铣削斜楔形区域形成及其对流场负压区的影响规律

【目的】研究在内喷淋冷却高速铣孔加工中,铣削斜楔形区域的形成对流场负压区的影响。【方法】对高速湿式铣削加工区域建立三维流场模型,应用计算流体力学软件Fluent,采用非结构化四面体网格单元,利用滑移网格技术对高速铣削过程进行三维瞬态计算。【结果】得到不同刃数、不同转速的立铣刀对同一孔径工件进行切削时流场的压力分布情况。三刃立铣刀斜楔形对流场负压影响最大,当立铣刀刃数增加时,此斜楔形区缩小,负压减小,转速为10 000～20 000 r/min时增长速度逐渐降低,20 000～35 000 r/min时增长速度逐渐增高。【结论】从流场角度分析,流场中最大负压值与转速呈正相关,转速的提高增加了抑制空化的难度;增加铣刀刃数,可减小流场斜楔形区面积,减小空化可能。     

Effects of rainfall intensity and topography on rill development and rill characteristics on loessial hillslopes in China

Rill development is a major soil erosion process that causes severe soil degradation.This study examined the effects of representative rainfall intensities(50 and 75 mm h-1),slope gradients(10°and 150),and slope lengths(7.5 and 10.0 m)on rill development and rill characteristics on loessial hillslopes in China.Loessial soil was collected from the cropland of Ansai Town,Yan'an City,Shaanxi Province.The soil with 28.3%sand,58.1%silt,and13.6%clay was packed into a soil pan to conduct rainfall simulations in 2012.The results showed that the time of the knickpoint occurrence(5-16 min),the rill headcut extension(9-33 min),and the mean headward erosion rate(1.7-5.o cm min-1)were better representative indicators for reflecting the changes in the rill development than other indicators used in this study.For a quick evaluation of the rill erosion severity,the rill coverage ratio(1%-12%,generallyincreasing with an increase in the rainfall intensity)was better than the other indicators for treatments with different rainfall intensities,and the rill width-depth ratio(1.56-2.27,generally decreasing with an increase in the slope gradient)was better than the other indicators for treatments with different slope gradients.Furthermore,the rill inclination angle(8.2°-19.1°,significantly increasing with an increase in the slope length)and rill density(0.19-1.34 m·m-2,generally increasing with an increase in the slope length)were more suitable for evaluating the rill erosion severity on hillslopes with different slope lengths.Therefore,the representative indicators could reflect the differences in the rill development and rill characteristics under different rainfall and topographic situations.The study greatly improved the evaluation of rill erosion severity and the prediction of the development of rills for loessial hillslopes.     

顾及局部与结构特征的稀疏多项式逻辑回归高光谱图像分类方法

稀疏多项式逻辑回归在分类中仅利用图像光谱信息,导致分类效果不太理想.本文提出了一种顾及局部与结构特征的稀疏多项式逻辑回归高光谱图像分类方法.首先利用加权均值滤波与拓展形态学多属性剖面对原始高光谱图像进行局部与结构特征提取;然后对二者进行加权平均特征级融合以获取更具唯一性的像元特征;最后由稀疏多项式逻辑回归分类器对融合结果进行分类.结果表明,本文方法能有效地提高分类精度,而且具有较强的稳健性.     

GF-2支持下的干旱区稀疏植被区植被覆盖度估算

现有像元二分模型MODIS植被覆盖度模型因其形式简单、适用性较强的特点被广泛应用于区域植被覆盖度（FVC）的估算。然而,研究表明在沙漠和低植被覆盖的西部干旱区,从250 m的影像上很难精准地获取NDVI_veg（全植被覆盖植被指数）和NDVI_soil（全裸土区植被指数）参数。利用常用的直方图累计法获取模型所需参数NDVI_veg和NDVI_soil,估算结果存在普遍高估现象。为此,本文首先引入同期获取的GF-2号卫星数据,从GF-2号影像上提取植被覆盖像元;然后,利用Pixel Aggregate方法重采样至250 m分辨率,获取250 m空间分辨率下纯植被和纯裸土像元;最后,将纯植被和纯裸土像元各自空间位置相对应的MODIS NDVI数据最大值作为模型所需NDVI_veg和NDVI_soil参数,实现研究区内植被覆盖度的估算。试验通过与线性回归法、多项式回归法和直方图累计像元二分模型法估算结果进行精度对比,结果表明：利用GF-2影像辅助的像元二分模型,精准地获取了低植被覆盖区NDVI_veg和NDVI_soil模型参数,提高了干旱区植被覆盖度的估算精度,并有效地抑制了受稀疏植被影响NDVI在干旱区普遍偏高问题导致的FVC高估的现象。     

大跨径斜拉桥主梁线形测控新方法研究及应用

大跨径斜拉桥结构刚度小、变形大,为保证主梁顺利合龙,施工过程必须快速精确定位主梁上各个节段的平面和竖向线形。区别于传统的极坐标主梁平面线形测控方法,本文提出采用全站仪自由设站法测控主梁平面线形;同时区别于传统的水准测量方法,提出采用全站仪间接高差传递的方法测控主梁竖向线形。介绍了两种新方法的测量原理,通过工程实例论证了新方法的可行性和实用性,且能够大幅度提高测控效率,可为其他大跨径桥梁主梁线形的测控提供一定的参考。     

河流静水滩区潜流带水交换空间分布模式研究（英文）

Hyporheic zone(HZ) influences hydraulic and biogeochemical processes in and alongside streams, therefore, investigating the controlling geographic factors is beneficial for understanding the hydrological processes in HZ. Slack water pool (SWP) is an essential micro-topographic structure that has an impact on surface water and groundwater interactions in the HZ during and after high flows. However, only a few studies investigate HZ surface water and groundwater exchange in the SWP. This study used the thermal method to estimate the HZ water exchange in the SWP in a segment of the Weihe River in China during the winter season. The findings show that on the flow-direction parallel to the stream, river recharge dominates the HZ water exchange, while on the opposing flow-direction bank groundwater discharge dominates the water exchange. The water exchange in the opposing flow-direction bank is about 1.6 times of that in the flow-direction bank. The HZ water exchange is not only controlled by flow velocity but also the location and shape of the SWP. Great water exchange amount corresponds to the shape with more deformation. The maximum water exchange within the SWP is close to the river bank where the edge is relatively high. This study provides some guidelines for water resources management during flooding events.     

Farmer-based Rice Cropping Systems in the Poyang Lake Region,China: Analysis of Characteristics and Policy Implications

This paper examines the spatial characteristics of farmer/household behaviors in regional rice cropping systems (RCS), and the results provide necessary information for developing strategies that will maintain regional food security. Through field study and statistical analysis based on 402 households questionnaires finished in 2014-2015 in the Poyang Lake Region (PLR) of China, we arrived at two main conclusions. First, single- and double cropping rice were found across the study area, but showed a general distribution trend, with double cropping rice in the southeast part (especially in Jinxian county) and single cropping rice in the northwest (particularly in De’an county). Second, the household decisions concerning RCS varied in different parts of the PLR, but double cropping was the dominant type, with about 63.57% of the respondent households in the PLR cultivating double cropping rice. However, the multiple-cropping index of paddy rice was only 1.55. About 3% of interviewed households had altered their RCS during this period. Based on these findings, the local governments should guide farmers’ paddy field cultivation behaviors by increasing the comparative efficiency of rice production, promoting appropriate scale operations and land conversion, as well as optimizing rice growing conditions to improve the multiple cropping index and enhance food provision. Finally, land-use efficiency and more sustainable use of land resources should be improved.     

氨氮急性攻毒对水产经济动物棘胸蛙(Paa spinosa)蝌蚪死亡率、排氨率、耗氧率及窒息点的影响

以体长(1.932±0.204)cm、体质量(1.386±0.055)g的棘胸蛙蝌蚪为实验动物,在水温(24±0.2)℃、DO(7.30±0.01)mg/L、pH 7.30±0.01条件下,采用静水停食法开展了氨氮对蝌蚪的急性攻毒实验,并以此为基础,测定了不同氨氮质量浓度胁迫下棘胸蛙蝌蚪的排氨率、耗氧率、氧氮比及窒息点。结果表明:(1)蝌蚪对氨氮急性攻毒具明显的运动避毒行为,濒死个体的背部皮肤和肝脏均具明显的色变症状;(2)氨氮对蝌蚪的急性致死率具明显的剂量—时间效应,24h、48h、72h、96h LC50依次为177.5、151.7、148.6和146.8mg/L,毒性时段蓄积程度系数呈持续下降趋势,24—48h、48—72h、72—96h的时段MAC值分别为84.04%、10.1%和5.86%;(3)蝌蚪夜均、昼均、日均及时段排氨率随氨氮质量浓度增加均呈阶梯式下降趋势,其中时段排氨率与对照组均无显著差异的为9.80mg/L实验组,夜均、昼均、日均及时段排氨率与对照组均无显著差异的仅为2.45mg/L实验组(P0.05);(4)氨氮对蝌蚪呼吸耗氧具低毒兴奋效应,其夜均、昼均和日均耗氧率随氨氮质量浓度增加均呈先升后降趋势,峰值氨氮质量浓度范围均为4.90—7.35mg/L(P0.05),与对照组均无显著差异的仅为14.70mg/L实验组(P0.05),窒息点含氧量随氨氮质量浓度增加呈先降后升趋势,谷底出现于4.90mg/L实验组(P0.05),与对照组无显著差异的仅为9.80mg/L实验组(P0.05);(5)实验期间,蝌蚪氧氮比(O:N)波动于18.87—25.34之间,昼均和日均氧氮比(O:N)随氨氮质量浓度增加均依次呈"上升—稳定—下降—再稳定"之趋势,两者的峰值氨氮质量浓度范围分别为4.90—14.70mg/L和4.90—9.80mg/L,夜均氧氮比(O:N)呈先升后降趋势,峰值出现于7.35mg/L实验组(P0.05)。     

一例异育银鲫(Carassius auratus gibelio)暴发性出血病病原分析

2016年6月,江苏某异育银鲫(Carassius auratus gibelio)养殖场暴发一种传染性急性出血病,造成养殖银鲫大量死亡。为分析此次疾病病因及流行规律,本研究从发病养殖场采集患出血病的异育银鲫,从细菌、病毒及寄生虫三个方面对病原进行了分析。采用病原菌分离、组织病理学观察、超薄切片电镜观察、病毒核酸分析、回感实验等对病原进行鉴定。结果显示从发病鲫鱼体内分离到病毒一株,未发现寄生虫及细菌感染。经测序及序列分析,该病毒为鲤疱疹病毒Ⅱ型(Cyprinid herpesvirus2,CyHV-2)病毒,组织病理学观察结果显示患病鱼的鳃和肾脏有明显病变,电镜下可观察到病鱼脾脏组织有带囊膜的球形病毒,囊膜直径约为170—200nm,病毒衣壳直径约为110—120nm,核心直径约为60nm,用组织匀浆感染鲫鱼囊胚细胞系(CGB)可稳定地观察到典型的细胞病变,用患病鱼组织匀浆液人工感染异育银鲫的死亡率高达100%,荧光定量PCR检测到该病毒可感染多器官,其中以脾脏中病毒含量最高,其次是脑,肝脏中最少。本研究可为CyHV-2的诊断防控及疫苗研制提供资料。     

基于F型mtDNA D-Loop的厚壳贻贝(Mytilus coruscus)群体遗传多样性研究

为研究东海区厚壳贻贝(Mytilus coruscus)遗传多样性,以厚壳贻贝F mtDNA D-loop为标记,对浙江省舟山嵊山岛、宁波渔山岛、温州南麂岛、福建省宁德湾和莆田南日岛五个海区的厚壳贻贝群体进行了遗传分析。结果表明,厚壳贻贝各群体的遗传多样性差异不明显,在5个群体中,宁德群体的遗传多样性相对最丰富;将5个群体作为一个整体时,呈现出较高的单倍型多样性和较低的核苷酸多样性。对厚壳贻贝5个群体间的遗传分化系数(Fst)和基因流(Nm)进行检测,结果显示群体间Fst值都很低,但Nm值都很高(Nm绝对值1),表明5个群体间存在丰富的基因交流。但宁德群体与浙江沿海的3个群体(嵊山、渔山、温州)的Fst值相对较高,且差异显著(P0.5),表明宁德群体与这3个群体间出现遗传分化。本研究旨在为海洋经济贝类资源的保护管理提供理论依据。