耕种层下方土壤层的，这一层我们称之为“底土”。在很多情况下，这一层已被来自重型车辆以及对底部的耕作(如犁)的综合压力所压实。在波兰，主要耕作的深度通常是25 cm。“耕作层”(0-25厘米深)和“底土”(25厘米深)往往具有相同的粒度分布，因此他们的水力特性可以直接进行比较。2 理论土壤中的水电导率类似于一个电阻网络的导电性。当有明显不同的运输方式时，土壤可以作为一种简单的并行电阻网络模型，如图1所示。图1 通过微观，中观和宏观结构孔隙对土壤的电阻模拟。在这种情况下，电流是水流的模拟。当所有样品具有相同的大小时，电导与电导率成正比。在这种情况下，电导率是加法

32、因子，总电导率可以表示为： (1)本文中所述的波兰土壤粘土含量低，并且宏观结构的特征，如干燥裂缝，通常不会发生。因此，我们可以假设，并只考虑前两个条件。由于K的取值范围广，我们绘制其取对数后的图(以10为底) (2)3 土壤和实验方法土样从波兰四个不同的地点采集。关于采集地和土壤成分的信息见表1。从耕作层中采集的样本通常从10-16厘米深度区间内收集，从底土中采集的样本通常是在30-36厘米深度区间内收集。表1 实验土壤地点A和D位于我们研究所(永格)中的实验站点内，而地点B和C是私立的，为一个商业农场。没有使用压实处理。相反，已发现的不同密度的土壤作为一个在不同时期抽样，使用不同作物轮作以及

33、采用其他管理措施的结果出现。饱和导水率的测量，使用了下降头法(哈特格和浩 1992年)。的样品直径8厘米并有8厘米的长度。净容重的测量是在从100 cm3不锈钢筒中收集的样本中进行的。4 结果四个不同试验点的饱和渗透系数的测量值如图2所示。这些图上的每个点代表了的10个相似值的几何平均数，并且，容重样品的四个近似值的算术平均值是从一个很小的范围(约1平方米)内收集的。之所以使用几何平均值，是因为这些值在实验误差之内已经被证明是对数正态分布的，并且这个结论也已经被贝克和鲍马(1976)发现。log 和的典型平均值及其变化在表2中给出。这里必须注意，因为取的是近似值，体积密度的S.E.值是S.D.

34、值的一半;然而，对于log 0，其S.E.值大约是S.D.值的三分之一。随着容重的增加，已被经常耕种的农业表层的土壤在饱和导水率的对数中呈现线性下降趋势。这可以表示为： (3)其中对于不同土壤a和b取不同的经验值。回归线如图2所示。a和b的系数的值是通过对表3中实验土壤耕作层作回归得到的。图2 在四个试验点中测量值的饱和导水率的值。表土中的测量值显示为实心正方形，而底土的测量值用空心圆圈显示。表2 log和容重的典型平均值，它们的变化用其标准差表示表3 对于实验土壤中的耕种层，方程(3)中a和b的系数括号中的值是标准误差，不确定：也不适用。土壤下层有一个相似的粒子规模分布，这些地方的水力传导值

35、通常比方程(3)中相关表土的值大。图2说明了这一点，其中底土的值(如空心圆圈所示)大多高于相应耕作层表土的回归线。对于已调查过的波兰沙质土壤，我们将“过剩的”水力传导归咎于中间毛孔，这通常是以源渠道的形式存在的。我们已经通过用实测值减去由方程(3)结合表3提供的系数得出的预测值来调查这个“过剩的”水力传导。这可以得到。在这些计算中，通过方程(1)和方程(2)，我们使用的值而不是。的“过剩的”的值与土壤B, C及D的值结合后再进行计算，因为可用的值数量有限。合并后的值的对数分布可拟合为正态分布。由此产生的概率图如图3所示。这个正态分布有的一个均值及的一个标准差。夏皮罗-威尔克的一个常态测试表明，

36、这些数据可给出并且这些数据分布在0.05的范围内(夏皮罗和威尔克，1965年)。图3 表土中(ms-1)“过剩”值对数的正常概率图我们可以通过增加微结构电导率，以及根据方程(1)和方程(2)得到的假设的微结构电导率，典型土壤来看看这个公式的含义。对于微观结构的导电性，我们可以使用方程(3)并结合表3给出的平均系数。对于微观结构的电导率，我们可以使用图3所示的正态分布所给出的平均值。这可以产生如图4所示的图形。图4 底土中微观和中观结构的假设例子对不同容重的饱和导水率的影响。阴影区域显示，如果中孔（如根通道）被摧毁，渗透系数可能丢失。如图4中的例子所示，在容重值约1.575 mg/m-3时，微观

37、和中观结构毛孔对饱和导水率的贡献是相同的。当容重小于这个值时，微观结构的贡献为主，而在容重大于这个值时，中观结构占主导地位。尽管图4是现实的，我们却必须切记如图3和图4所示，的值可能由于至少100中因素的影响而变化。这一事实说明单独通过结构性土壤的容重来准确预测是不可能的。5 结论我们的结论是：波兰土和沙质底土的“过剩”饱和导水率是由于细观毛孔的存在，通常以根渠道的形式存在。这些细观毛孔，可以极大地增加底土的渗透系数。尽管在我们所调查的沙质土壤中蚯蚓并不常见，然而在有些土壤中，蚯蚓隧道也可以大幅度的增加的值。细观毛孔特征的作用，如根渠道的作用，在表土和底土中土壤颗粒密度分布相同的情况下很容易描

38、述，在土壤颗粒密度分布不同的情况下，这个作用的也被认为是相似的。有关这些发现的一个合乎逻辑的结果是，：底土中耕作的深度，假如40 cm，会破坏现有地基的细观结构。我们已经发现，深松后，在颗粒密度相似或密度更大的土壤中可以随时重排。但是，这可以在没有细观结构的情况下进行重排，并且将会比深耕(或深松)前有更低的值。因此，我们可以得出结论，在地基结构可能遭破坏或可能重排的地方，不宜进行深耕。在这种情况下，通过减小的值，底土耕作可能严重影响水冲击力，径流和侵蚀的增加。在底土高度压缩的地方，对细观结构损失的影响将更加严重。参考文献：Baker, F.G., Bouma, J., 1976. Variab

39、ility of hydraulic conductivityin two subsurface horizons of two silt loam soils. Soil Sci. Soc.Am. J. 40, 219222.Hartge, K.H., Horn, R., 1992. Die Physikalische Untersuchen vonBo den., Enke Verlag, Stuttgart.Horn, R., Kretschmer, H., Baumgartl, T., Bohne, K., Neupert, A.,Dexter, A.R., 1998. Soil mechanical properties of a partly-reloosened (slit plough system) and a conventionally-tilledoverconsolidated gleyic Luvisol derived from glacial till. Int.Agrophys. 12 (3), 143154.Shapiro, S.S., Wilk, M.B., 1965. An analysis of variance test fornormality. Biometrika 52, 591611.