陕北无定河流域土壤侵蚀与植被覆盖和降雨关系研究

基于2000—2014年陕北无定河流域日降水、DEM、土壤类型、MODIS NDVI等数据,利用修正通用土壤流失方程(RUSLE)估算了流域土壤侵蚀情况,定量分析了植被覆盖和降雨在土壤侵蚀中的作用,结果表明:(1)无定河流域土壤侵蚀以微度侵蚀为主,平均占流域面积的88.35%,各土壤侵蚀等级面积比例随等级的升高而降低。2000—2014年微度侵蚀面积比例为下降趋势,轻度及以上等级面积比例均为上升趋势。(2)不考虑降雨因子影响时,无定河流域仍以微度侵蚀为主,且为增加趋势,而其他土壤侵蚀等级均为下降趋势。不考虑植被覆盖因子时,流域土壤侵蚀与模型计算结果的变化趋势基本一致。(3)植被覆盖对土壤侵蚀面积比例和变化速率的贡献率分别为13.67%和24.55%,而降雨作用达到86.33%和75.44%,表明降雨是流域土壤侵蚀的主要动力和控制因子,降雨变化主导着流域土壤侵蚀变化过程。     

The effect of fertilizer placement on nitrogen uptake and yield of wheat and maize in Chinese loess soils

Field trials were carried out to study the fate of¹⁵N-labelled urea applied to summer maize and winter wheat in loess soils in Shaanxi Province, north-west China. In the maize experiment, nitrogen was applied at rates of 0 or 210 kg N ha^–1, either as a surface application, mixed uniformly with the top 0.15 m of soil, or placed in holes 0.1 m deep adjacent to each plant and then covered with soil. In the wheat experiment, nitrogen was applied at rates of 0, 75 or 150 kg N ha^–1, either to the surface, or incorporated by mixing with the top 0.15 m, or placed in a band at 0.15 m depth. Measurements were made of crop N uptake, residual fertilizer N and soil mineral N. The total above-ground dry matter yield of maize varied between 7.6 and 11.9 t ha^–1. The crop recovery of fertilizer N following point placement was 25% of that applied, which was higher than that from the surface application (18%) or incorporation by mixing (18%). The total grain yield of wheat varied between 4.3 and 4.7 t ha^–1. In the surface applications, the recovery of fertilizer-derived nitrogen (25%) was considerably lower than that from the mixing treatments and banded placements (33 and 36%). The fertilizer N application rate had a significant effect on grain and total dry matter yield, as well as on total N uptake and grain N contents. The main mechanism for loss of N appeared to be by ammonia volatilization, rather than leaching. High mineral N concentrations remained in the soil at harvest, following both crops, demonstrating a potential for significant reductions in N application rates without associated loss in yield.     

Accelerating 2D orthogonal matching pursuit algorithm on GPU

Two-dimensional orthogonal matching pursuit (2D-OMP) algorithm is an extension of the one-dimensional OMP (1D-OMP), whose complexity and memory usage are lower than the 1D-OMP when they are applied to 2D sparse signal recovery. However, the major shortcoming of the 2D-OMP still resides in long computing time. To overcome this disadvantage, we develop a novel parallel design strategy of the 2D-OMP algorithm on a graphics processing unit (GPU) in this paper. We first analyze the complexity of the 2D-OMP and point out that the bottlenecks lie in matrix inverse and projection. After adopting the strategy of matrix inverse update whose performance is superior to traditional methods to reduce the complexity of original matrix inverse, projection becomes the most time-consuming module. Hence, a parallel matrix–matrix multiplication leveraging tiling algorithm strategy is launched to accelerate projection computation on GPU. Moreover, a fast matrix–vector multiplication, a parallel reduction algorithm, and some other parallel skills are also exploited to boost the performance of the 2D-OMP further on GPU. In the case of the sensing matrix of size 128 \(\times \) 256 (176 \(\times \) 256, resp.) for a 256 \(\times \) 256 scale image, experimental results show that the parallel 2D-OMP achieves 17 \(\times \) to 41 \(\times \) (24 \(\times \) to 62 \(\times \) , resp.) speedup over the original C code compiled with the O \(_2\) optimization option. Higher speedup would be further obtained with larger-size image recovery.     

安全关键系统的栈空间分析研究

由于存储空间异常引起的系统故障,系统开发或维护人员很难从失效特征直接判断到根原因。另外,存储空间异常通常会引起整个系统崩溃,对于安全关键系统,如航空电子系统,系统的失效往往会引起坠机或人员伤亡,因此,对安全关键系统的空间分析显得尤为重要。由于系统栈空间的分析涉及系统动态运行状态,在程序的任意点都有可能被中断服务程序或实时操作系统的其它任务中断。此外系统的栈分析需要基于目标码等特性,再次增加了对于系统栈空间分析的难度。本文从栈空间分析的必要性出发,提出一种综合中断抢占图的栈分析理论和方法,并就安全关键系统如何保证栈空间使用的确定性进行论述。最后,就安全关键软件系统FCOS的栈空间分析过程进行详细的阐述。     

Improved conditional random fields model with multi-trigger embedding for Chinese event extraction

Event extraction is a challenging task in natural language understanding, which aims to recognize event type, subtype and roles of relevant entities from unstructured text. Most current approaches address event extraction with highly local models that extract event type and arguments independently. However, this multi-step method cannot make full use of the reciprocal dependency relationship between event trigger and arguments, especially for nested event structure. E.g. the trigger of a Life/Injure event is embedded inside the argument, and a trigger is an event anchor as well as a modifier of argument. Meanwhile, In the same label space, the example proportion of triggers to arguments is scare, and there exists the issue of unbalanced data. Therefore, this kind of trigger is apt to be labeled as the event argument. In order to let event type recognition and event argument recognition guide each other, and resolve the problem of unbalanced data, we consider event extraction to be a sequence labeling problem and build a novel improved conditional random fields joint labeling model with multi-trigger embedding. Experimental results on ACE 2005 Chinese corpus show that this method improves the performance of event extraction.     

Dirichlet边界条件的声波散射问题的两种数值方法

利用单层位势理论将声波散射的外边值问题转化为第一类边界积分方程,采用迭代的Tikhonov正则化和改进的Tikhonov正则化方法求解,给出了二维空间的数值实例。与Nystrom方法相比,计算简单得到的精度却一样。     

响应曲面法优化甘薯饮料配方的研究

以甘薯为实验材料,以甘薯浓缩汁、蔗糖、柠檬酸和甘薯香精为实验因素,利用响应曲面法进行实验设计,对甘薯饮料的最佳配方进行了研究,并对最佳配方进行了感官评价验证、理化指标检测和微生物学检测.通过对实验得到的回归方程和响应曲面分析得出甘薯饮料的最佳组合为100 mL饮料中甘薯浓缩汁1.28 mL,柠檬酸0.1 g,蔗糖5.41 g,甘薯香精2.84mL,感官评分为83.43.     

基于水量平衡的膜孔畦灌水流推进过程研究

通过引入地表储水形状系数和试验分析膜孔灌土壤入渗参数,基于水量平衡原理研究膜孔畦灌水流推进过程中入畦水量是由地表储水量、膜孔入渗水量和损失水量组成.结合田间水流推进试验,量化计算膜孔畦灌水流推进过程中损失水量与入畦流量的比值及灌溉水的有效利用率,并分析得出损失水量是由膜上积水和沿膜孔湿润体周围二维入渗的水量组成,沿膜孔湿润体二维入渗的水量提高了灌溉水的有效利用率,从而实现了水资源的高效利用,为推进膜孔灌的大田推广和发展提供技术依据,对发展节水农业和构建节水社会有一定的创新性.     

焦作市绿地格局与其紧急避难功能分析

城市绿地系统在改善生态环境,丰富城市景观等方面起着重要作用;同时,城市绿地本身还具有强大的防灾与减灾功能.以焦作市为例,结合市区绿地组成与格局,运用GIS软件工具对其绿地紧急避难有效空间,灾后3,5,7 min的紧急避难缓冲区覆盖面积、覆盖人口以及人均绿地安全区占有量进行分析.结果表明:焦作市建成区公园绿地、生产绿地、防护绿地较多,而附属绿地与其它绿地偏少;市民紧急避难人均占有量大于规定要求,但其在空间分布上极不均匀,特别是老城区部分地段尚不能满足紧急避难的需求;大块绿地过于集中,其辐射区域有限,有大面积的应急避难服务盲区存在.     

多通道Haar-like特征多示例学习目标跟踪

目的 提出一种基于多通道Haar-like特征的多示例学习目标跟踪算法,克服了多示例跟踪算法在处理彩色视频时利用信息少和弱特征不能更换的缺点。方法 首先,针对原始多示例学习跟踪算法对彩色视频帧采用单通道信息或将其简单转化为灰度图像进行跟踪会丢失部分特征信息的缺点,提出在RGB三通道上生成位置、大小和通道完全随机的Haar-like特征来更好地表示目标。其次,针对多示例学习跟踪算法中Haar-like弱特征不能更换,难以反映目标自身和外界条件变化的特点,提出在弱分类器选择过程中,用随机生成的新Haar-like特征实时替换部分判别力最弱的Haar-like特征,从而在目标模型中引入新的信息,以适应目标外观的动态变化。结果 对8个具有挑战性的彩色视频序列的实验结果表明,与原始多示例学习跟踪算法、加权多示例学习跟踪算法、基于分布场的跟踪算法相比,提出的方法不仅获得了最小的平均中心误差,而且平均跟踪准确率比上述3种算法分别高52.85%,34.75%和5.71%,在4种算法中获得最优性能。结论 通过将Haar-like特征从RGB三通道随机生成,并将判别力最弱的部分Haar-like弱特征实时更换,显著提升了原始多示例学习跟踪算法对彩色视频的跟踪效果,扩展了其应用前景。