基于EDEM的双排型孔轮式油菜排种器的排种性能分析

基于离散单元法和EDEM软件,建立了双排型孔轮式油菜排种器的离散元模型,对不同排种轴转速下种群扰动强度进行分析,研究排种轴转速和不同排型孔对排种器排种量和排种均匀性变异系数的影响。结果表明:当排种轴转速为30～90r/min时,单独使用第一排型孔排种,排种均匀性变异系数为42.75%～54.17%,单独使用第二排型孔排种,排种均匀性变异系数为38.46%～44.1%;排种器使用双排型孔同时排种,排种均匀性变异系数为28.2%～40.1%,双排型孔工作较单排型孔工作排种均匀性提高。该排种器种子充入型孔的极限转速为60 r/min,当转速为0～60 r/min时,单位时间的排种量呈线性变化,当排种器转速超过极限转速时,单位时间的排量相对减小。     

基于电池状态的车载铅酸电池输出在线控制方法

针对车载铅酸电池长时间以较大电流放电导致蓄电池实际容量快速下降,造成寿命短的问题,提出了一种基于电池状态的车载铅酸电池输出在线控制方法。首先通过实验建立放电过程蓄电池当量电阻和SOC(State of charge,荷电状态)之间的关系,进而得到蓄电池放电电流和输出功率之间的关系;接着通过实验建立蓄电池SOH(State of health,健康状态)、放电电流以及充放电循环次数之间的关系,进而得到每个阶段考虑寿命的最大放电电流计算方法;最后通过仿真实验验证,该控制方法能延长车载铅酸电池寿命。     

液化乙烷船液罐装载极限的提高方法

为了优化液化乙烷船远洋运输能力,根据液化气船液罐装载极限的基本要求和液化乙烷的货品属性,从提高基准温度下货物的对应密度和充装极限两个方面研究了提高液化乙烷船液罐装载极限的方法。将理论计算与液化乙烷船实际数据相结合,分析了BOG的不同回收利用方式对控制乙烷密度的影响;为了使主罐体充装极限达到99.5%,在液罐顶部设置气室,并将液罐压力释放阀安装于气室顶部;同时,对液位测量、温度测量、再液化设备启动压力设定、应急切断响应周期、液罐尺寸等修正裕量系数开展了研究,得出了在满足约束条件下提高装载极限的方法。结果表明:该方法可使得液化乙烷在基准温度下的对应密度、充装极限分别提高6.67%～8.89%、1.5%,可在其他液化乙烷船储运中推广应用。     

Repeated drying–rewetting cycles and their effects on the emission of CO2, N2O,NO, and CH4 in a forest soil

Prolonged summer droughts due to climate change are expected for this century, but little is known about the effects of drying and wetting on biogenic trace‐gas fluxes of forest soils. Here, the response of CO₂, N₂O, NO, and CH₄ fluxes from temperate forest soils towards drying–wetting events has been investigated, using undisturbed soil columns from a Norway spruce forest in the “Fichtelgebirge”, Germany. Two different types of soil columns have been used for this study to quantify the contribution of organic and mineral horizons to the total fluxes: (1) organic horizons (O) and (2) organic and mineral soil horizons (O+M). Three drying–wetting treatments with different rewetting intensities (8, 20, and 50 mm of irrigation d^–1) have been compared to a constantly moist control to estimate the influence of rainfall intensity under identical drying conditions and constant temperature (+15°C). Drought significantly reduced CO₂, N₂O, and NO fluxes in most cycles. Following rewetting, CO₂ fluxes quickly recovered back to control level in the O columns but remained significantly reduced in the O+M columns with total CO₂ fluxes from the drying–wetting treatment ranging approx. 80% of control fluxes. Fluxes of N₂O and NO remained significantly reduced in both O and O+M columns even after rewetting, with cumulative fluxes from drying–wetting treatments ranging between 20% and 90% of the control fluxes, depending on gas and cycle. Fluxes of CH₄ were small in all treatments and seem to play no significant role in this soil. No evidence for the release of additional gas fluxes due to drying–wetting was found. The intensity of rewetting had no significant effect on the CO₂, N₂O, NO, and CH₄ fluxes, suggesting that the length of the drought period is more important for the emission of these gases. We can therefore not confirm earlier findings that fluxes of CO₂, N₂O, and NO during wetting of dry soil exceed the fluxes of constantly moist soil.     

Effect of freezing and thawing processes on some physical properties of saline–sodic soils mixed with sewage sludge or fly ash

Dispersion of saline–sodic soils was rather difficult to leach. Therefore, negative effects of freeze–thaw on soil physical properties should be reduced by inexpensive and practical methods. This study investigates the effect of freeze–thaw cycles (3, 6, and 9) on wet aggregate stability, bulk density, and permeability coefficient in three soils with different electrical conductivity and exchangeable sodium percentage levels (soil I: 5.30 dS m⁻¹, 47.51%; soil II: 42.80 dS m⁻¹, 55.45%; soil III: 36.30 dS m⁻¹, 59.34%) which consist of different proportions of sewage sludge and fly ash by volume (10%, 20%, and 30%). The experiment was conducted under laboratory conditions using disturbed and non-cropped soil samples mixed with sewage sludge and fly ash. Soils mixed with sewage sludge produced higher aggregate stability and permeability coefficients and lower bulk density values as compared to the soils mixed with fly ash. Sewage sludge added with a rate of 30% eliminated the negative effects of freeze–thaw processes on wet aggregate stability. Freeze–thaw processes did not affect the bulk density of the soils II and III, which were mixed with sewage sludge. However, fly ash addition decreased the bulk density of these soils very significantly after nine freeze–thaw cycles. Addition of sewage sludge or fly ash with rates of 20% and 30% significantly increased the permeability coefficients in soil I after nine freeze–thaw cycles. Results indicated that addition of sewage sludge and/or fly ash to saline–sodic soils could be alternative way for reducing negative effects of freezing–thawing on soil wet aggregate stability, bulk density, and permeability coefficient.     

土壤冻融交替生态效应研究进展

土壤冻融作用是高纬度和高海拔地带性土壤热量动态的一种表现形式.国际上关于冻融的研究多集中在北方高纬度地带,特别是苔原、泰加林和北极生态系统,越来越集中在全球变化对冻融生态系统土壤过程的效应方面.已有研究表明冻融作用会引起土壤团聚结构破坏并导致冻融侵蚀、土壤溶液中养分浓度升高而导致土壤养分流失、土壤解冻后还可能导致土壤呼吸和N素矿化以及一些痕量气体短时间释放增加等,这些研究表明了冻融过程对土壤物理、化学、生物等各方面的效应.我国有大面积北方季节性地带冻土和青藏高原高海拔冻土,而在土壤冻融作用及生态效应方面的工作较少,值得关注和深入研究.     

Soil loss tolerance limits for planning of soil conservation measures in Shivalik–Himalayan region of India

Soil loss tolerance limit is defined as the threshold upper limit of soil erosion that can be allowed without degrading long term productivity of specific soils. In India a default soil loss tolerance limit (SLTL) of 11.2 Mg ha^− 1 yr^− 1 is followed for planning soil conservation activities. The objective of this investigation is to provide a methodology to estimate quantitative SLTL for the Shivalik–Himalayan region in India for suggesting suitable soil conservation measures. A quantitative model was used to integrate potential soil indicators such as infiltration rate, bulk density, water stable aggregate, organic carbon and fertility status to assess soil quality governing soil resistibility to erosion. Scaling functions were used to convert soil parameters to unit less 0 to 1 scale. Normalized values of soil parameters were then multiplied by assigned weights based on relative importance and sensitivity analysis of each indicator. Soils were grouped into 1, 2 and 3 depending on overall additive score. A general guideline developed by the USDA-Natural Resource Conservation Service (NRCS) was followed with certain modifications in depth category for estimation of SLTLs. Soil loss tolerance limits varied from 2.5 to 12.5 Mg ha^− 1 yr ^− 1 compared to single value of 11.2 Mg ha^− 1 yr ^− 1 being followed earlier. Consideration of the newly estimated SLTLs would facilitate site specific conservation planning and prioritising areas for watershed management activities in India.     

根系分区交替灌溉对温室甜椒不同灌水下限的响应

依据2006、2007年两年小区试验,对根系分区交替灌溉条件下温室甜椒生长、产量及水分利用效率对不同灌水下限的响应进行了研究.结果表明:占田间持水量60%的灌水下限(T3)处理甜椒叶片光合速率最大,有效地阻止无效蒸腾失水,水分利用效率最高,占田间持水量70%的灌水下限(T4)处理产量达到最高.对甜椒产量、水分利用效率与灌水下限之间的关系进行回归分析,得出30 cm内当灌水下限为田间持水量的70%左右时,甜椒鲜质量小区产量可达最大值;当灌水下限为田间持水量的65%时,甜椒水分利用效率有最大值.综合考虑节水、增产和提高水分利用效率等多种因素,根系分区交替灌溉条件下温室甜椒灌水下限应控制在65%田间持水量左右为宜.     

基于区间线性规划理论的水稻土重金属Cd形态限量标准研究

应用生态环境效应法,借助区间线性规划理论,以稻谷Cd与活性形态(可交换态、碳酸盐结合态、铁锰氧化物结合态和有机物结合态)Cd含量间的线性回归模拟方程为目标函数,以稻谷Cd限量卫生标准为限制条件,筛选各约束条件下的最大最优值为各活性形态Cd含量的限量标准,为成都平原土壤重金属污染控制提供参考,为深入研究基于生物有效性的土壤重金属限量标准的制定提供科学依据。结果表明,土壤Cd活性形态限量标准分别为:可交换态Cd≤0.0865 mg/kg,碳酸盐结合态Cd≤0.2641 mg/kg,铁锰氧化物结合态Cd≤0.2461 mg/kg,有机物结合态Cd≤0.0760 mg/kg。     

考虑径流非一致性的水库分期旱限水位优化研究

【目的】分析变化环境下水文序列的非一致性,为龙羊峡水库分期旱限水位优化调度模型的建立提供参考。【方法】采用Mann-Kendall检验法、有序聚类分析法和水文序列振动中心重构法,对龙羊峡水库年径流序列进行一致性分析及修正,然后利用水库旱限水位分级和Fisher最优分割法,对径流序列修正前后不同干旱等级下的水库分期旱限水位进行确定,最后通过耦合分期旱限水位建立以缺水指数最小为目标函数的龙羊峡水库优化调度模型,对径流序列修正前后两种情况下的分期旱限水位进行对比研究。【结果】一致性检验发现,龙羊峡水库径流序列具有明显下降的趋势,并在1989年发生突变。经一致性修正后计算龙羊峡水库7-10月、11-12月、1-4月、5-6月4个分期的旱限水位,在轻旱条件下分别为2 530.00,2 534.91,2 539.10和2 535.13 m,中旱条件下分别为2 530.00,2 535.44,2 539.80和2 536.70 m,重旱条件下分别为2 530.00,2 535.87,2 540.35和2 537.89 m;特旱条件下分别为2 530.00,2 536.06,2 540.58和2 538.12 m。采用不同调度模型对龙羊峡水库进行优化调度,结果显示修正后的调度效果较好,其总缺水量、缺水指数相比修正前分别降低5.37%和6.03%,其中枯水时段平均缺水量降低了10.71%,缺水程度改善明显。【结论】非一致性径流对龙羊峡水库旱限水位的确定有一定影响,一致性修正后的径流使水库旱限水位的确定更加可靠,水库的抗旱能力得以提升,可为水库供水、抗旱应急管理决策提供参考。