荷电喷雾电晕电极诱导电场数值计算与分析

为深入研究电晕荷电喷雾产生电场的分布情况,针对电晕荷电喷雾中常用的多针组合式电极,采用电荷模拟法,运用matlab软件编程,对电极诱导电场进行数值计算,得出了电场中任意点的电势、场强值及其分布图。通过计算分析发现,电晕放电产生的静电场是极不均匀的;场强由电极结构参数-极径、电极尖端曲率半径、电极电压、针状电极的个数以及电极环中心距地面的垂直高度决定;雾滴从喷嘴到靶标的输运过程中,电晕电极产生的电场仅在输运初始阶段对雾滴的运动起主导作用。     

均质充量压燃式发动机柴油混合气制备方法的研究

研究了一种新概念发动机-均质充量压燃式(HCCI)发动机.其气缸内燃烧温度低而均匀,产生的氮氧化物(NOx)非常低,其碳烟(PM)排放也很低,兼有高效率和低污染的优点.尽管均质充量压燃式发动机具有很大优点,但均质混合气的制备是阻碍其实用化的关键问题之一.为此,在总结前人研究成果的基础上,设计开发了一种用于HCCI发动机的液体燃料均质混合气制备方法.该方法是利用发动机排出废气的热量和进、排气管的复合结构实现的.     

Nitrate leaching in a silage maize field under different irrigation and nitrogen fertilizer rates

Quantification of the interactive effects of nitrogen (N) and water on nitrate (NO₃) loss provides an important insight for more effective N and water management. The goal of this study was to evaluate the effect of different irrigation and nitrogen fertilizer levels on nitrate-nitrogen (NO₃-N) leaching in a silage maize field. The experiment included four irrigation levels (0.7, 0.85, 1.0, and 1.13 of soil moisture depletion, SMD) and three N fertilization levels (0, 142, and 189 kg N ha⁻¹), with three replications. Ceramic suction cups were used to extract soil solution at 30 and 60 cm soil depths for all 36 experimental plots. Soil NO₃-N content of 0-30 and 30-60-cm layers were evaluated at planting and harvest maturity. Total N uptake (NU) by the crop was also determined. Maximum NO₃-N leaching out of the 60-cm soil layer was 8.43 kg N ha⁻¹, for the 142 kg N ha⁻¹ and over irrigation (1.13 SMD) treatment. The minimum and maximum seasonal average NO₃ concentration at the 60 cm depth was 46 and 138 mg l⁻¹, respectively. Based on our findings, it is possible to control NO₃ leaching out of the root zone during the growing season with a proper combination of irrigation and fertilizer management.     

静电喷雾技术的基础研究

液体荷电雾化技术能够有效降低雾化的粘滞阻力,提高雾化效果。为此,从理论方面分析了影响液滴雾化和雾滴荷电的参数以及影响荷质比的因数,并列举了静电技术在农业上的应用;着重阐述了静电喷雾技术在农业方面的应用前景。     

甲醇缸内直喷发动机均质燃烧特性研

在一台四缸柴油机改造的火花点火甲醇缸内直喷发动机上,高负荷时,在进气冲程将燃油喷入缸内,形成近化学计量比的混合气来实现均质燃烧.通过对典型工况的气缸压力的测量和分析,探讨了不同参数对甲醇发动机燃烧特性的影响.结果表明:甲醇缸内直喷发动机最大功率和最大扭矩比原机分别提高5.88%和20.90%,发动机最高热效率可达35.3%,远高于普通汽油机水平.甲醇缸内直喷发动机的滞燃期和急燃期随负荷的增加而变小.全负荷时,甲醇发动机的燃烧放热始点随转速的增大而推迟,滞燃期和急燃期随转速的增大而增加.发动机循环变动随工况的变化规律与滞燃期一致.     

西南山地丘陵区永久性基本农田的多目标决策划定方法

为科学地引导西南山地丘陵区永久性基本农田的划定,该文以重庆市垫江县为例,通过层次分析法、熵权系数法、TOPSIS法（technique for order preference by similarity to an ideal solution）和约束因子建立决策模型体系,结果表明：耕地指标中灌溉保证率、平均降雨量、交通和农村居民点辐射的自身优势突出。土壤质量各指标平均值（介于0.2～0.75之间）、标准差（介于0.09～0.3之间）、变异系数（介于13～75之间）为中等以下水平。自然条件中,灌溉保证率和耕地连片性的综合权重最大,大于10℃积温和平均降雨量的综合权重最小、且指标值的区间变化最大;土壤质量中,有机碳在层次分析法下权重最大;距离条件中,入选耕地受城镇的辐射作用明显、区位优势突出。耕地在入选重要程度上,依次排序前4位的是灌溉保证率、耕地连片性、城镇的辐射和土壤有机碳,测度和贴近度显示,地块间优劣接近,距离条件整体较优。耕地的入选从贴近度等级划分为：重点型、适宜型、调控型、后备型,约束条件下调出的地块为优势耕地（即重点型和适宜型）。最终划定成果显示适宜型和调控型比例增大,重点型和后备型比例减小。并利用数据验证了该决策模型体系的合理性、规范化和可行性。     

Soils and land use in the Tigray highlands (Northern Ethiopia)

Land use in a 208 ha representative catchment in the Tigray Highlands, Dogu'a Tembien district in Northern Ethiopia was studied in relation to soil geography. Typical soils are Vertisols, Vertic Cambisols, Cumulic Regosols, Calcaric Regosols and Phaeozems. Patterns of land use vary greatly within the catchment and results from χ²‐tests showed strong associations (p < 0·001) between soil type and land use and crop production system. There is a strong association between cropland and colluvium high in basaltic content because the most fertile soils, such as Vertisols and Vertic Cambisols, have developed on this material. Preference is for autochthonous soils on in situ parent material, irrespective of the rock type, to be put under rangeland. Land use by smallholders in Dogu'a Tembien appears to be the result primarily of the interaction between environmental and social factors. Copyright © 2007 John Wiley & Sons, Ltd.     

电动拖拉机PC-DSPM电机电子变极策略与分析

针对田间作业和转场运输等不同工况时的行驶速度需求,该研究提出使用双凸极变极永磁（pole-changing doubly-salient permanent magnet,PC-DSPM）电机作为电动拖拉机的驱动电机,通过变极获得驱动电机的多种机械特性。基于气隙磁场调制理论,将PC-DSPM电机气隙磁场中的主要工作谐波分为2组,采用电子变极改变电枢绕组连接方式,从而选择不同组别的气隙磁场谐波参与机电能量转换,形成PC-DSPM电机3种运行模式。根据不同模式下的转矩-转速曲线,选取电机在恒功率区的2个变极切换点,并据此将拖拉机的运行速度划分为0～7.7、7.7～10.5和10.5～32.7 km/h共3个区间。为实现平滑变极,构建自抗扰控制和跟踪微分器的PC-DSPM电机变极策略。与采用自抗扰控制的阶跃响应变极相比,虽然2个切换点处的变极时间分别延长至400和600 ms,但变极过程中dq轴电流过渡平稳,转矩波动分别下降8.5%和11.8%,转速恒定在920和1 250 r/min。研究结果可为实现电动拖拉机多工况高效运行及变极永磁电机平滑切换提供理论参考。     

基于坡度的黑土区切沟密度协同克里格插值方法研究

切沟侵蚀已成为东北黑土区土壤侵蚀的重要组成部分。结合野外样区实地调查切沟分布数据与空间插值方法是快速获取大面积切沟密度值的有效手段。流域的平均坡度值是切沟形成的影响因素之一,为提高切沟密度值空间分布的插值精度,在黑龙江省海伦市内,利用网格法均匀选取40个1 km²左右的小流域,在实地测量区域内切沟密度数据的基础上,应用距离权重反比法、普通克立格和以小流域的平均坡度作为协同变量的协同克立格对其做空间插值。结果表明:切沟密度与协同区域化变量受结构性因素的影响远大于随机性因素,均为强空间自相关性;距离权重反比法与普通克里格法的预测精度相近;协同区域化变量的空间结构性优于单一变量,协同克立格法生成的空间分布图精细度明显提高,均方根误差降低20%以上,预测值与实测值的相关系数提高89%以上,协同克里格可有效提高区域切沟插值精度。     

Sulfate and Calcium Movement in an Allophanic Soil—The Relevance of Ion‐Pair Adsorption in the Soil–Plant System

Cooperative adsorption involving anions and cations, termed ion‐pair adsorption (IPA), is reported to increase the retention of some ions in certain soils. Sulfate and calcium can exhibit such interaction, and this affects their movement through the soil. Ion‐pair adsorption is shown here in miscible displacement experiments with a variable‐charge soil. The relevance of IPA under more realistic conditions is further investigated in a pot experiment. Rapeseed (Brassica napus) was grown at two different irrigation regimes and with two sulfur fertilizer sources. Calcium sulfate (CaSO₄·2H₂O) was used to induce IPA in contrast to potassium sulfate (K₂SO₄). The results suggest that IPA reduces sulfate and calcium leaching only in the short term. Continued irrigation dissipates the differences between the two fertilizer sources. Final soil ion concentrations and the plant uptake could not be related to IPA, evidencing the short‐term relevance of IPA. The influence of IPA on the bioavailability of calcium and sulfate to plants still demands further study.