THE TIMES REQUIRED FOR THE ATTAINMENT OF AIR-WATER EQUILIBRIUM IN CLAY SOILS

The coefficient of diffusion of air through the pore water of clay soils has been measured directly and has been shown to be markedly less than for free water and to decrease with water content. It has been shown that these low coefficients of diffusion are not accounted for by the sinuosity of the flow channels, or by any important departure from Henry's law of solution at curved air-water interfaces. The main factors appear to be constrictions in the flow channels and the reduced viscosity of the adsorbed water. It is concluded that air-water equilibrium in partly saturated soils will be attained much more slowly than is generally assumed.     

Zein Batch Extraction from Dry-Milled Corn: Cereal Disintegration by Dissolving Fluid Shear

Corn particles were extracted in an agitated vessel with a 4:1 mass ratio of 70% ethanol to corn for periods of 1–6 hr at ambient temperature. The extract solution was filtered and centrifuged to remove suspended particles after extraction and then diluted to 40% ethanol to precipitate extracted solute. Measurements of the mass of suspended particles separated by centrifugation indicate that mixing the corn particles with the ethanol dissolves and weakens the protein between cells and between starch granules within cells near the particles' surface. Under the conditions of this study, corn particles release starch granules more rapidly than the protein bodies dissolve, as indicated by analysis of the centrifuged particles. The diffusion coefficient for ethanol solution in corn was estimated and compared with a coefficent derived from a fit of the trend in the rate of release of fine particles from the milled corn. The diffusion coefficient of pure zein in a stagnant 70% ethanol solution was estimated from the measurement of weight loss by a ball of zein. Analysis of the ambient temperature protein extraction rate indicates that 2-mm particles exhibit more convective mass transfer than 20-μm particles.     

THE MEASUREMENT AND MECHANISM OF ION DIFFUSION IN SOILS

Integral diffusion coefficients for K in two contrasting soils, containing different levels of exchangeable K, are calculated from measurements of diffusive flux to a hydrogen resin paper. The diffusion coefficients are larger, the higher the exchangeable K level or moisture content. Diffusive flux of K in these soils can be accounted for entirely by diffusion through the soil solution in the pores. Impedance factors calculated compare satisfactorily with values for similar soils reported by other workers. The concentration dependence of the diffusion coefficient is shown to be causally related to the nature of the sorption isotherm. A method for estimating the differential diffusion coefficient at any concentration is described. It can also be calculated from the slope of the sorption isotherm at the chosen concentration, if the value of the impedance factor at the relevant moisture content is known and if diffusion other than through solution only is negligible.     

Bacterial air pollution from an activated sludge tank

Concentrations of air-borne coliforms and ‘other’ bacteria (defined as total bacteria minus coliforms) were measured. downwind of a sewage treatment plant activated sludge tank. The Gaussian plume diffusion equation adequately predicts concentrations of the ‘other’ bacteria; the diffusion equation must be modified by an extinction coefficient, equivalent to a half-life of about 7.4 s, to predict coliform concentrations. Coliform concentrations downwind of this tank did not present a significant health hazard, but the method is applicable to treatment plants of higher capacity and possibly greater emissions.     

Diffusion of cattle manure solution through a wet porous stratum with reaction

A process governing the transport rate of cattle manure as measured by their COD (chemical oxygen demand) through a wet porous stratum is investigated under simulated conditions. A mathematical model of the system is presented. The model simulates diffusion and biological reaction processes taking place simultaneously in the system. Experimental observations have been made to determine the diffusion coefficient and the biological reaction rate constant of the cattle manure solution. Values of approximately 6.76 × 10^?6 cm² s^?1 for the diffusion coefficient and 3.05 × 10^?2 day^?1 for the reaction rate constant at the temperature of 25 ± 2°C were obtained. For the system with known diffusion coefficient and reaction rate constant, the analytical expressions obtained here can be used to approximately evaluate or predict the rates that animal wastes, under conditions similar to those in this study, will contaminate surface water, soil or ground water.     

磁场及流速场条件下盐渍液快速腌渍芥菜

为了实现对芥菜的快速腌渍,采用磁场和流动盐液相结合的方式对样品进行处理,并与静置条件下的腌渍进行了对比。利用不同磁感应强度的磁场(200、1 000、2 000 Gs)和流速场(0.03、0.06、0.22 m/s)完成对芥菜的腌渍处理,同时考察了传质动力学方程。结果表明:当腌渍条件于磁感应强度2 000 Gs和流速0.06 m/s时,可在180 min时间内使样品表层盐分达到饱和,盐分扩散系数为k=2.35×10-2 min-1,而当腌渍液处于湍流(0.22 m/s,雷诺数Re=4 132)的情况下则不利于盐分扩散,只施加磁场的静置腌渍对传质无显著提高(P0.05),而当腌渍液在层流状态下(雷诺数Re=563和1 127)则有利于盐分向多孔状原料的渗透,最佳工艺参数为磁感应强度B=2 000 Gs和流速v=0.06 m/s且该条件下的传质动力学模型可采用Logistic方程进行描述,预测方程决定系数为R2=0.976,该研究为农产品快速浸渍加工提供了参考。     

基于光电传感技术的薄层水流流速测量系统构建与试验

为减小染色法测量坡面水流流速的误差,提高染色法测量准确度,根据染色示踪剂在水中扩散引起颜色发生变化的特性,结合漫反射型模拟量光电颜色传感器和数据采集卡采集信号,通过小波变换对信号进行去噪,研发一种基于光电传感技术的薄层水流流速测量系统。以流量法为参照,确定该系统传感器最优数据采集距离为0.6～0.8 m;传感器数据采集距离为0.7 m时,该系统测量数据最小相对误差仅为0.48%,变异系数15%。相比染色法,该系统与流量法拟合的决定系数在0.90以上,大于染色法的决定系数0.75。表明薄层水流流速测量系统优于染色法,可以用坡面薄层水流试验研究中。     

An improved universal extracting solution and its use for diagnosing soil fertility

Abstract

An improved universal soil extracting solution prepared by adding DTPA to Morgan's solution is presented. As with the Morgan's solution, it is possible to determine all important elements except sodium in a single extract but with better correlations of extracted trace elements with plant growth.

Methods for determination of important elements are given along with suggested treatments to change undesirable levels of elements to favorable ones.

Maximum value is obtained from use of the extracting solution by determination of soluble N along with other elements in soil samples collected frequently from same crop.     

果蔬类多孔介质干燥传质过程的分子动力学模拟

果蔬类多孔介质内部水中溶解有大量的营养物质(溶质),在干燥过程中溶质的迁移与湿分的传递同时进行,其内部微孔内的干燥传质机理尚不明确。为了揭示果蔬类多孔介质干燥过程中内部溶液的迁移机理,确定果蔬微孔结构特性对干燥传质过程的影响规律,该研究采用分子动力学方法模拟研究了果蔬类多孔介质微孔道中的干燥传质过程,构建了光滑壁面溶液扩散过程模型与粗糙壁面溶液扩散过程模型。模拟过程采用SPC/E水分子模型,选取OPLS-AA全原子力场和正则系综,溶液势函数选用静电库伦相互作用与Lennard-Jones相互作用,中心水分子的初始速度由高斯分布给出,采用Velocity-Verlet算法,用SHAKE算法固定水分子,x、y方向施加周期性边界条件,z方向上施加固定壁面边界条件。从分子水平模拟分析了果蔬类多孔介质内部溶液的扩散过程,并以马铃薯的热风干燥试验结果进行模型的验证。得出试验值与KCl溶液粗糙壁面模型的模拟值最为接近,其最大相对误差为17.39%;与纯水模型的模拟值相差最大,说明溶质的存在对水分扩散系数的影响不可忽略,且粗糙壁面模型更接近于真实孔道结构。从径向分布函数分布可以看出K+、Cl-对水分子...     

THE MEASUREMENT AND MECHANISM OF ION DIFFUSION IN SOILS

The counter-diffusion of phosphate against chloride was measured in a moisture-saturated block of soil by following the efflux of phosphate into a limited volume of well-stirred CaCl₂ solution, of the same ionic composition as the soil-pore solution except for a lower initial phosphate concentration. By varying this phosphate concentration effective diffusion coefficients over a wide range of depletion were measured. The fraction of labile phosphate desorbed, and the relation between phosphate desorbed and concentration of phosphate in the equilibrium solution were measured in the same experiments. Effective diffusion coefficients varied from 0.43 to 1.50 × 10^-4cm² sec^-1, tending to decrease as depletion increased. Depletions ranged from about 0.3 to 25 per cent of the ³²P exchangeable phosphate, which corresponded to a lowering of the solution concentration by about 30 to 65 per cent of the initial concentrations. Diffusive movement of phosphate in this soil can be accounted for by diffusion through the liquid pathway only. The effective diffusion coefficient can be predicted from phosphate desorbed in response to a change in the concentration of the equilibrium solution, and an impedance factor.     

基于改进关联方法的河北省农产品加工主导产业选择

为准确把握河北省农产品加工业发展的优劣势,确定应重点扶持的主导产业,该文借鉴中国学者邓聚龙提出的灰色系统理论,对邓氏关联度模型的适用条件进行剖析,提出在研究数据顺序可以调整的行为指标序列关联度问题时,用区间值象代替初值象或均值象,用1和0代替绝对差值最大最小取值的改进思路,以解决因序列始点数据和参照序列变化带来计算结果不唯一以及无量纲化处理可能破坏数据内在关系等问题;从投入产出理论产业关联的本质内涵分析,提出在研究某部门对国民经济的影响力大小时,通过构建虚拟最优前向后向效应参照序列,综合分析其与所有部门的关联效应的优化思路,以更客观真实地反映该部门的拉动推动作用。以2012年河北省139部门投入产出表和2013-2016年农产品加工业统计资料为基础数据来源,采用改进关联度分析方法对17类农产品加工业部门进行综合评价,结果表明:河北省皮毛羽丝加工、棉麻纺织业主营业务收入比例分别位居全省第1、第2位,加权综合优势评价分别位居全省第1、第2位,关联度综合优势评价分别位居全省第2、第1位;中药加工、乳品加工、粮食加工、植物油加工、果蔬加工业加权综合优势评价分别位居全省第4、第5、第6、第7、第8位,关联度综合优势评价分别位居全省第7、第4、第9、第8、第11位,应作为主导产业有针对性地予以重点扶持。研究结果对河北省实施农产品加工业提升行动有参考价值。     

改进型深筒式消力井消能效果及影响因素分析

为优化深筒式消力井装置的结构,使其在增加消能率的同时而不影响水流平顺流入下一级管道,并能降低水流对消力井井底的冲刷破坏作用,通过理论分析和模型试验研究,测量了消力井的相关水力参数,计算了不同结构体型消力井的水头损失系数和消能率,从消能率的角度探讨了多喷孔出水口的结构参数、溢流板高度与水头损失系数之间的关系,结合井底压强分布情况寻找较优的结构体型。结果表明:采用多喷孔出水口并增设溢流板的改进Ⅱ型消力井消能率比传统型的要高30%且井底压强分布均匀,在结构上具有明显优势。改进Ⅱ型消力井在小流量情况下过堰水流为自由出流,此时消力井水头损失系数会随流量的增加而降低,当流量增加至淹没出流后消力井水头损失系数随流量变化不明显。相对开孔面积为100%时,消力井主井水头损失系数随喷孔孔径的增加会有小幅度的减小;在距径比不大于2.5时水头损失系数随距径比的增大而减小,距径比大于2.5之后对水头损失系数影响不大;喷孔错列布置的水头损失系数明显比并列布置的大;溢流板高度对消力井水头损失系数的影响不明显,在淹没出流时堰板高度小的消力井水头损失系数略微有所降低。此研究可为深筒式消力井的结构设计提供参考,亦可为解决长距离管道输水过程中的消能问题提供科学依据。     

Boundary conditions for the waste stabilization pond

Two different solutions of the dispersed flow model of the waste stabilization pond based on two different sets of boundary conditions were compared and analyzed statistically. These solutions, used in the prediction of the coliform reduction in the pond, were based on Hulbult's and Danckwerts' sets of boundary conditions. Although Danckwerts' set of boundary conditions is more mathematically consistent than Hulbult's, the solution based on the latter is simplier. Besides, statistical analysis at the 0.01 level of significance showed that there is little to choose between the two in terms of accuracy. Also, the two solutions gave similar values of correlation coefficient, standard error, intercept and regressed slope.     

Simulating diffusion within soil aggregates: a simple model for cubic and other regularly shaped aggregates

Diffusion within a cube was simulated by a model which divides the cube into concentric volumes and computes by Fick's first law the diffusive flux between adjacent volumes and between the outermost volume and the external solution. The model can also be applied directly to a sphere and, with minor modifications, to other regular shapes. It was tested in two forms: (a) with the distances between the interfaces of adjacent concentric volumes made equal, and (b) with the volumes themselves equal, by using it to simulate the uptake of solute by a sphere from a stirred solution of limited volume. The output from the latter form of the model agreed the more closely with values obtained from a solution of the diffusion equations in radial co-ordinates, and this form was used subsequently. The model was used successfully to simulate the diffusion of bromide from cubes of chalk and chloride-36 from porous ceramic spheres, and its flexibility was illustrated by its ability to simulate experiments in which aliquots of the external solution were removed for assay.     

Thermal and Moisture Diffusion Properties of Amaranth Seeds

The physical characteristics, thermodynamic and transport properties of amaranth seeds relevant to the modelling and simulation of the drying processes of these seeds were studied. The water activity as a function of the temperature and moisture content was modelled by means of the Henderson's expression from water activity experimental data. The desorption–vaporisation heat was also calculated. From the solution to Fick's second law for a spherical geometry and assuming equilibrium conditions at the solid–gas interface, an effective diffusion coefficient was evaluated from experimental drying curves obtained in a moisture chamber. The effect of taking into account more than one term in the Fourier series solution was analysed and it is concluded that the diffusion coefficient corresponding to two terms in the series leads to better agreement with the experimental results for short times.     

基于驾驶员生物力学特性的拖拉机座椅位置参数优化

座椅为拖拉机与驾驶员的主要接触部件，其参数设计与优化对提高驾驶舒适性具有重要意义。基于此，该研究采用生物力学软件AnyBody建立驾驶员-驾驶环境生物力学耦合模型，并以小、中、大体型驾驶员为研究对象，以拖拉机座椅靠背倾角、水平距离及垂直高度为参数，以竖脊肌、多裂肌、腹直肌及腹外斜肌激活程度为评价指标，分析研究座椅位置参数对驾驶员腰部肌肉生物力学特性的影响规律，确定座椅最佳位置参数；其次以课题组研制的多自由度驾驶平台为基础，按照上述参数调节座椅位置，测试计算不同体型驾驶员腰部四个主要活动肌群的激活程度，并将测试结果与仿真分析结果进行对比，发现二者具有较好一致性，通过调整座椅参数能有效提升驾驶员腰部舒适性。对小体型驾驶员，当座椅靠背倾角为9.7°，水平距离为472.1 mm，垂直高度为465.3 mm时，4个肌群总的激活程度最低，驾驶员腰部舒适性最高；对中体型驾驶员，座椅最适靠背倾角为13.9°，水平距离为495.6 mm，垂直高度为485.3 mm；对大体型驾驶员，座椅最适靠背倾角为14.8°，水平距离为526.4 mm，垂直高度为520.7 mm。本文研究成果可为农机装备座椅位置参数优化提供一种新思路。     

土壤-水稻前茬离散元仿真参数标定及其旋耕轨迹分析

在进行稻油轮作区域水稻收获后旋耕作业中的前茬运动、受力仿真分析时,由于缺乏可靠的离散元仿真参数难以准确计算土壤-水稻前茬运动规律和相互间受力。该研究采用EDEM软件对土壤-水稻前茬混合物内部各物质的物理与接触参数进行离散元仿真标定。首先测定了土壤-水稻前茬混合物内各物质物理与相互间接触参数,以堆积角作为评价指标,利用仿真试验分析进行了显著因素筛选、最优水平取值范围确定及二阶回归模型下最佳参数寻优对参数进行了标定,得到土壤-水稻前茬混合物模型极显著参数的最优组合为土壤-土壤恢复系数0.407、土壤-土壤动摩擦系数0.123、土壤-水稻前茬静摩擦系数0.596、土壤表面能1.860 J,此时与试验堆积角误差为0.58%。并进行了土壤-水稻前茬间的直剪试验与仿真,得到了稳定后不同垂直应力下试验与仿真的直剪切应力误差分别为：5.4%（50 kPa）,4.1%（100 kPa）,3.1%（150 kPa）。最后在最优参数组合下,开展了基于MBD-DEM的旋耕土壤-水稻前茬轨迹分析试验,分析得到前茬跟随旋耕刀及直接被掩埋两种埋覆场景,仿真与土槽试验轨迹的Spearman秩相关系数分别为0.91,0.84,验证了仿真模型标定参数的准确性。研究结果可为水稻前茬旋耕轨迹调控过程的离散元仿真分析提供可靠的接触参数。     

油麦兼用型气送式集排器增压管气固两相流仿真与参数优化

为明确增压管结构对油麦兼用型气送式集排器分配均匀性的影响,该文运用DEM-CFD气固耦合方法仿真分析了波纹间距、凹窝深度和增压管长度对种子运动特性、分配均匀性和增压管气流场的影响,台架试验研究了增压管长度和气流压强对分配均匀性的影响.结果表明:增设增压管明显提高种子分布均匀度系数,降低种子速度和分配均匀性变异系数.速度流场分析表明增压管波峰与波谷的气流速度和压强交替变化,增压管中种子速度与受力呈现"正弦形"变化趋势.凹窝深度、波纹间距和增压管长度分别为4.2、15和180 mm时,种子分布均匀度系数和分配均匀性变异系数分别为91.17%和4.91%.台架试验表明,在优化结构参数组合下,排种油菜和小麦的气流压强分别为1200和1600 Pa时,分配均匀性变异系数分别达2.84%和2.89%.该研究为分析增压管中种子运动特性和优化其结构参数提供了参考.     

Measuring the diffusion coefficient of rhizosphere exudates in soil. I. The diffusion of non-sorbing compounds

A quick, convenient and robust method is presented for measuring the effective diffusion coefficients of non-sorbing solutes in soil. The method estimates the effective diffusion coefficient from a measured diffusion profile by optimizing the solution of a numerical simulation model describing the experimental system. The method was used to measure the effective diffusion coefficients of compounds found in root exudates.     

寒区沼气工程地下水源热泵加热系统能效分析

在北方寒冷地区,沼气工程加热系统如何能有效、合理地利用能源,提高能源利用率,是沼气工程实现低能耗,高产能必须解决的现实问题。该文依据地下水源热泵加热系统在沼气工程中应用的实例,建立了以?效率、热效率以及能级系数为评价准则的沼气工程加热系统能效分析模型,并通过对加热系统实际运行参数的测试,得到了沼气工程用户系统?效率为97.8%,地下水源热泵机组系统?效率为13.4%,沼气工程加热系统总的?效率为13.1%;加热系统总的热效率为85.3%;沼气工程用户耗热量的能级系数为0.161,用户供给热量的能级系数为0.164,地下水源热泵机组的能级系数为0.567。结果表明,对于沼气工程低品位热能用户,采用低温水供热科学合理;热泵机组系统回收了地下水中低品位热能,节约了高品位电能,加热系统能的数量有效利用程度较高;但热源与用户之间供需能质存在差异,在能质利用方面还需进一步完善。该结论可为今后沼气工程选择合理的加热模式提供参考依据。