Effects of changes in canopy interception on stream runoff response and recovery following clear-cutting of a Japanese coniferous forest in Fukuroyamasawa Experimental Watershed in Japan     

Tomoki Oda  Tomohiro Egusa  Nobuhito Ohte  Norifumi Hotta  Nobuaki Tanaka  Mark B. Green  Masakazu Suzuki 《水文研究》2021,35(5):e14177

Understanding changes in evapotranspiration during forest regrowth is essential to predict changes of stream runoff and recovery after forest cutting. Canopy interception (Ic) is an important component of evapotranspiration, however Ic changes and the impact on stream runoff during regrowth after cutting remains unclear due to limited observations. The objective of this study was to examine the effects of Ic changes on long-term stream runoff in a regrowth Japanese cedar and Japanese cypress forest following clear-cutting. This study was conducted in two 1-ha paired headwater catchments at Fukuroyamasawa Experimental Watershed in Japan. The catchments were 100% covered by Japanese coniferous plantation forest, one of which was 100% clear-cut in 1999 when the forest was 70 years old. In the treated catchment, annual runoff increased by 301 mm/year (14% of precipitation) the year following clear-cutting, and remained 185 mm/year (7.9% of precipitation) higher in the young regrowth forest for 12–14 years compared to the estimated runoff assuming no clear-cutting. The Ic change was −358 mm/year (17% of precipitation) after cutting and was −168 mm/year (6.7% of precipitation) in the 12–14 years old regrowth forest compared to the observed Ic during the pre-cutting period. Stream runoff increased in all seasons, and the Ic change was the main fraction of evapotranspiration change in all seasons throughout the observation period. These results suggest that the change in Ic accounted for most of the runoff response following forest cutting and the subsequent runoff recovery in this coniferous forest.  相似文献   

埋深对恐龙化石的影响效果研究          下载免费PDF全文

陈诚  贾超  张尚坤  杜圣贤  罗文强  田京祥 《山东国土资源》2019,35(5)

已发现的恐龙化石大多数埋藏在不同深度的地层中,不同埋深化石所受风化破坏程度不尽相同。为深入研究恐龙化石的风化机理,探究恐龙化石的保护措施和方法,重点分析埋深产生的侧向压力对恐龙化石强度和破坏特性的影响。通过有限差分软件FLAC3D进行数值模拟,揭示埋深因素对恐龙化石保存的影响程度。试验结果表明:围岩对恐龙化石施加的侧向压力是影响恐龙化石变形和强度特性的一个重要因素。在弹性变形阶段,恐龙化石的初始强度、峰值强度随侧向压力的增大而不断增大。当应力超过了恐龙化石极限强度后进入塑性变形,其初始强度、峰值强度逐渐减小,最终达到残余强度。  相似文献   

Validation of the SCEC Broadband Platform simulations for tall building risk assessments considering spectral shape and duration of the ground motion     

Nenad Bijelić  Ting Lin  Greg G. Deierlein 《地震工程与结构动力学》2018,47(11):2233-2251

Earthquake simulation technologies are advancing to the stage of enabling realistic simulations of past earthquakes as well as characterizations of more extreme events, thus holding promise of yielding novel insights and data for earthquake engineering. With the goal of developing confidence in the engineering applications of simulated ground motions, this paper focuses on validation of simulations for response history analysis through comparative assessments of building performance obtained using sets of recorded and simulated motions. Simulated ground motions of past earthquakes, obtained through a larger validation study of the Southern California Earthquake Center Broadband Platform, are used for the case study. Two tall buildings, a 20‐story concrete frame and a 42‐story concrete core wall building, are analyzed under comparable sets of simulated and recorded motions at increasing levels of ground motion intensity, up to structural collapse, to check for statistically significant differences between the responses to simulated and recorded motions. Spectral shape and significant duration are explicitly considered when selecting ground motions. Considered demands include story drift ratios, floor accelerations, and collapse response. These comparisons not only yield similar results in most cases but also reveal instances where certain simulated ground motions can result in biased responses. The source of bias is traced to differences in correlations of spectral values in some of the stochastic ground motion simulations. When the differences in correlations are removed, simulated and recorded motions yield comparable results. This study highlights the utility of physics‐based simulations, and particularly the Southern California Earthquake Center Broadband Platform as a useful tool for engineering applications.  相似文献   

填充墙刚度影响的实测高层建筑增量动力分析          下载免费PDF全文

周云  裴熠麟  周祎  方亮  易伟建 《地震工程学报》2018,40(5):883-890

高层结构中的填充墙在地震作用下与周围结构构件之间的相互作用十分复杂,对建筑结构的整体抗震性能具有较大影响。然而我国规范在设计阶段通常不考虑填充墙对结构抗震性能的影响,统一采用周期折减系数来考虑其刚度变化引起的内力变化,因此准确评估填充墙对结构抗震性能的影响具有重要意义。本文在对一栋框-剪结构和一栋剪力墙高层建筑进行随机振动测试的基础上,利用Perform-3D对每栋高层分别建立了3种分析模型。其中对未考虑填充墙作用的结构模型,分别采取规范建议值和实测结果值两种方式进行周期折减。对通过添加斜撑单元来考虑填充墙作用的结构模型,利用环境激励测试识别获得的结构模态信息进行模型修正。对该3种模型进行了增量动力分析,探讨潜在危险性水平地震作用下填充墙对高层建筑抗震性能的影响。结果表明,填充墙增加了结构在弹性阶段的整体初始刚度,但随着地震动强度的增加逐渐丧失对结构刚度的贡献作用。相比考虑了填充墙作用的模型计算结果,规范建议的周期折减系数较为保守。同时研究发现,填充墙对高层框-剪结构的影响程度要比剪力墙结构大。  相似文献   

Wintertime rates of net primary production and nitrate and ammonium uptake in the southern Benguela upwelling system     

RF Flynn  JM Burger  K Pillay 《African Journal of Marine Science》2018,40(3):253-266

The elevated levels of primary productivity associated with eastern boundary currents are driven by nutrient- rich waters upwelled from depth, such that these regions are typically characterised by high rates of nitrate-fuelled phytoplankton growth. Production studies from the southern Benguela upwelling system (SBUS) tend to be biased towards the summer upwelling season, yet winter data are required to compute annual budgets and understand seasonal variability. Net primary production (NPP) and nitrate and ammonium uptake were measured concurrently at six stations in the SBUS in early winter. While euphotic zone NPP was highest at the stations nearest to the coast and declined with distance from the shore, a greater proportion was potentially exportable from open-ocean surface waters, as indicated by the higher specific nitrate uptake rates and f-ratios (ratio of nitrate uptake to total nitrogen consumption) at the stations located off the continental shelf. Near the coast, phytoplankton growth was predominantly supported by ammonium despite the high ambient nitrate concentrations. Along with ammonium concentrations as high as 3.6 µmol l^–1, this strongly suggests that nitrate uptake in the inshore SBUS, and by extension carbon drawdown, is inhibited by ammonium, at least in winter, although this has also been hypothesised for the summer.  相似文献   

阿拉尔河悬浮物对铀的吸附影响研究          下载免费PDF全文

钟翼  许建新  韩积斌  徐凯 《盐湖研究》2020,28(1):112-122

为了解阿拉尔河悬浮物对铀的吸附特性,通过静态吸附实验,研究了吸附时间、pH值、温度和铀初始浓度等因素对模拟含铀水中U(VI)去除率的影响,并从热力学和动力学方面对吸附过程进行了分析。结果表明,在T=25℃,溶液初始pH=7,接触时间为16 h时,悬浮物对铀的平衡吸附率最佳,为95.48%。随着铀初始浓度的增加,吸附量增加,但吸附率随之下降,升高温度有利于铀的吸附。铀在悬浮物上的吸附过程符合Langmuir等温吸附方程,说明悬浮物对铀为单分子层吸附,且化学吸附占主导地位。吸附动力学过程可用准二级吸附动力学模型描述,表明吸附主要受动力学控制,由两个以上步骤共同控制。FTIR和EDS分析结果表明,吸附过程中铀主要与悬浮物表面活性基团螯合并以表面络合吸附为主。吸附前后的能谱对比分析表明,吸附过程中存在离子交换行为。因此,悬浮物对铀的吸附机理是以表面络合吸附和离子交换为主、物理吸附为辅的混合吸附过程。  相似文献   

能力培养为导向的实践课程改革与设计     

刘亚文  王玥  段延松 《测绘通报》2020,(4):152-156

大学实践课程是培养学生创新、创业实践能力的重要环节，本文在新工科实验课程建设中，提出了以能力培养为导向的实践课程设计思路，旨在培养适应当今新技术、新产业、新模式快速变革时代的创新性工程科技人才。本文将传统的验证性实践课程调整为“目标设定、方案规划及实施”的设计型实验课程，强调学生在实践中的主体地位，遵循实践能力培养的规律，引导学生在实践中重参与、重思考、重实施、重过程。同时，将行业的最新发展、最新变革反映在实践教学课程中，增加了新型传感器及混合云人机协作数据处理平台，确保学生获取的知识和技术与快速发展的行业水平相接轨。本文以摄影测量实习课程改革为例，实践证明，课程的实施对于培养学生综合分析设计、创造性解决专业问题的能力取得了较好的效果。  相似文献   

A New Retracking Technique for Brown Peaky Altimetric Waveforms     

Fukai Peng 《Marine Geodesy》2018,41(2):99-125

A new Brown-Peaky (BP) retracker has been developed for peaky waveforms that usually appear within ～10 km to the coastline. The main feature of the BP is that it fits peaky waveforms using the Brown model without introducing a peak function. The retracking strategy first detects the peak location and width of a waveform using an adaptive peak detection method, and then estimates retracking parameters using a weighted least squares (WLS) estimator. The WLS assigns a downsized weight to corrupted waveform gates, but an equal weight to other normal waveform gates. The BP retracker has been applied to 4-year Jason-1 waveform (2002–2006) in two Australian coastal zones. The results retracked by BP, MLE4 and ALES retrackers have been validated against tide-gauge observations located at Burnie, Lorne and Broome. The comparison results show that three retrackers have similar performance over open oceans with the correlation coefficient (～0.7) and RMSE (～13 cm) between altimetric and tide-gauge sea levels for distance >7 km offshore. The main improvement of BP retracker occurs for distance ≤7 km to the coastline, where validation results indicate that data retracked by BP are more accurate (15–21 cm) than those by ALES (16–24 cm) and MLE4 (19–37 cm).  相似文献   

Non-symmetrical levee breaching processes in a channel bend due to overtopping     

Songbai Wu  Minghui Yu  Hongyan Wei  Yanjie Liang  Jing Zeng 《国际泥沙研究》2018,33(2):208-215

A series of experiments were done to reveal the overtopping breaching process of non-cohesive and cohesive levees in a U-bend flume. The flood hydrograph and breaching geometry were measured and analyzed in detail. The results show that the levee breaching processes can be briefly divided into four stages: slope erosion, longitudinal headward gully-cutting, lateral erosion, and relative stabilization. For non-cohesive levees, non-symmetrical lateral development of the breach occurs throughout the four stages, and the final non-symmetrical coefficient is approximately 2.2–2.6. Larger flow discharge or higher water level can accelerate the breaching process, while coarser sands tend to accelerate the process initially but depress the process at the end. The fluvial erosion rate of a non-cohesive breach shows a power-function relation with the excess wall shear stress. For cohesive levees, a plateau forms in the breach partially blocking the flow in the first two stages. The breach flow is approximately perpendicular to the levee body, and, thus, the erosion rates of the two breach sides are almost the same. Non-symmetrical lateral development mainly occurs in the third stage when the deep gully forms. The final non-symmetrical coefficient is approximately 2.7–3.3. It is expected that these findings can provide a valuable experimental dataset and a theoretical basis for breach closure and flood alleviation.  相似文献   

断层氢气观测技术实验     

谢恒义  李源  夏修军  孙召华 《地震地磁观测与研究》2018,39(4):176-182

采用ATG-6118H痕量氢在线自动分析仪，在朱夏-商丹断裂带南阳地区布设独山、马山口2个氢气观测台，研究设备取气深度、抽气时间设置长短对观测断层氢气浓度的影响，从而为利用痕量氢设备进行断层氢气观测提供参考依据。实验结果表明：①取气深度越浅，观测到的氢气浓度越高，日变化幅度越大；②集气管内氢气浓度偏低时，抽气时间设置略高于导气管路排空时间，氢气浓度明显变化，否则变化不明显。  相似文献