三峡工程动工三年来两坝间河道演变分析

根据葛洲坝运行以来的实测资料，首先分析了两坝之间达到冲淤平衡后河道的基本状况，然后重点分析了三峡工程动工以后两坝间河道的演变情况。认为三峡工程动工后，对两坝间 影响主要在：（１）施工中的填方和弃渣增大了河道的淤积量，增大了葛洲坝的库容损失；（２）弃渣使泥沙组成粗化，这有可能增大葛洲坝水轮机的磨损；（３）对航道的影响在三峡坝区主要是航道变窄，但航深仍能保持施工前的水平。     

共轭梯度法优化设计低噪声FET放大器

本文利用放大器的噪声系数及增益表达式,构成目标函数,再利用共轭梯度和三次插值法进行计算机优化。用编制的优化程序AMAD设计、制作了一个S波段低噪声放大器,达到了较为满意的指标,较好地满足了系统组件的要求。     

新疆地州经济发展的梯度化差异研究

新疆地域广袤,区域经济发展差异较大,区域经济的差异已影响到新疆经济社会的可持续发展.研究新疆地州经济的区域差异,并根据差异现状进行分组,有利于新疆根据地州经济的梯度类型制定相应的倾斜政策,争取相应的对口支援,以促进新疆经济社会的均衡发展.本文借助方差分析的方法,结合逐步回归的思想,按经济发展水平和经济增长状况将新疆各地州经济差异水平客观地划分为五个梯度.划分结果显示：27％的地区属于经济发展水平较高的地区,33％的地区属于经济增长较快的地区,53％的地区属既属于经济发展水平较低区域,又属于经济增长较慢的地区,也即新疆各地州经济发展水平整体偏低,发展的均衡性较差;从发展态势来看,新疆各地州梯度差异将进一步扩大,动态上虽然会有所调整,但调整的结果不会显著.     

Macroinvertebrate responses along a complex regulated stream environmental gradient

Samples were collected year-round over a one-year period at sites located downstream from a hypolimnetic-release reservoir on the Blue River, Colorado, to examine macroinvertebrate responses along a complex environmental gradient induced by river regulation. Six sampling sites were established in riffles downstream of the dam using approximately a geometric progression starting at 0.25 km. Ordination techniques were used to elucidate macroinvertebrate distributional patterns along the complex environmental gradient. The detrended correspondence analysis (DCA) showed a sequential faunal gradient with the most rapid change occurring within the first 2.0 km below the impoundment. Detrended canonical correspondence analysis (DCCA) was used to relate faunal distributions to downstream changes in environmental variables. Downstream decreases in periphyton standing crop and minimum temperatures, and downstream increases in food resources and maximum temperatures, were identified as the major variables structuring faunal assemblages. The combined use of different gradient analysis techniques proved useful for identifying distinct macroinvertebrate distributional patterns and the environmental variables that may be responsible for these patterns.     

Blending gradient boosted trees and neural networks for point and probabilistic forecasting of hierarchical time series

In this study, we addressed the problem of point and probabilistic forecasting by describing a blending methodology for machine learning models from the gradient boosted trees and neural networks families. These principles were successfully applied in the recent M5 Competition in both the Accuracy and Uncertainty tracks. The key points of our methodology are: (a) transforming the task into regression on sales for a single day; (b) information-rich feature engineering; (c) creating a diverse set of state-of-the-art machine learning models; and (d) carefully constructing validation sets for model tuning. We show that the diversity of the machine learning models and careful selection of validation examples are most important for the effectiveness of our approach. Forecasting data have an inherent hierarchical structure (12 levels) but none of our proposed solutions exploited the hierarchical scheme. Using the proposed methodology, we ranked within the gold medal range in the Accuracy track and within the prizes in the Uncertainty track. Inference code with pre-trained models are available on GitHub.¹     

渝昆高速铁路会泽至蒲草塘段线路走向及坡度方案研究

渝昆高速铁路会泽至蒲草塘段地质条件复杂,自然保护区遍布,是渝昆高速铁路的建设难点。在阐述渝昆高速铁路会泽至蒲草塘段线路概况的基础上,从工程地质、环境敏感区影响、工程投资、工程实施难易程度及工程可实施性5个方面对线路走向进行研究,确定待补东绕方案为最佳线路走向方案。从调整线路平面和纵断面2个方面进行坡度软化方案比选,对坡末速度进行分析,合理确定渝昆高速铁路会泽至蒲草塘段线路走向及坡度方案,为渝昆高速铁路全线早日接入我国高速铁路网络奠定基础。     

葛洲坝大江下航道水流条件分析

航道水流条件是保证船舶航行安全的主要问题之一。葛洲坝大江下游引航道由于受枢纽泄洪影响，航道内存在明显的泄水波和高流速区，造成船舶航行困难，影响安全。因此，现行船舶只在流量２００００ｍ＾３／ｓ以下通行。为此，近年来，对原型水流条件作了大量观测，探讨提高通航流量的可能性。经分析认为，在现行条件下，通航流量可提高到２３０００ｍ＾３／ｓ。     

人熊赛跑:中国高铁站点争夺的区域竞争新解释

作为构建综合交通运输体系和现代化经济体系的基石,中国高速铁路极大地改变了国民生产生活方式、影响了资源空间配置效率并重塑了经济地理。中国高速铁路的飞速发展,一方面导致生产要素和资源的空间集聚和中小城市的外围化,另一方面却出现了愈演愈烈的中小城市高铁站点争夺运动。中小城市通过高铁站点争夺以“竞劣”?为了回答这一“悖论”,文章基于夜间灯光数据和密度梯度指标,对以省会城市或中心城市为核心的空间集聚程度进行了重新测度;在此基础上,提出了开通高铁的中心城市和争夺高铁的中小城市之间的“人熊赛跑”理论假说,并利用数据对这一假说进行了验证。文章研究发现：（1）高铁的开通,导致经济活动向省会城市或中心城市的集聚,而中小城市被边缘化,即“人跑不过熊”;（2）开通高铁的中小城市相对于未开通高铁的中小城市而言,其能获得相对较快的经济增长,即“跑过了同伙”;（3）“人熊赛跑”的理论逻辑,很好地解释了中小城市通过高铁站点争夺以“竞劣”这一“悖论”,即“跑不过熊,但要跑过同伴”。文章的研究,为中国高铁站点争夺的空间政治经济学问题,提供了一个合理的理论解释。     

Forecasting with trees

The prevalence of approaches based on gradient boosted trees among the top contestants in the M5 competition is potentially the most eye-catching result. Tree-based methods out-shone other solutions, in particular deep learning-based solutions. The winners in both tracks of the M5 competition heavily relied on them. This prevalence is even more remarkable given the dominance of other methods in the literature and the M4 competition. This article tries to explain why tree-based methods were so widely used in the M5 competition. We see possibilities for future improvements of tree-based models and then distill some learnings for other approaches, including but not limited to neural networks.     

A streamline approach for identification of the flowing and stagnant zones for five-spot well patterns in low permeability reservoirs

The mechanism of the fluid flow in low permeability reservoirs is different from that in middle-high permeability rese-rvoirs because of the existence of the Threshold Pressure Gradient (TPG). When the...