Distribution of Fe among octahedral sites and its effect on the crystal structure of pumpellyite

Two pumpellyites with the general formula W ₈ X ₄ Y ₈ Z ₁₂O_56-n (OH) _n were studied using ⁵⁷Fe Mössbauer spectroscopic and X-ray Rietveld methods to investigate the relationship between the crystal chemical behavior of iron and structural change. The samples are ferrian pumpellyite-(Al) collected from Mitsu and Kouragahana, Shimane Peninsula, Japan. Rietveld refinements gave Fe(X):Fe(Y) ratios (%) of 41.5(4):58.5(4) for the Mitsu pumpellyite and 46(1):54(1) for the Kouragahana pumpellyite, where Fe(X) and Fe(Y) represent Fe content at the X and Y sites, respectively. The Mössbauer spectra consisted of two Fe²⁺ and two Fe³⁺ doublets for the Mitsu pumpellyite, and one Fe²⁺ and two Fe³⁺ doublets for the Kouragahana pumpellyite. In terms of the area ratios of the Mössbauer doublets and the Fe(X):Fe(Y) ratios determined by the Rietveld refinements, Fe²⁺(X):Fe³⁺(X):Fe³⁺(Y) ratios are determined to be 22:14:64 for the Mitsu pumpellyite and 27:8:65 for the Kouragahana pumpellyite. By applying the Fe²⁺:Fe³⁺-ratio determined by the Mössbauer analysis and the site occupancies of Fe at the X and Y sites given by the Rietveld method together with chemical analysis, the resulting formula of the Mitsu and Kouragahana pumpellyites are established as Ca₈(Fe _0.88 ²⁺ Mg_0.68Fe _0.77 ³⁺ Al_1.66)_Σ3.99(Al_5.67Fe _2.34 ³⁺ )_Σ8.01Si₁₂O_42.41(OH)_13.59 and Ca₈(Mg_1.24Fe _0.65 ²⁺ Fe _0.46 ³⁺ Al_1.66)_Σ4.01(Al_6.71Fe _1.29 ³⁺ )_Σ8.00Si₁₂O_42.14(OH)_13.86, respectively. Mean Y–O distances and volumes of the YO₆ octahedra increase with increasing mean ionic radii, i.e., the Fe³⁺→Al substitution at the Y site. However, change of the sizes of XO₆ octahedra against the mean ionic radii at the X site is not distinct, and tends to depend on the volume change of the YO₆ octahedra. Thus, the geometrical change of the YO₆ octahedra with Fe³⁺→Al substitution at the Y site is essential for the structural changes of pumpellyite. The expansion of the YO₆ octahedra by the ionic substitution of Fe³⁺ for Al causes gradual change of the octahedra to more symmetrical and regular forms.     

Correction: Impact of excessive groundwater pumping on rejuvenation processes in the Bandung basin (Indonesia) as determined by hydrogeochemistry and modeling

In the Bandung basin, Indonesia, excessive groundwater pumping caused by rapid increases in industrialization and population growth has caused subsurface environmental problems, such as excessive groundwater drawdown and land subsidence. In this study, multiple hydrogeochemical techniques and numerical modeling have been applied to evaluate the recharge processes and groundwater age (rejuvenation). Although all the groundwater in the Bandung basin is recharged at the same elevation at the periphery of the basin, the water type and residence time of the shallow and deep groundwater could be clearly differentiated. However, there was significant groundwater drawdown in all the depression areas and there is evidence of groundwater mixing between the shallow and deep groundwater. The groundwater mixing was traced from the high dichlorodifluoromethane (CFC-12) concentrations in some deep groundwater samples and by estimating the rejuvenation ratio (R) in some representative observation wells. The magnitude of CFC-12 concentration, as an indicator of young groundwater, showed a good correlation with R, determined using ¹⁴C activity in samples taken between 2008 and 2012. These correlations were confirmed with the estimation of vertical downward flux from shallower to deeper aquifers using numerical modeling. Furthermore, the change in vertical flux is affected by the change in groundwater pumping. Since the 1970s, the vertical flux increased significantly and reached approximately 15% of the total pumping amount during the 2000s, as it compensated the groundwater pumping. This study clearly revealed the processes of groundwater impact caused by excessive groundwater pumping using a combination of hydrogeochemical methods and modeling.

     

Application of Continuous 222Rn Monitor with Dual Loop System in a Small Lake

To estimate the spatial distribution of groundwater discharge from the bottom of a small lake of Kumamoto in Japan, we applied continuous radon measurements with a dual loop system and verified the results obtained using the radon method by visual diving surveys. Time‐shifting correction in the dual‐loop system is reasonable to obtain the true radon activity in water. Distributions of radon activity and water temperature in the study area reveal the effects on groundwater discharge and mixing situation of lake water. The estimated discharge zone ascertained using the radon method agrees with the groundwater discharge distribution observed through diving surveys. Although the data resolution of the radon method is much greater than the width of observed discharge zones, the general distribution of groundwater discharge is recognizable. The dual loop system of radon measurement is useful for smaller areas.     

Origin of the Velocity-Strengthening Nature of Granular Friction

A simple theory for a constitutive law for steady state dynamic friction in granular matter is presented. Starting from the energy balance equation together with the kinetics of grains, the energy dissipation rate is estimated, which directly leads to a constitutive law. The result indicates that a system of lower density is stronger than a system of higher density, albeit somewhat counterintuitive. This is a consequence of the fact that the grain rearrangement, which causes energy dissipation, is more frequent in a system of lower density. Thus, the velocity-strengthening nature of granular friction is naturally explained by the negative shear-rate dependence of the density. The present theory also qualitatively explains the experimental observation that a system of smaller layer thickness tends to be velocity-weakening.     

Hydraulic model tests for evaluating sediment control function with a grid-type Sabo dam in mountainous torrents

There are two kinds of Sabo dams in order to control sediment transport by debris flow and flash floods in mountainous area, which are closed and open-type＇s dams. In Japan, open-type＇s Sabo dams are constructed taking into account the continuity of sediment routing from upstream to downstream reach in a basin. A plan to construct a 20 m high grid-type Sabo dam which can capture a sediment volume of 400,000 m3 is proposed in the Amahata river basin in Japan. Hydraulic model tests are conducted to decide on the section for a dam （Section A, B） and the grid size such as clearance of vertical/horizontal bars for evaluating the plan. Several runs of flume tests are conducted and the sediment control function of the Sabo darn is discussed using several experimental data such as dimensionless sediment runoff rate from Sabo dam, temporal changes of bed profile and mean diameter and so on. It was found that sediment deposition in sediment storage area of Sabo dam was affected by curved channel, and that next the grid size of steel bars and thirdly the section of a dam was able to capture sediment in storage area of Sabo dam. Sediment was controlled well in the section B and in the grid size of 1.0×d95, and the problems related to sediment runoffafter sediment capturing in Sabo dam are pointed out.     

Spatial variability and correlation of environmental proxies during the past 18,000 years among multiple cores from Lake Pumoyum Co,Tibet, China

Multiple cores from Lake Pumoyum Co, southern Tibet, provide an improved understanding of the spatial distribution of lake sediments, and how well they represent the paleo-climate. Comparative study of these cores using AMS ¹⁴C dating and environmental proxies clarified their relationships with environmental changes. Our work focused on understanding the spatial similarities among cores covering different time scales, and evaluating variations in sedimentary processes across sites. The four studied cores demonstrate different sedimentation rates, but environmental proxies help synchronize the timing of environmental variations. Sediment variables such as total organic carbon (TOC), inorganic carbon (IC), and grain size in different cores correlate well and corroborate changing trends over the past 10,000 cal years. Differences in sedimentation rates and facies among core sites probably result largely from differences in water depth. The core from the deepest site displays the highest average sedimentation rates and the highest accumulation rates of TOC, but lowest content of IC. Two cores from somewhat shallower sites have plant residues in their lower sections and record similar variations in both the number of layers and their depositional ages. Our results do not indicate any significant variation in sedimentation pattern or its related factors among the three sites. A single core from the deepest site could adequately represent the total lake environment over the time span covered. But cores from somewhat shallower sites might reveal important shifts in the environment over a longer time period.     

关于地铁地震响应的模型振动试验及数值分析

为明确大地震时地铁的破坏过程及原因,以1995 年日本阪神－淡路大地震中遭受严重破坏的神户大开地铁车站为对象,进行了一系列的模型振动试验和动力有限元分析。对于作用于地下结构的地震动土压的发生原理、地震波输入方向、结构的埋设深度、地基与结构间的刚性比对地震动土压的影响及在地基-结构系统的非线性响应下结构周围地基终局状态时的地震动土压进行了研究。明确了地震动土压的极限值及在大地震时周围地基的残余应变引起的静止土圧力的存在。为今后改进地震土压力计算方法、提高地下结构抗震设计水平提供了依据。