Empirical predictors of annual bed load travel distance,and implications for salmonid habitat restoration and protection

Measurements of annual travel distance (L_b) of bed load sediment at 16 locations in Alaska, the intermountain USA, west coast USA and Scotland are strongly correlated with bankfull channel width (r² = 0·86, p < 0·001). Travel distance of particles is probably limited by trapping in bars, which have a longitudinal spacing proportional to channel width. Increased abundance of woody debris reduces bar spacing and may reduce L_b. Longer cumulative duration of bed load transporting flows in a year appears to increase L_b. Other predictors of annual travel distance such as stream power per unit length, drainage area and bankfull discharge were less well correlated with L_b (r² ranging from 0·27 to 0·51). Stream power per unit bed area, basal shear stress and slope were not significantly related to L_b (r² < 0·05). Most correlations were improved when regressions were limited to data from the west coast USA. Travel distance estimates can be used to help identify reaches that may take longer to recover from large, short‐term increases in sediment supply. Published in 2001 by John Wiley & Sons, Ltd.     

地震层析成像技术在岩体完整性测试中的应用

地震波层析成像借鉴了医学上X射线断面扫描的基本原理,利用地震波穿过地质体后走时及能量的改变等物理信息,通过数学处理重建地质体内部图像,从而得到所研究地质体的岩性及构造分布。本文利用这种方法,在一个钻孔中利用电火花震源激了弹性波,在另一个钻孔布设多个检波点同时接收,拾取弹性波初至时间,将接收到的数据利用SIRT方法进行反演迭代计算,最终形成一个弹性波速度谱图,然后利用岩土体的弹性波速度差异推断岩体完整性分布。与其它测试方法比较,该方法分辨率高,空间位置准确,在工程物探、岩土工程勘察中具有较好的应用前景。     

Errors due to the anisotropic-common-ray approximation of the coupling ray theory

The common-ray approximation eliminates problems with ray tracing through S-wave singularities and also considerably simplifies the numerical algorithm of the coupling ray theory for S waves, but may introduce errors in travel times due to the perturbation from the common reference ray. These travel-time errors can deteriorate the coupling-ray-theory solution at high frequencies. It is thus of principal importance for numerical applications to estimate the errors due to the common-ray approximation applied. The anisotropic-common-ray approximation of the coupling ray theory is more accurate than the isotropic-common-ray approximation. We derive the equations for estimating the travel-time errors due to the anisotropic-common-ray (and also isotropic-common-ray) approximation of the coupling ray theory. The errors of the common-ray approximations are calculated along the anisotropic common rays in smooth velocity models without interfaces. The derivation is based on the general equations for the second-order perturbations of travel time.     

Study on fine structure of crust-mantle transition zone in Yanqing-Hailai basin based on CDP and DSS data

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INTERSTATE HIGHWAY EXIT MORPHOLOGY: NON-METROPOLITAN EXIT COMMERCE ON 1-75*

The commercial non-metropolitan exit clusters of America's interstate highway system exhibit regularities of basic form, scale, mix of services provided, and the ordinal placement of establishments relative to the exit proper. An examination of 354 exits serving 1-75 indicates the typical morphology of interstate exit clusters.     

交通大数据在人文与经济地理学的应用及学科影响

交通大数据能够反映人类社会经济活动产生的位移与时空轨迹,不仅能够满足学者们在微观尺度更深入、更精细的研究粒度要求,而且能够为宏观尺度的研究提供广范围、多视角的连续性观测,其研究与发展为人文与经济地理学带来了新思路和新技术。本文以交通大数据的研究前沿为基础,梳理了区位论、时空行为、复杂网络、流空间等理论研究的发展方向,勾勒了“大数据时代”背景下人文与经济地理学的研究框架体系,探讨了新旧技术方法融合的可能性,并讨论了对各个分支学科相关研究的影响。接着,本文总结了交通大数据在人文与经济地理学的主要应用方向与趋势,主要包括出行即服务的交通规划理论与方法,“人工智能+大数据”的城市管理科学,大尺度交通流迁移的模拟,以及“流空间”与“场所空间”的多维度研究等。最后,本文指出了交通大数据应用在获取难度和数据有偏性等方面值得注意的问题并进行了展望。     

Ronge-Kutta法在计算复杂构造区域地震波旅行时中的应用

采用Ronge-Kutta射线追踪法对地震勘探中几个典型地质模型的地震波射线路径和旅行时计算的实例和效果进行分析。将Ronge-Kutta射线追踪模拟的结果与程函方程计算的时距曲线结果进行对比,验证了Ronge-Kutta射线追踪法的易实现性和程函方程有限差分旅行时算法的强稳定性,表明Ronge-Kutta射线追踪法在复杂构造区域进行地震射线路径和旅行时计算时能得到较好的模拟效果。     

丽水市旅游气候舒适度分析

采用人体舒适度气象指数（BCMI）、寒冷指数（CI）、温湿指数（THI）和度假气候指数（HCI）等4个综合性的气候指标,对丽水市的旅游气候舒适度进行了分析评价,并着重对比分析了BCMI和HCI对旅游气候适宜性的表征能力。结果表明：丽水市全年有8个月BCMI处在4～6级之间,属一类气候适宜区;冬季CI值较低,无严寒现象,夏季低海拔地区THI值偏高,但海拔600 m以上地区（约占市域面积6成）THI值较低,适宜“避暑纳凉”;HCI比传统的BCMI表现的更客观、更全面,它不仅考虑了气候的热舒适性影响,还考虑了降水和云量对旅游出行及观光的影响,且就时间尺度而言,HCI更适合旅游舒适度逐日预报的开展。     

基于改进的双线性旅行时插值的三维射线追踪

旅行时射线追踪的精度和效率一直是影响地震层析成像质量和效果的关键因素。这里在三维近地表速度结构层析成像应用中,结合旅行时插值算法与最短路径算法,提出了一种三维初至波射线追踪算法。通过对双线性旅行时插值算法进行改进,并运用判定条件与简化插值计算公式进行快速计算,减少了插值次数,降低了运算量,同时也保证了较高的射线精度,有效地解决了三维射线追踪算法的计算低效率,射线精度不高的问题。     

基于移动式监测的道路PM2.5浓度精细化时空模拟

作为主要的大气污染指标,PM_2.5浓度常来源于固定环境监测站点的监测与遥感影像数据,但时空精度普遍不足,难以揭示微尺度下城市内部PM_2.5时空分布情况。本文利用移动式监测方法,选择典型工作日(2017年11月27日),对广州市主城区道路以1 s和1 m为时空粒度进行PM_2.5浓度数据采集,并以早、晚出行高峰时段为对象,通过机器学习方法模拟道路PM_2.5精细化时空分布格局。结果表明,主城区早高峰道路PM_2.5浓度值相近的平均范围为24 m,晚高峰为15 m,PM_2.5浓度存在微尺度的时空异质性。利用多层感知器(MLP)构建的早、晚高峰PM_2.5浓度模型,拟合度分别达到0.70和0.68,明显优于传统的普通最小二乘法(OLS)线性回归模型。模型揭示出早高峰主城区全路网PM_2.5平均浓度为30.19μg/m3,晚高峰达到44.55μg/m3,部分高达94.82μg/m3,且“西高东低”的分布特征显著。本文提出的PM