Finsler 流形的 Cartan 型1形式的一些性质

给出了 Cartan 型1形式的外微分与 Bott 陈联络的曲率之间的关系，探讨了其与畸变、 S 曲率之间的关系，证明了 Berwald 流形的 Cartan 型1形式为恰当形式。利用 Cartan 型1形式构造了 Finsler 流形的射影球丛上的一个 Randers 度量，证明该度量为 Landsberg 度量的充要条件是底流形为 Riemann 流形。证明了 Cartan 型1形式及Cartan 1形式的对偶向量场为共型向量场的充要条件是底流形为 Riemman 流形。     

The impact of road geometry and surface roughness on fuel consumption of logging trucks

Fuel accounts for more than 35% of transport costs in Swedish forestry, and reduced fuel consumption would provide immediate economic and environmental benefits. The objective of this study was to quantify the effect of road gradient, curvature and surface roughness on fuel consumption of a conventional 60-ton logging truck. The study used a 320-km test track on both public and forest roads. The track was driven with various load weights in both dry summer and wet autumn conditions. Fuel consumption data were retrieved from the truck's CAN-bus system, and road data were measured with a profilograph. Average fuel consumption was 71.4?litres/100?km. A regression analysis showed that the most important factor was the interaction between vehicle weight and gradient, explaining the 86% increase between empty and fully loaded truck. In addition, the regression analysis quantified the individual effects of undulation, curvature and surface roughness, explaining the 107% increase in fuel consumption between the highest and lowest road class. Results from the proposed regression model (R² of 84% for a road section length of 1000?m) were consistent with predictions given by the European ARTEMIS model, and the proposed model can be used to improve cost estimation and route selection.     

基于改进最大值法合成NDVI的夏玉米物候期遥感监测

利用遥感技术监测农作物物候期,能够及时有效地评估作物生长趋势、提高农情信息化管理水平。本研究利用2016年MODIS 8天合成数据,提出改进的最大值合成法,结合S-G滤波和Logistic函数拟合重构夏玉米生长曲线,最后利用曲率法提取夏玉米的拔节期和成熟期,利用动态阈值法提取夏玉米的出苗期和抽雄期。结果表明:采用本文提取的夏玉米物候期与实测物候期相比,平均误差为2.76 d,其中在抽雄期的绝对误差为1.06 d,运用改进的最大值合成提取作物NDVI时序数据可有效去除连续云雾对植被指数的影响,提高监测作物物候期的准确性,为精准农业提供技术支撑。     

反弧段体型对高流速泄洪洞水力特性的影响

利用流体仿真软件FLUENT对高水头明流泄洪洞不同体型反弧段的水流流场进行三维数值模拟,获取了流速、压强、切应力等水流运动参数的沿程分布。结果表明:不同形式的反弧段,沿程水头损失差别很小;反弧段的曲率半径越小,底板压强越大,同时在反弧段始、末断面附近的压强梯度也大;各种类型的反弧段底板剪应力基本呈沿程增大的趋势,但前半部和后半部底板切应力的变化规律不同。综合考虑反弧段流速、底板压强、底板切应力的沿程分布情况,采用下过渡曲线形式的反弧段体型可以减小反弧段与下斜坡段连接部位的压强梯度和切应力,相对于文中提到的其他体型的反弧段,空蚀风险最小。     

Keratometry in normal cats: a cross-sectional study in Japan using an automated handheld keratometer

Keratometry was performed in 73 domestic cats of varied signalment in Japan using an automated handheld keratometer. The mean corneal curvature radius was significantly lower for cats younger than 1 year than for those older than 2 years (8.04 mm vs. 8.80−8.99 mm, P<0.01). The radius was significantly greater in males than in females among the cats older than 11 years (9.22 mm vs. 8.84 mm, P=0.01), while the age distributions of the males and females were similar. Corneal astigmatism did not significantly differ across the gender and age groups. The predictability of the corneal curvature and astigmatism was approximately 41−43% and less than 3%, respectively, as a function of age and bodyweight. The results highlighted some age- and sex-related keratometric variations in domestic cats in Japan.     

点云数据抽稀与加密对微地形数据分析的影响

针对不同观测尺度下,大起伏(20cm耕作处理)、微起伏(耙平裸坡处理)两种地形的点云数据进行抽稀、加密处理,选取地表曲率、坡向、地表糙度3种直观的指标对抽稀、加密处理对微地形数据分析的影响进行了评价。结果显示:抽稀与加密处理对于起伏较大的地形曲率影响更为明显,对于起伏较小的地形则影响不显著。5,10mm数据抽稀与加密处理后坡向变化不显著。1mm尺度抽稀地表糙度的影响十分规律,5mm加密与抽稀对于大起伏地形的影响十分复杂,10mm加密对于大起伏地形糙度变化较为复杂,裸坡变化则相对规律。     

虚拟犁体曲面的性能分析

以LEMLON犁体曲面为基础,在Pro/E中分析了犁体曲面的基本性能,指出其存在的问题;然后,在An-sys上对梨体曲面进行有限元分析,找出了犁体曲面在设计中的薄弱环节,从而为犁体曲面的优化设计提供了有利的支撑。     

秸秆添加与土壤基质势对棕壤压缩回弹特性的影响

土壤板结是农田土壤退化问题之一,秸秆还田是提高土壤有机质含量、改良土壤的重要措施。但秸秆还田和土壤基质势对土壤板结的影响尚不明确。试验设0,3,5 g/kg 3个秸秆添加量处理,以及高(1 000 kPa)、中(100 kPa)、和低(10 kPa)3个土壤基质势处理。通过固结试验,测定不同处理的压缩曲线并计算压缩回弹特性指标。结果表明:秸秆添加量、土壤基质势及其二者间的交互作用对压缩曲线最大曲率、预固结压力值、压缩指数和回弹指数的影响都达到显著性水平。预固结压力值、压缩指数和回弹指数均随着秸秆添加量的增加而增大,而最大曲率则随着秸秆增加量的提高而降低。土壤基质势与压缩曲线最大曲率、预固结压力值和压缩指数均呈正相关关系。回弹指数随着土壤基质势的增加呈现先降低后增加的趋势。秸秆添加有助于提高土壤回弹和抗压缩特性。     

计算机辅助流体曲面优化设计的探讨

从流体曲面设计的优化目标出发，导出了应用于流体曲面设计的一般流体光顺性条件一，同时对理论流场进行了射影综合分析，为选择现有数学样条函数或曲面进行流体曲面设计了提供了依据。