产芝水库灌区农田水分转化及节水灌溉模式分析

在长期田间试验的基础上,建立了产芝水库灌区典型农田的土壤水分运动模型。结果表明,常规灌溉条件下灌区农田水分的无效渗漏量较大,降水和灌溉与土壤深层渗漏和农田蒸散量之间存在明显的正相关关系。基于作物的土壤水分调节标准,模拟得到灌区不同降水年型的节水灌溉模式,与常规灌溉相比,节水灌溉模式在丰水年可节省水240 mm,平水年140 mm,枯水年为90 mm,并且农田渗漏量显著低于常规灌溉,丰水年、平水年和枯水年的全年平均农田渗漏强度分别减少了0.66、0.35和0.27 mm/d。在作物关键生育期合理控制灌水量,能够保证作物正常需水的同时减少土壤水的无效渗漏,从而提高灌溉水的利用效率。     

双螺杆泵多点啮合型转子设计与内部流动特性

针对传统双螺杆泵螺杆转子螺旋面啮合区磨损严重、内泄漏大等问题,根据啮合原理,建立椭圆弧及其共轭曲线的啮合模型,构建传动比为2∶3的主从螺杆端面型线,提出一种新型多点啮合型螺杆转子结构.应用计算流体动力学方法对新型双螺杆泵内部流场进行数值计算,研究了泵内部流动特性.研究结果表明:所提出的新型螺杆转子在轴截面上可实现三点啮合,在双螺杆转子上形成多重密封;采用V形凹槽的主螺杆转子齿顶压力分布均匀,采用传统结构的从螺杆转子齿顶处压力分布呈阶梯状;从螺杆转子周向啮合间隙处泄漏速度为主螺杆转子的1.8倍,表明主螺杆转子齿顶V形凹槽两侧的光滑顶棱与泵腔内壁面形成的类迷宫密封可有效减小周向啮合间隙处的泄漏;新型螺杆转子较大改善转子的磨损适应性,有效减小了双螺杆泵的内泄漏,对提高双螺杆泵的高压环境适应能力具有重要意义.     

Bruise susceptibility of banana peel in relation to genotype and post-climacteric storage conditions

The aim of this study was to understand the genotypic factors and post-climacteric storage conditions that affect bruise susceptibility of banana peel. Putative physicochemical indicators of bruise susceptibility, including peel electrolyte leakage (PEL), total polyphenolic content, hardness, water content, and peel thickness, were investigated. Bruise susceptibility is the lowest impact energy needed to produce visible bruising by an object dropped on post-climacteric banana fruit from a pre-determined height, converted into impact energy (20–200 mJ with a 20 mJ increment). The bananas were stored either at 18 °C throughout ripening or at 13 °C between the 2nd and 6th day after ethylene induction. Five cultivars with contrasting susceptibility to impact bruises were used. Neither Grande Naine nor hybrid Flhorban925 bruised at the maximum impact energy (200 mJ) during ripening whatever the storage conditions. A gradient in bruise susceptibility was observed among the other cultivars: French Corne > Fougamou > hybrid Flhorban916. Bruise susceptibility increased during ripening and was higher in bananas stored at 18 °C. The lower ripening temperature resulted in a two-day delay to fruit maturity as well as in bruise susceptibility. Bruise susceptibility was positively correlated with PEL (R = 0.78) and to a lesser extent negatively correlated with hardness (R = −0.45), and was not correlated with polyphenolic content. In conclusion, membrane permeability provides the first clue to understanding bruise susceptibility.     

Drivers of soil erosion and subsurface loss by soil leakage during karst rocky desertification in SW China

As an extreme manifestation of environmental degradation, karst rock desertification is caused by soil loss and rock exposure. In some areas with serious rocky desertification, there is no soil to be eroded or leaked. The soil loss in these areas superimposes soil erosion and unique subsurface loss by soil leakage through fissures, pipelines, sinkholes, etc., which directly reduce soil resources and accelerate rocky desertification. However, the factors driving soil erosion and subsurface loss by soil leakage are still unclear. Rainfall experiments were conducted on simulated slopes with surface-exposed bedrock and subsurface fissures based on field investigations in a karst rocky desertification area of Guizhou Province, China. Four factors, including rainfall intensity, slope gradient, bedrock exposure rate and subsurface fissure degree, were considered in the experiment. We found that the amount of soil surface erosion and subsurface leakage loss is driven not only by the runoff volume but also by other influential factors. Rainfall intensity is the driving factor determining the amount of surface erosion and subsurface leakage loss of soil and water and the relationship between them. The slope gradient plays a leading role only in subsurface fissure flow leakage loss. The bedrock exposure rate drives the surface soil erosion rate, shows a critical value (30%), and dominates the fissure flow leakage loss rate. Subsurface fissure density plays an important role in the surface loss of soil and water; however, an increase in the subsurface fissure density does not obviously accelerate the subsurface leakage loss of soil and water. Although this result, obtained from laboratory simulations, may differ at the field scale or larger, it could provide a foundation for systematic studies on soil erosion/leakage and insights into the relations between rocky desertification and soil erosion/leakage and their driving factors in karst rocky desertification.     

便携式顶空-气相色谱质谱联用仪测定土壤中四氢噻吩

四氢噻吩常用作燃气的气味添加剂,用以追踪燃气的泄露。为建立一套便携式顶空-气相色谱质谱联用法(HS-GC/MS)检测土壤中四氢噻吩浓度的方法,采用正交试验对顶空进样条件(平衡温度、平衡时间和进样压力)和气相色谱质谱检测条件进优化。结果表明,顶空进样的最佳条件为平衡温度80 ℃,平衡时间20 min,进样压力100 kPa。便携式气相色谱质谱联用法(GC/MS)的升温程序：初始柱温60 ℃,保持2 min,以10 ℃/min的速率升至90 ℃,保持4 min,然后以20 ℃/min的速率升至200 ℃,保持10 min。在最佳条件下,方法的检出范围0.005 mg/kg～10.000 mg/kg,不同浓度四氢噻吩的加标回收率为82.4%～98.5%,日内和日间精密度相对标准偏差为4.6%～7.5%,建立的方法快速高效、重复性好,可用于土壤中四氢噻吩现场快速检测。     

降水影响冬小麦灌溉农田水分渗漏和氮淋失模拟分析

为了研究降水对根层 (1.2m)水分渗漏和氮淋失的影响 ,采用Hydrus 1D模型模拟近 30年实际气候条件下京郊冬小麦田的水氮运移过程。结果表明 ,传统水肥管理 (灌溉量 2 70mm ,施氮量 15 0kg·hm-2 )冬小麦农田 ,降水量小于 5 0mm时 ,水分渗漏量均值为 5 .0mm ;降水量在 5 0～ 10 0mm ,对应水分渗漏量均值为 2 3.6mm ;当降水量为10 0～ 15 0mm或大于 15 0mm时 ,平均水分渗漏量为 36 .9或 12 5 .6mm。对应的氮淋失量分别为 1.5、5 .8、9.6和 4 0 .4kg·hm-2 。水分渗漏及氮淋失主要发生在冬小麦返青期和拔节期灌溉后 ,因此应减少早期灌溉量并应避免过早施肥。水分渗漏量可表示为降水指数的指数函数 ,而氮淋失量则与水分渗漏量呈线性相关。在可预测降水条件下 ,文中给出的经验关系式可用于估测水分渗漏量和氮淋失量。