SYNERGETIC EFFECTS OF SILANE-GRAFTING AND EVA ON WATER TREE RESISTANCE OF LDPE

The synergetic influence of silane-grafting and polar additives （EVA） on the water tree resistance of the low density polyethylene has been investigated. A series of samples obtained before and after hydration have been characterized by measuring gel content, infrared spectroscopy （FTIR）, differential scanning calorimetry （DSC） and dielectric measurements. The results obtained clearly show that the silane condensation occurred and that the silane-grafting and polar additives have synergetic effects on the water tree resistance of LDPE with little influence on its dielectric properties, e.g. the dielectric breakdown strength, dielectric permittivity and loss tangent.

Capacitance of Water Tree Modeling in Underground Cables

Water Tree is a corrosion phenomenon in cross-link polyethylene (XLPE) insulation. It is commonly found in underground cables. Water tree induced fault is difficult to detect due to its high impedance and difficult to model due to its random nature. In recent years, underground cables have become more popular in the power industry. They are resistant to environmental damage and has reduced space requirement. They are suitable to areas with high environment hazard or heavily populated areas where space is a constraining factor. As a result, studying and modeling the structure and effect of water tree become increasingly important. Since majority of the fault inducing water trees are vented trees which originated from the surface of the cable insulation, the mathematical model focuses on this particular type of water tree. To reduce the complexity of the model, the shape of the water tree afflicted region of the insulation is assumed to be ellipsoidal and the permittivity of the region is assumed to be linearly changing. Finite element analysis is used to analyze the water tree affected region. The resultant capacitance is calculated and compared with a physical model from Comsol. The result obtained using the proposed mathematical model and the result obtained using physical simulation through Comsol package agrees with each other. Hence, this method can be used to analyze the effect of water tree fault in large power systems.

Nonlinear Response Analysis for Insulation Diagnosis of Water-tree Aged 10 kV XLPE Cable Using Pulse Voltage

The diagnosis of water trees of cable insulation is of great importance as the water-treeing is a primary cause of aging breakdown for the middle voltage cables. In this paper, it is described how the water-tree-aged 10 kV XLPE cables were diagnosed. The cables were subjected to electrical stress of 5.9 kV/mm and a thermal load cycle in a curved water-filled tube for 3, 6 and 12 months of aging in accor- dance with the accelerated water-tree test method. The aged cables were used as the samples for water-tree diagnosis. First, the water-tree degraded cable, was charged by a DC voltage, and then the cable was grounded while a pulse voltage was applied to it for releasing the space charge trapped in the water trees. The amount of the space charge, which corresponds to the deterioration degree of the water trees, was calculated. The effects of DC voltage amplitude, pulse voltage repetition rate and aging conditions on the amount of the space charge were studied. Obtained results show that the amount of the space charge has a positive correlation with the applied DC voltage and the ag- ing time of the cables, and that a peak value of space charge appears with the increase of the pulse voltage repetition rate. An optimum pulse voltage repetition rate under which the space charge can be released rapidly is obtained. Furthermore, the releasing mechanism of space charge by the pulse voltage is discussed. Accumulated results show that the presented method has a high resolution for the diagnosis of water tree degradation degree and is expected to be applied in practice in future.

Impacts of Water-Tree Fault on Ferroresonance in Underground Cables

Nowadays, more and more electrical power is being distributed to customers by underground cables rather than overhead transmission lines due to their advantage of providing better protection in inclement weather. They also have significantly reduced electromagnetic field emission because of their copper shielding. But underground cables have larger capacitance than transmission lines per unit. Thus, ferroresonance is more likely to occur in distribution systems using underground cables. Moreover, soil humidity at a depth of one meter remains 100 percent for most of the year, a factor that risks the occurrence of water tree (WT) in cables. Consequently, both ferroresonance and WT are prone to occur in underground cable systems. The objective of this paper is to determine the relationship between ferroresonance and water tree. A test system was designed to simulate and analyze ferroresonance in a cable system caused by single-phase switch and water tree. Eight scenarios of water tree were compared in the simulation. There sponses of ferroresonance are presented in this paper and two common patterns are observed from the simulation results.

Managing irrigation of fruit trees using plant water status

Optimum growth and production of fruit crops is strongly linked to managing irrigation water. Various method of estimating tree water requirements have been utilized such as direct and indirect soil, water, and climatic measurements. Due to differences in fruit tree anatomical and morphological structures and their adaptation to excess and deficit soil water content, such estimates of irrigation water requirements may be more suitable for herbaceous plants but not as accurate for trees. Studies on temperate and tropical fruit trees, using apple (Malus domestica) and star-fruit (Averrhoa carambola), respectively, showed that tree water potential is highly correlated to soil water status. Irrigation based on climate data (ET) and monitoring of soil water resulted in no significant differences in soil or tree water status of orchard-grown fruit trees under temperate and subtropical climatic conditions. The results indicated the need for better understanding and utilization of tree physiological parameters for management of irrigation water of fruit crops. This will ultimately lead to achieving optimum yield and fruit quality while conserving water resources.

A Comparative Study of Water Imagery in the Chinese Poem Happy Rain on a Spring Night and American Poem A Drop Fell on the Apple Tree

This essay directs at the water imagery of two poems Happy Rain on a Spring Night and A Drop Fell on the Apple Tree.Although living in different time and place, Chinese poet Du Fu and American poetess Emily Dickinson share some deep understanding of the water. This secret of water imagery is unveiled in this essay with the help of Archetypal Criticism, revealing its significance to the human beings as a race.

Using Nonconventional Water in Irrigation of Olive Trees and Its Effect on Olive Oil Properties

The response of olive orchard with same age and type to irrigation with treated municipal wastewater and freshwater was investigated in three years. Physical and chemical properties of the treated municipal wastewater reuse in agriculture (the effluent) produced by the Sheikh Ejleen wastewater treatment plant in Gaza Strip, freshwater, soil, and olive oil were determined and compared with Palestinian and international standards. The biological oxygen?demand (BOD) of Sheikh Ejleen effluent is 60 mg·l-1, which indicates low quality effluent. The results indicate that most of olive oil quality parameters—including heavy metals and trace elements for both fruits irrigated with treated wastewater or irrigated with freshwater—fall within the acceptable standard limit values. Moreover, soil analysis shows that organic content and cation exchange capacity were improved in soil irrigated with treated wastewater in comparison with that irrigated with freshwater. The results also show that there is no trace elements or heavy metals accumulation in soil.

Effects of Different Water and Fertilizer Combinations on Tree Structure,Leaf Parameters and Photosynthesis of Apple Saplings

[ Objective] This study aimed to investigate the effects of different water and fertilizer combinations on apple saplings. [ Method] ＇ Tianhong 2＇ Fuji /SH40/Malus robusta Rehd. was used as the experimental material to analyze the effects of different irrigation modes and combinations of basal fertilizer and dressing fertilizer on tree structure, leaf parameters and photosynthesis of apple saplings. [ Result] The results showed that different water and fertilizer combinations ex- hibited varying effects on tree structure, leaf parameters and photosynthesis of apple saplings. To be specific, applying 432 000 kg/hm2 basal fertilizer, 480 kg/hm2 urea and 915 kg/hmz organic fertilizer ＋ 0 ＋ 915 kg/hm2 organic fertilizer as dressing fertilizer, and 1% urea as leaf fertilizer was conducive to promoting growth of branches and leaves, increasing leaf thickness, individual leaf area and SPAD, and improving photosynthesis of apple saplings under half root irrigation and whole root irrigation conditions. In addition, the effects were more significant under whole root irrigation conditions. [ Conclusion] Selecting the appropriate water and fertilizer combination is conducive to the growth of apple saplings.

Effects of Hydrogels on Tree Seedling Performance in Temperate Soils before and after Water Stress

Super Absorbent Polyacrylate (SAP) hydrogels absorb and store water thereby aiding plant establishment when incurporated in the soil. The effect of cross-linked SAP hydrogel amendment on the performance of tree seedlings of Picea abies, Pinus sylivestris and Fagus sylvatica grown in temperate soils under water stress and non-water stress periods was investigated in a green house. The objective was to compare the root and shoot biomass of seedlings of the three species grown in sand, loam and clay soils amended with 0.4% w/w hydrogel in non water stress conditions as well as survival, root and shoot biomass after subjection to water stress. The seedlings were grown for 16 weeks, harvested and shoot as well as root biomass determined before water stress. The seedlings were also subjected to water stress and their biomass assessed at death following the water stress. The results showed that root and shoot biomass were generally higher in hydrogel amended soils compared to the controls. Root and shoot biomass of Fagus sylvatica was lower compared to Picea abies and Pinus sylivestris before water stress. The 0.4% hydrogel amendment significantly increased species’ survival in the different soils studied. Although root biomass was higher in hydrogel amended sandy soil compared to other soils, P. sylivestris and F. sylvatica shoot biomass were higher in hydrogel amended clay and loam soils compared to the sandy soil after water stress. Biomass was higher in sand compared to loam and clay soils under non-water and water stressed conditions. Since SAP hydrogel amendment improved the survival and biomass production of tree seedlings before and after water stress, use of SAPs could be promoted to enhance seedling production in water stress and non-water stress environments.

Short Term Leguminous Trees-Tillage Interactions and Their Effect on Soil-Water Content in a Semi-Arid Agroforestry Parkland

Agricultural activities that encourage slashing, burning and ploughing greatly affect the soil structure and soil organic matter on which soil water retention depends. In this study, we hypothesized that inclusion of rotational leguminous tree species improves soil water retention in a semi-arid conservation agriculture system. In a study done in Kibwezi, semi-arid eastern Kenya, results showed that the amount of water retained in the different soil strata from plots with different tree species and tillage practices was highly significant (P = 0.032). Plots with planting basins and Gliricidia sepium and Faidherbia albida tree species retained more water in both the upper and lower strata. Plots with G. sepium tree species under planting basins and zero tillage under F. albida had significantly higher soil organic carbon levels than plots that were managed under ridges and ploughing (P = 0.002). On the other hand, bulk density in plots with planting basins and zero tillage and ridges ranged between 1.35 g/cm3 and 1.53 g/cm3. Conventional tillage plots had bulk density values of 1.65 g/cm3 and 1.72 g/cm3 in the upper and lower strata respectively. The time-dependent nature of rotational leguminous tree species on soil organic matter and soil water retention in the semi-arid conservation agriculture system highlights the importance of considering these species for improving organic carbon and water retention for improved crop production.

Reduction in Water Stress for Tree Saplings Using Hydrogels in Soil

The effect of soil amendment with hydrogel on reducing water stress was tested for Siberian elm (Ulmus pumila) and silver maple (Acer saccharinum) saplings. The trees were planted in soils with one of two concentrations of hydrogel (0.5% or 1% dry weight) as compared to the control soil (0% of hydrogel) and watered either daily, weekly, or bi-weekly. Growth was monitored by measuring height and stem diameter. Stress was monitored by measuring SPAD readings and normalized difference vegetation index (NDVI), as proxy measures of chlorophyll content and photosynthetic activity, respectively. Water stress decreased NDVI (p < 0.05) but did not have a significant effect on SPAD readings. Soil with 0.5% concentration of hydrogel was positively associated with greater height and NDVI (p < 0.01) for both maple and elm trees. Hydrogels had a species-specific effect on SPAD readings. The interaction between hydrogel concentration and the watering regime had a significant effect on the height and NDVI (p < 0.01) of elms, but not maples. The improved performance of water-stressed tree saplings in hydrogel-amended soils was presumably due to the ability of hydrogels to absorb and then gradually release water and nutrients. This is of special interest for urban foresters, because water stress and nutrient deficiency are two important growth-limiting factors for street trees.

森林火灾中使用细水雾进行灭火仿真方法研究

森林火灾作为一种极具危害性的自然灾害,其发生和蔓延过程通常受到气候、地形、植被、可燃物等多种复杂因素的影响,导致很难准确地对森林火灾的蔓延与灭火过程进行仿真。对森林火灾的蔓延和细水雾灭火过程进行物理建模,蔓延模型采用树形模块结构来模拟树木燃烧的热解反应,并考虑了温度、风场、质量损失率等因素对树木燃烧蔓延的影响。在使用细水雾进行灭火仿真实验时,重点关注细水雾穿透火焰区域形成水膜以及水分蒸发导致的灭火作用,从而阻止森林火灾的蔓延,成功实现了交互灭火的仿真平台,可以让用户沉浸式地体验森林火灾的蔓延过程,并通过水枪、消防车和无人机进行细水雾灭火仿真实验。该研究成果对消防仿真领域方面的应用具有重要意义。

基于Sentinel-2的青铜峡灌区水稻和玉米种植分布早期识别

及时准确地掌握灌区内作物种植分布对于灌溉水资源高效配置、农田精准管理具有重要指导意义。以宁夏青铜峡灌区为研究对象,利用多时相Sentinel-2卫星数据,通过水稻和玉米早期特征分析,提取关键的“水淹”信号和“植被”信号,构建时序归一化差异水体指数(MNDWI)和归一化植被指数(NDVI)特征值数据集,并通过样本分析关键特征阈值,构建水稻和玉米早期种植分布决策树模型,提取2022年宁夏青铜峡灌区水稻和玉米种植的空间分布。结果表明(:1)玉米和水稻苗期的后半段5月15—31日,水淹信号和植被信号是区分二者关键时期。(2)基于早期作物物候特征的方法,在5月16—31日获取的水稻和玉米图像制图精度高于90%,用户精度超过91%,总体精度超过90%,Kappa系数高于0.88,明显高于同时期随机森林方法的分类精度。(3)本研究提出的方法在早期水稻和玉米种植分布提取方面具有较强的适用性,并且能够在时空尺度上以较少的实地样本进行延展,同时在时间上也更有优势。因此,该方法为青铜峡灌区水稻和玉米种植分布早期调查提供了重要的方法支撑。

Research on the Protection of Vulnerable Groups in Water Pollution Conflicts Based on Binomial Tree Pricing Model

The interests of vulnerable groups can’t be guaranteed due to their weaker capacity and the limited interests demand channels during the water pollution conflicts. The interest protection for the vulnerable people in the water pollution conflicts has attracted attentions of the international scholars. The paper tries to construct the market mechanism which can make the vulnerable people to involve in the emission trading. The vulnerable people can buy American put option in the emission trading market. When the price of the emission runs below the contract price, the vulnerable people can get the benefit through executing the option. When the price of the emission runs above the contract price, the vulnerable people can give up the right. The binomial tree option pricing model can help the vulnerable people to make a decision through the analysis of the worth of the American put option.

新型灌溉技术在果树中应用的研究进展

果树是我国农业中重要的支柱产业,而我国水资源匮乏是影响果树生产的瓶颈问题。近年,研究学者根据果树的需水特性、生长发育规律、栽培环境条件等因素,研制多种新型节水灌溉技术,并得到较好的试验印证效果,该文将国内外有关新型灌溉技术在果树中的研究进行综合阐述,并对今后新型灌溉技术进行展望,以期将新型灌溉技术更好地服务于果树生产、提高果园管理水平提供借鉴。

有机化蒙脱土对XLPE/OMMT纳米复合电介质微观形态及水树枝老化特性的影响

文中采用熔融共混法分别制备了交联聚乙烯/有机化蒙脱土(XLPE/OMMT)纳米复合电介质,研究有机化蒙脱土种类对纳米复合电介质微观形态和水树枝老化特性的影响。对试样进行力学性能测试发现,OMMT质量分数为0.5%时,综合力学性能达到最佳;利用差示扫描量热法和扫描电子显微镜研究了试样的微观形态,经双十八烷基苄基季铵盐有机化改性并细化的有机化蒙脱土(OMMT3)起到明显的异相成核作用,使晶体更加完善,结晶度高达25.3%,晶体平均尺寸仅为16.67μm;采用水针电极法对各试样进行加速水树枝老化试验,剥离分散的OMMT3片层形成了更加曲折的迷宫路径,其对水分子的阻隔效应与XLPE交联网状结构对分子链运动束缚的共同作用,有效抑制了XLPE/OMMT3试样中水树枝的生长,引发概率下降至23.4%;傅里叶变换红外光谱对水树枝老化前后的化学结构进行了表征,纳米复合电介质水树区的羰基指数增加、羟基振动峰增强,表明水树枝老化是电化学降解的作用;在水树枝生长过程中,XLPE/OMMT3试样老化断链较少,表现出较优的耐热氧老化性能。

浅水受限区水下油气田开发方案

针对国内浅水油气资源开发环境影响及空间受限等问题,本文提出了国产浅水水下生产系统的总体设计方案。通过对浅水水下生产系统关键设备结构进行分析,提出了一种满足受限区海域开发要求的环境友好型设计思路。结果表明:通过系统和总体布置的设计,国产浅水水下生产系统与深水相比在单体重量、作业方式、维护检修方面更加经济。

基于GBDT-LSTM的闽江流域水质预测

闽江作为福建省最大的河流,其生态保护对维护全省水生态环境而言意义重大。为进一步利用水质评价和预测方法对水质状况进行有效分析,选取闽江流域2017年1月-2023年8月共20处水质监测站数据作为研究对象,采用水质综合指数法对各站点水质状态进行判断;比较LSTM模型和GBDT-LSTM模型的拟合结果,并对各指标数据进行预测。结果表明,1)闽江流域各监测点除总氮外的水质指标均呈现较好趋势,各监测点的总氮浓度存在差异,整体情况较差,其中位于三明和南平市的河段由于当地重工业发达,导致水体中的硝态氮不断增加,进而致使河段内总氮浓度过高。2)流域水质的WQI值呈现逐年上升的趋势,水质状况普遍处于中等及以上水平,仅有少数监测点的水质状况处于很差状态,从中上游携带的泥沙等固体的堆积导致了连江琯头的水质情况较差;沙县斑竹溪渡口由于位于三明和南平的交界处,且沿岸分布较多重工业城市,故水质状态略差;相较于南平和三明的大型重工业企业,位于古田县的监测点以农业、轻工业为主,对水质指标的影响相对较小,水质状况因此较好。3)采用GBDT对变异程度较高的各水质指标在预测模型中的重要性进行排序,发现GBDT-LSTM混合模型的拟合效果相较于LSTM模型更好,更有利于对水质状况进行精确地预测。4)水体中总氮、高锰酸盐指数等含量的不断增加主要源于大量的工业废水,建议加强对临近闽江流域高污染高排放企业的控制,科学合理地实现工业污染排放和污染物容量在时空上的合理分配。