Bidirectional loading hybrid tests of square cross‐sections of steel bridge piers

Steel rectangular section columns with stiffened plates are commonly used for elevated highway bridges in the urban areas of Japan. The seismic design of bridge piers is usually performed by dynamic analysis in the horizontal direction using various independent directional seismic acceleration data. However, this simple treatment does not reflect the effect of bilateral loading as a structural response to inelastic interaction. In this study, unidirectional and bidirectional loading hybrid tests were conducted to examine the seismic response and performance of square cross‐sections of steel bridge piers subjected to bidirectional seismic accelerations. Comparison of the results of unidirectional and bidirectional loading tests revealed that the maximum load is the same as the average of unidirectional loading in the NS and EW directions; however, the maximum response displacement and residual displacement increase in proportion with hard to soft ground types. Moreover, a modified seismic design is proposed considering these bidirectional loading effects. Copyright © 2012 John Wiley & Sons, Ltd.     

Performance Analysis of the Effects of Microgrooved Surface on A Marine Current Turbine with Underwater Mooring Platform

China Ocean Engineering - Marine current turbine (MCT), which is designed for the power supply of underwater mooring platform (UMP), is investigated in this article. To reduce its flow noise, the...     

Effects of Social Learning on Rural Farmers’ Adaptive Capacity: Empirical Insights from the Vietnamese Mekong Delta

Abstract

Environmental challenges in the Vietnamese Mekong Delta characterized by adverse impacts of climate change, upstream hydropower development and localized dyke expansion present imperatives for rural farmers to “learn to adapt.” However, little is known about how learning contributes to improving their capacity in adapting to these “wicked” problems. This study investigates potential effects of farmers’ learning on their adaptive capacity, utilizing nine focus group discussions, 33 interviews, and a structured survey of 300 farmers. The exploratory factor analysis produced two factors for social learning: (1) learning through social interactions and (2) self-reflection, and one factor for adaptive capacity. The regression results show that the social learning factors have significantly positive effects on adaptive capacity. Farmers with a higher level of social learning are likely to demonstrate higher adaptive capacity. The findings call for policy considerations to promote learning in a broader context of the delta to enhance local capacity.     

Dynamic positioning configuration and its first-order optimization

Traditional geodetic network optimization deals with static and discrete control points. The modern space geodetic network is, on the other hand, composed of moving control points in space (satellites) and on the Earth (ground stations). The network configuration composed of these facilities is essentially dynamic and continuous. Moreover, besides the position parameter which needs to be estimated, other geophysical information or signals can also be extracted from the continuous observations. The dynamic (continuous) configuration of the space network determines whether a particular frequency of signals can be identified by this system. In this paper, we employ the functional analysis and graph theory to study the dynamic configuration of space geodetic networks, and mainly focus on the optimal estimation of the position and clock-offset parameters. The principle of the D-optimization is introduced in the Hilbert space after the concept of the traditional discrete configuration is generalized from the finite space to the infinite space. It shows that the D-optimization developed in the discrete optimization is still valid in the dynamic configuration optimization, and this is attributed to the natural generalization of least squares from the Euclidean space to the Hilbert space. Then, we introduce the principle of D-optimality invariance under the combination operation and rotation operation, and propose some D-optimal simplex dynamic configurations: (1) (Semi) circular configuration in 2-dimensional space; (2) the D-optimal cone configuration and D-optimal helical configuration which is close to the GPS constellation in 3-dimensional space. The initial design of GPS constellation can be approximately treated as a combination of 24 D-optimal helixes by properly adjusting the ascending node of different satellites to realize a so-called Walker constellation. In the case of estimating the receiver clock-offset parameter, we show that the circular configuration, the symmetrical cone configuration and helical curve configuration are still D-optimal. It shows that the given total observation time determines the optimal frequency (repeatability) of moving known points and vice versa, and one way to improve the repeatability is to increase the rotational speed. Under the Newton’s law of motion, the frequency of satellite motion determines the orbital altitude. Furthermore, we study three kinds of complex dynamic configurations, one of which is the combination of D-optimal cone configurations and a so-called Walker constellation composed of D-optimal helical configuration, the other is the nested cone configuration composed of n cones, and the last is the nested helical configuration composed of n orbital planes. It shows that an effective way to achieve high coverage is to employ the configuration composed of a certain number of moving known points instead of the simplex configuration (such as D-optimal helical configuration), and one can use the D-optimal simplex solutions or D-optimal complex configurations in any combination to achieve powerful configurations with flexile coverage and flexile repeatability. Alternately, how to optimally generate and assess the discrete configurations sampled from the continuous one is discussed. The proposed configuration optimization framework has taken the well-known regular polygons (such as equilateral triangle and quadrangular) in two-dimensional space and regular polyhedrons (regular tetrahedron, cube, regular octahedron, regular icosahedron, or regular dodecahedron) into account. It shows that the conclusions made by the proposed technique are more general and no longer limited by different sampling schemes. By the conditional equation of D-optimal nested helical configuration, the relevance issues of GNSS constellation optimization are solved and some examples are performed by GPS constellation to verify the validation of the newly proposed optimization technique. The proposed technique is potentially helpful in maintenance and quadratic optimization of single GNSS of which the orbital inclination and the orbital altitude change under the precession, as well as in optimally nesting GNSSs to perform global homogeneous coverage of the Earth.     

Response of artificial grassland carbon stock to management in mountain region of Southern Ningxia,China

Grassland is a major carbon sink in the terrestrial ecosystem. The dynamics of grassland carbon stock profoundly influence the global carbon cycle. In the published literatures so far, however, there are limited studies on the long-term dynamics and influential factors of grassland carbon stock, including soil organic carbon. In this study, spatial-temporal substitution method was applied to explore the characteristics of Medicago sativa L.(alfalfa) grassland biomass carbon and soil organic carbon density(SOCD) in a loess hilly region with different growing years and management patterns. The results demonstrated that alfalfa was the mono-dominant community during the cutting period(viz. 0–10 year). Community succession began after the abandonment of alfalfa grassland and then the important value of alfalfa in the community declined. The artificial alfalfa community abandoned for 30 years was replaced by the S. bungeana community. Accordingly, the biomass carbon density of the clipped alfalfa showed a significant increase over the time during 0–10 year. During 0–30 year, the SOCD from 0–100 cm of the soil layer of all 5 management patterns increased over time with a range between 5.300 ± 0.981 kg/m2 and 12.578 ± 0.863 kg/m2. The sloping croplands had the lowest SOCD at 5.300 ± 0.981 kg/m2 which was quite different from the abandoned grasslands growing for 30 years which exhibited the highest SOCD with 12.578 ± 0.863 kg/m2. The ecosystem carbon density of the grassland clipped for 2 years increased 0.1 kg/m2 compared with the sloping cropland, while that of the grassland clipped for 10 years substantially increased to 10.30 ± 1.26 kg/m2. Moreover, the ecosystem carbon density for abandoned grassland became 12.62 ± 0.50 kg/m2 at 30 years. The carbon density of the grassland undisturbed for 10 years was similar to that of the sloping cropland and the grassland clipped for 2 years. Different management patterns imposed great different effects on the accumulation of biomass carbon on artificial grasslands, whereas the ecosystem carbon density of the grassland showed a slight increase from the clipping to abandonment of grassland in general.     

Spectral response of different eroded soils in subtropical china: A case study in Changting County,China

Hyper-spectral data is widely used to determine soil properties. However, few studies have explored the soil spectral characteristics as response to soil erosion. This study analysed the spectral response of different eroded soils in subtropical China, and then identify the spectral characteristics and soil properties that better discriminate softs with different erosion degrees. Two methods were compared： direct identification by inherent spectral characteristics and indirect identification by predictions of critical soft properties. Results showed that the spectral curves for different degrees of erosion were similar in morphology, while overall reflectance and characteristics of specific absorption peaks were different. When the first method is applied, some differences among different eroded groups were found by integration of associated indicators. However, the index of such indicators showed apparent mixing and crossover among different groups, which reduced the accuracy of identification. For the second method, the correlation between critical soil properties, such as soil organic matter （SOM）, iron and aluminium oxides and reflectance spectra, was analysed. The correlation coefficients for the moderate eroded group were primarily between -0.3 to -0.5, which were worse than the other twogroups. However, the maximum value of R2 was obtained as 0.86 and 0.94 for the non-apparent eroded and the severe group. Furthermore, these two groups also showed some differences in the spectral response of iron complex state （Fep）, Aluminium amorphous state （Alo） and the modelling results for soil organic matter （SOM）. The study proved that it is feasible to identify different degrees of soil erosion by hyperspectral data, and that indirect identification by modelling critical soil properties and reflectance spectra is much better than direct identification. These results indicate that hyper-spectral data may represent a promising tool in monitoring and modelling soil erosion.     

Spatial-temporal characteristics of land subsidence corresponding to dynamic groundwater funnel in Beijing Municipality,China

Due to long-term over-exploitation of groundwater in Beijing Municipality,regional groundwater funnels have formed and land subsidence has been induced.By combining a groundwater monitoring network,GPS monitor-ing network data,radar satellite SAR data,GIS and other new technologies,a coupled process model based on the dy-namic variation of groundwater and the deformation response of land subsidence has been established.The dynamic variation of groundwater funnels and the land subsidence response process were analyzed systematically in Beijing.Study results indicate that current groundwater funnel areas are distributed mainly in the southwest of Shunyi District,the northeast of Chaoyang District and the northwest of Tongzhou District,with an average decline rate of groundwa-ter level of 2.66 m/yr and a maximum of 3.82 m/yr in the center of the funnels.Seasonal and interannual differences exist in the response model of land subsidence to groundwater funnels with uneven spatial and temporal distribution,where the maximum land subsidence rate was about-41.08 mm/yr and the area with a subsidence rate greater than 30 mm/yr was about 1637.29 km2.Although a consistency was revealed to exist between a groundwater funnel and the spatial distribution characteristics of the corresponding land subsidence funnel,this consistency was not perfect.The results showed that the response model of land subsidence to the dynamic variation of groundwater was more revealing when combining conventional technologies with InSAR,GIS,GPS,providing a new strategy for environmental and hydrogeological research and a scientific basis for regional land subsidence control.     

http://www.sciencedirect.com/science/article/pii/S1674987112001260

Archaea have unique glycerol dialkyl glycerol tetraether (GDGT) lipids that can be used to develop paleotemperature proxies such as TEX₈₆. This research is to validate proposed GDGT-proxies for paleotemperature determination in the South China Sea (SCS). Samples were collected from core-top sediments (0–5 cm) in the northern SCS. Total lipids were extracted to obtain core GDGTs, which were identified and quantified using liquid chromatography-mass spectrometry (LC-MS). The abundance of isoprenoidal GDGTs (iGDGTs) ranged from 271.5 ng/g dry sediment to 1266.3 ng/g dry sediment, whereas the branched GDGTs (bGDGTs), supposedly derived from terrestrial sources, ranged from 22.2 ng/g dry sediment to 56.7 ng/g dry sediment. The TEX₈₆-derived sea surface temperatures ranged from 20.9 °C in the coast (water depth < 160 m) to 27.9 °C offshore (water depth > 1000 m). TEX₈₆-derived temperatures near shore (<160 m water depth) averaged 23.1 ± 2.5 °C (n = 4), which were close to the satellite-derived winter mean sea surface temperature (average 22.6 ± 1.0 °C, n = 4); whereas the TEX₈₆-derived temperatures offshore averaged 27.4 ± 0.3 °C (n = 7) and were consistent with the satellite mean annual sea surface temperature (average 26.8 ± 0.4 °C, n = 7). These results suggest that TEX₈₆ may record the sea surface mean annual temperature in the open ocean, while it likely records winter sea surface temperature in the shallower water.     

雷达资料在江淮流域暴雨数值模拟中的应用

将雷达资料计入ＰＳＵ／ＮＣＡＲ中尺度模式，对江淮流域暴雨实例进行了模拟实验、在工作中，雷达资料经过处理加入到模式中，改变初始湿度场分析，然后作２４小时数值模拟，并与控制试验作比较。结果表明：加入雷达资料后的数值模拟预报，由于增强了暴雨区及其邻近区域对流层中低层水汽和辐合上升运动，雨区位置和雨量中心值比控制试验更接近实况。     

矩阵扰动分析及其在大地测量反演误差分析中的应用

介绍了矩阵扰动分析的基本理论和方法。提出了利用矩阵的条件数作为大地测量反演误差分析的一个指标，并结合实例论述了利用矩阵的条件数判断反演问题病态特征的方法。指出：在大地测量反演中，可以通过矩阵扰动分析的理论来研究大地测量反演解的特征，从而对反演结果给出恰当的评价。