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31.
湖泊沉积物碳埋藏及其驱动机制是陆地生态系统碳循环及全球变化研究的热点问题之一,但以往湖泊碳循环的研究大多局限于有机碳,较少考虑无机碳的地位和作用.我国干旱-半干旱地区湖泊众多、无机碳储量丰富,在区域碳循环过程中的作用日益突出,因此探讨这些地区湖泊沉积物无机碳埋藏变化对深入理解区域碳循环具有重要意义.本研究通过对内蒙古高原呼伦湖15个沉积岩芯样品无机碳含量(TIC)的测定,结合沉积岩芯210Pb、137Cs年代标尺,分析了1850年以来呼伦湖无机碳埋藏速率时空变化,并揭示了影响呼伦湖无机碳埋藏的主要因素.结果表明,1980s之前,呼伦湖无机碳含量总体维持在相对稳定的低值,1980s之后开始快速增加,且近百年来呼伦湖平均无机碳含量在不同湖区差异不显著.1850年以来呼伦湖无机碳埋藏速率变化范围约为7.10~74.29 g/(m2·a),平均值约为36.15 g/(m2·a),且大体上可分为3个阶段,即1900s以前相对稳定的低值阶段、1900s-1950s期间的快速增加阶段以及1950s以来的波动增加阶段,各阶段无机碳埋藏速率平均值分别约为10.40、26.29和41.00 g/(m2·a).空间上,呼伦湖无机碳埋藏速率整体表现为中部高、南北两端低的分布格局,这可能与湖心水动力条件相对稳定,有利于碳酸盐沉积有关.此外,呼伦湖无机碳埋藏速率与湖区温度变化呈显著正相关,而与周边人类活动影响关系不明显,表明在未来全球变暖背景下,呼伦湖无机碳埋藏速率将进一步增加,湖泊在区域碳循环中的作用将更加显著. 相似文献
32.
The aim of this work is to model beam‐column behavior in a computationally effective manner, revealing reliably the overall response of reinforced concrete members subjected to intensive seismic loading. In this respect, plasticity and damage are considered in the predominant longitudinal direction, allowing for fiber finite element modeling, while in addition the effect of inelastic buckling of longitudinal rebars, which becomes essential at later stages of intensive cyclic loading, is incorporated. Α smooth plasticity‐damage model is developed for concrete, accounting for unilateral compressive and tensile behavior, nonlinear unloading and crack closure phenomena. This is used to address concrete core crushing and spalling, which triggers the inelastic buckling of longitudinal rebars. For this reason, a uniaxial local stress‐strain constitutive relation for steel rebars is developed, which is based on a combined nonlinear kinematic and isotropic hardening law. The proposed constitutive model is validated on the basis of existing experimental data and the formulation of the buckling model for a single rebar is developed. The cross section of rebar is discretized into fibers, each one following the derived stress‐strain uniaxial law. The buckling curve is determined analytically, while equilibrium is imposed at the deformed configuration. The proposed models for concrete and rebars are embedded into a properly adjusted fiber beam‐column element of reinforced concrete members and the proposed formulation is verified with existing experimental data under intensive cyclic loading. 相似文献
33.
在强震状态下,建筑物的横拉承压受力较为复杂,另外由于建筑物形状及在地震中受力面积大小不同,在强震下造成碰撞大小影响不一导致其横拉承压力的随机复杂性十分突出。传统的建筑承压负荷检测方法中钢筋负荷受力测量能力不足,检测结果易出现误差。将建筑钢筋的机械性能设为理想弹塑性,利用建筑物横拉承压力钢筋负荷测量方法,对不同结构、不同工况的建筑钢筋载荷的变化规律进行测试分析,结合建筑局部承压特点和整体结构聚力方式,设计横拉承压力钢筋负荷检测方法,并进行仿真实验,结果表明该方法模型所得数据更加精准,有良好的适用性。 相似文献
34.
《Limnologica》2020
Aquatic plants are essential for maintaining the diversity and stability of a lake ecosystem. Stable carbon isotopes (δ13C) of macrophytes have been widely used as a powerful tool to study ecological processes and paleoenvironmental evolution in lakes. Varying results are obtained when using the δ13C of macrophytes to study the changes in the lake environment at different spatio-temporal scales. Thus, sample preparation and subsequent laboratory analyses are crucial for studying environmental changes using the isotopic signal retained in the macrophytes, and are essential for the interpretation of isotope-environment relationships. This study analyzed the δ13C of different tissue components of macrophytes in three lakes of the lower Yangtze River basin, and a correlation analysis was performed on aquatic environments influencing the δ13C values in the different tissue components of macrophytes. The test results showed the difference between the δ13C values of the whole sample and cellulose. Relative analyses indicated that the major factors contributing to the δ13C variability in macrophytes were pH and the concentration of dissolved inorganic carbon (DIC). The δ13C of α-cellulose (δ13CAC) is more sensitive to environmental variables than that of the whole sample (δ13CW) and holocellulose (δ13CHC). The results of this study imply that extraction of α-cellulose is a prerequisite for research on the changes in lake environment using δ13C of macrophytes. This study aims to provide theoretical and data basis for further research on the environmental and ecological change using stable carbon isotopes of aquatic plants. 相似文献
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37.
To better understand the mechanisms relating to hydrological regulations of chemical weathering processes and dissolved inorganic carbon (DIC) behaviours, high-frequency sampling campaigns and associated analyses were conducted in the Yu River, South China. Hydrological variability modifies the biogeochemical processes of dissolved solutes, so major ions display different behaviours in response to discharge change. Most ions become diluted with increasing discharge because of the shortened reactive time between rock and water under high-flow conditions. Carbonate weathering is the main source of major ions, which shows strong chemostatic behaviour in response to changes in discharge. Ions from silicate weathering exhibit a significant dilution effect relative to the carbonate-sourced ions. Under high temperatures, the increased soil CO2 influx from the mineralisation of organic material shifts the negative carbon isotope ratios of DIC (δ13CDIC) during the high-flow season. The δ13CDIC values show a higher sensitivity than DIC contents in response to various hydrological conditions. Results from a modified isotope-mixing model (IsoSource) demonstrate that biological carbon is a dominant source of DIC and plays an important role in temporal carbon dynamics. Furthermore, this study provides insights into chemical weathering processes and carbon dynamics, highlighting the significant influence of hydrological variability to aid understanding of the global carbon cycle. 相似文献
38.
Ching-Yi Tsai Keh-Chyuan Tsai Chao-Hsien Li Chung-Che Wu Ker-Chun Lin Sheng-Jhih Jhuang 《地震工程与结构动力学》2020,49(13):1344-1362
Steel box columns are widely used in steel building structures in Taiwan due to their dual strong axes. To transfer the beam-end moment to the column, diaphragm plates of the same thickness and elevations as the beam flanges are usually welded inside the box column. The electro-slag welding (ESW) process is widely used to connect the diaphragms to the column flanges in Taiwan because of its convenience and efficiency. However, ESW may increase the hardness of the welds and heat-affected zones (HAZs), while reducing the Charpy-V notch strength in the HAZ. This situation can cause premature fracture of the diaphragm-to-column flange welds before a large plastic rotation is developed in the beam-to-box column joints. To quantify the critical eccentricity and the effectiveness of fracture prediction, this study uses fracture prediction models and finite element model (FEM) analysis to correlate the test results. In this study, two beam-to-box column connection subassembly tests are conducted with different loading protocols and ESW chamber shapes. To implement a fracture prediction model, the material parameters are established from circumferential notched tensile tests and FEM analysis. Test results indicate that the fracture instances can be predicted on the basis of the cumulative plastic deformation in the HAZs. Analytical results indicate that fracture instances and locations are sensitive to the relative locations of the ESW joints and beam flange. Tests also confirm that the possible fracture of the diaphragm-to-column flange joints can be mitigated by enlarging the chamber of the ESW joint. 相似文献
39.
基于温州市山地丘陵区开展的多目标地球化学调查获得的深、表层土壤有机碳和全碳数据,采用直线模型法计算了研究区表层(0~0.2 m)、中层(0~1.0 m)和深层(0~2 m)土壤无机碳的单位储量及密度;采用指数模型法计算了研究区表层(0~0.2 m)、中层(0~1.0 m)和深层(0~2 m)土壤有机碳的单位储量及密度。利用这些数据分别编制了表层、中层、深层无机碳和有机碳的碳密度图,分析了无机碳、有机碳的分布范围和特点以及它们在不同土壤类型中的分布特征。结果表明研究区单位土壤无机碳平均储量为2881.333t,平均密度为0.720 kg/m^2,单位土壤有机碳平均储量为43128.667t,平均密度为10.782 kg/m^2;有机碳和无机碳在表层、中层和深层土壤中含量分布趋势一致;在不同土壤类型中含量分布趋势也一致,均为滨海岩土中最高,粗骨土中最低。 相似文献
40.
提出一种波纹钢管铅阻尼器,介绍了其构造、工作机理、布置形式及特点,采用ABAQUS软件,建立钢管阻尼器、波纹钢管阻尼器和波纹钢管铅阻尼器有限元模型,对其应力分布,传力路径和滞回性能进行模拟分析。结果表明:波纹钢管铅阻尼器耗能减震机理明确,工作性能和耗能性能稳定,滞回曲线饱满以及耗能能力强,具有良好的变形和延性,极限变形大;波纹钢管铅阻尼器通过在波纹钢管内设置铅芯使初始刚度、承载能力和耗能能力得到大幅度提高,既有效保持了波纹钢管的变形能力,又避免波纹钢管发生局部屈曲,使波纹钢管耗能能力得到充分发挥。波纹钢管铅阻尼器在1mm小位移下就可以进入耗能,而且很快进入稳定耗能状态,等效阻尼比稳定在0.3~0.4之间。 相似文献