Collisional disruption experiments of porous targets

More and more small bodies are found to be porous. Laboratory impact experiments of various porous materials have been performed, which increased our understanding of the impact process of porous bodies. In this review, we classify porous targets according to the internal structure, describe the physical properties that characterize these materials, and summarize some results of impact strength and the general tendency upon impact condition and material properties. The material property presented here includes a relation between applied load and distension although measured in static condition. Further investigation is required to clarify the role of crack growth and compaction in the time evolution of physical properties of porous materials upon impact. Laboratory experiments with detailed material properties will be useful as a database that can serve as a reference for numerical modeling and theoretical scaling considerations.     

Radiative lifetimes and transition probabilities in Hf I and Hf III

Radiative lifetimes of nine odd levels in Hf III (5d6p z³P_0,1, z¹D₂, z³D_1,2,3, z³F_2,3,4) and of two odd levels in Hf I (5d6s²6p z³D_2,3) have been determined using Time-Resolved Laser-Induced Fluorescence. The investigated levels in Hf I were excited in a single-step process from the ground term (5d²6s² a³F), whereas in Hf III we started from either the ground term 5d² a³F or the low-lying 5d6s a³D term. For all of the investigated levels, the lifetimes have been measured for the first time. A multiconfiguration relativistic Hartree–Fock method, including core-polarization effects, has been used to compute radiative lifetimes of 15 Hf III levels, including those measured in this work. Transition probabilities for 55 transitions in Hf III are also given.     

Dust formation and evolution in a Ca–Fe–SiO–H2–O2 vapour phase condensation experiment and astronomical implications

Here, we report on a kinetically controlled vapour phase condensation experiment using a low-calcium Ca–Fe–SiO–H₂–O₂ vapour. Under these conditions of extreme disequilibrium, the condensate properties become predictable. They are amorphous solids with (predictable) deep metastable eutectic compositions. This study also shows how chemical evolution of the condensate grains will lead to chemically complex amorphous solids. The highly disordered structure of the deep metastable eutectic condensates is the very key to this predictable chemical evolution to grains with a silicate mineral composition, yet being amorphous. We compare our results with astronomical observations of dust around young stellar objects.     

Retardation capacity of altered granitic rock distributed along fractured and faulted zones in the orogenic belt of Japan

There are wide areas of granitic rocks in the Japanese orogenic belt. These granitic bodies inevitably contain fracture and fault systems associated with alteration zones. However, relatively little attention has been given to the possible influence of such widely distributed alteration zones on the migration of radionuclides from any radioactive waste repository that might in future be sited within granitic rock. In particular, the influences of alteration products and micro-fractures, due to chemical sorption and/or physical retardation require further consideration. In order to understand the retardation capacity of the altered deep granitic rocks, detailed geometrical characterization of pores, geochemical analysis, and batch sorption and flow-through experiments have been carried out. Those results show that the altered granite has a large volume of accessible pores, particularly in potassium-feldspar grains, which would influence nuclide retardation more than the accessible porosity in other minerals present, such as biotite. The distribution coefficients, Kd estimated from batch sorption tests and flow-through experiments suggest that altered granite has a high capability to retard the migration of nuclides. The retardation would probably be due to sorption on altered minerals such as sericite and iron hydroxides formed along grain boundaries and in pores created by dissolution, in addition to sorption on primary sorptive minerals. These results provide confidence that even altered and fractured parts of any granitic rock that might be encountered in a site for the disposal of high level radioactive waste may still retard radionuclide migration and thereby help the geosphere to function as a barrier.     

Breakdown of hydrous ringwoodite to pyroxene and spinelloid at high P and T and oxidizing conditions

To get deeper insight into the phase relations in the end-member system Fe₂SiO₄ and in the system (Fe, Mg)₂SiO₄ experiments were performed in a multi-anvil apparatus at 7 and 13 GPa and 1,000–1,200°C as a function of oxygen fugacity. The oxygen fugacity was varied using the solid oxygen buffer systems Fe/FeO, quartz–fayalite–magnetite, MtW and Ni/NiO. The run products were characterized by electron microprobe, Raman- and FTIR-spectroscopy, X-ray powder diffraction and transmission electron microscopy. At fO₂ corresponding to Ni/NiO Fe-ringwoodite transforms to ferrosilite and spinelloid according to the reaction: 9 Fe₂SiO₄ + O₂ = 6 FeSiO₃ + 5 Fe_2.40Si_0.60O₄. Refinement of site occupancies in combination with stoichiometric Fe³⁺ calculations show that 32% of the total Fe is incorporated as Fe³⁺ according to From the Rietveld refinement we identified spl as spinelloid III (isostructural with wadsleyite) and/or spinelloid V. As we used water in excess in the experiments the run products were also analyzed for structural water incorporation. Adding Mg to the system increases the stability field of ringwoodite to higher oxygen fugacity and the spinel structure seems to accept higher Fe³⁺ but also water concentrations that may be linked. At oxygen fugacity corresponding to MtW conditions similar phase relations in respect to the breakdown reaction in the Fe-end-member system were observed but with a strong fractionation of Fe into spl and Mg into coexisting cpx. Thus, through this strong fractionation it is possible to stabilize very Fe-rich wadsleyite with considerable Fe³⁺ concentrations even at an intermediate Fe–Mg bulk composition: assuming constant K _D independent on composition and a bulk composition of x _Fe = 0.44 this fractionation would stabilize spl with x _Fe = 0.72. Thus, spl could be a potential Fe³⁺ bearing phase at P–T conditions of the transition zone but because of the oxidizing conditions and the Fe-rich bulk composition needed one would expect it more in subduction zone environments than in the transition zone in senso stricto.

室内模拟试验确定横向扩散系数的研究--以吉林市第二松花江某江段为例

确定河流横向扩散系数的主要方法有经验公式法和河流示踪试验法.以室内模拟试验求横向扩散系数的方法是一种新的尝试,采用几何相似原理,通过不同流量、流速条件下的室内模拟试验,计算出与河流相应条件下的横向扩散系数,所得结果(0.086 m2/s)与同条件下现场分析计算的结果(0.079～0.088 m2/s)基本一致.模拟试验不仅克服了野外条件下示踪剂投放和测试条件的不便,还能够更好地研究不同水动力条件下污染物的扩散运移规律.     

断裂熔融作用中单质铁的形成及其指示的孕震环境

目前缺乏来自于地震断裂带的假玄武玻璃的原始特征研究,制约着我们对地震孕震环境和地震发生机制的认识。本文以龙门山断裂带汶川科钻2号钻孔岩心的碎裂岩及花岗闪长岩为研究对象,通过氩气环境下的高温加热实验(最高温度达1750℃)、显微结构观察、地球化学分析和岩石磁学测试,探讨断裂熔融作用中单质铁的形成及其指示意义。花岗闪长岩和碎裂岩在1100℃时发生部分熔融作用,形成了非晶质和微晶;在≥1300℃时形成了大量单质铁组成的微球粒,可能是含铁矿物发生了以碳物质为还原剂的高温还原反应。高温实验后样品的磁化率值高于碎裂岩的磁化率值,新生成的磁铁矿是≤1100℃的样品高磁化率值的主要原因;熔融作用中形成的单质铁和少量的磁铁矿是≥1300℃样品高磁化率值的重要原因。结合前人对于快速摩擦实验熔体、地幔物质及陨石的研究,我们认为粘土矿物、硅酸盐矿物含量较多的断层泥在同震滑移中因热增压机制很难形成单质铁;而花岗岩、安山岩、辉长岩、闪长岩等岩浆岩和糜棱岩在流体作用弱和硫化物含量低的环境中易在大地震中形成单质铁。龙门山断裂带的假玄武玻璃的熔融温度≥1300℃,硫元素含量较低并发现有过剩铁元素。因此,表明龙门山断裂带的假玄武玻璃中可能形成了单质铁,其和磁铁矿是假玄武玻璃高磁化率值异常的重要原因,并指示了深部流体作用弱、硫化物含量低、还原性的孕震环境。     

Taguchi design-based seismic reliability analysis of geostructures

This paper presents a methodology to evaluate the seismic reliability of geostructures in an optimal way. Taguchi design of experiments are adopted to find the most efficient and cost-effective combination of material properties in the uncertainty domain. Twelve uniform and mixed design models are tested. A polynomial-based response surface meta-model is built for each one and the accuracy of perdition is examined using 10,000 Monte Carlo simulations. A two-dimensional gravity dam is used as a vehicle for probabilistic transient analyses. The ground motion record-to-record variability is added as well using over one hundred earthquake records selected based on probabilistic seismic hazard analysis. Dynamic sensitivity of epistemic random variables are evaluated for the first time. Finally, an efficient and practical procedure is proposed in order to determine the reliability index of the geostructures. This approach, in fact, can be generalised for any type of engineering structures dealing with multi-hazard problems.     

A semi-empirical dilatancy model for ballast fouled with plastic fines

In the era of high speed trains, it is very important to ensure the stability of rail tracks under adverse conditions including the fouling of ballast. Fouling of ballast from unstable and saturated soft subgrade soil is one of the major reasons for track deterioration. The reported results of a number of large-scale laboratory experiments on the shear behaviour of ballast and fouled ballast are analysed, herein. It was observed that fines have a significant influence on the shear behaviour of ballast. Shear strength increases and dilatancy decreases with the addition of fines. In this paper, a semi-empirical mathematical model has been proposed to capture the dilatancy of ballast fouled with fines during shearing. The empirical constants a, b and c proposed in the model are a function of the fines content Void Contamination Index (VCI). The results of the model have been compared with the laboratory experiments and are found to be in good agreement.