Rock Strength and Development of Glacial Valley Morphology in the Scottish Highlands and Northwest Iceland

Using data from the Scottish Highlands and northwest Iceland, the present study indicates that bedrock strength properties are an important control on the morphology of glacial valleys. Results indicate that on closely jointed metasedimentary bedrock of low rock mass strength, broad U‐shaped valleys are developed, whilst steeper sided, narrower cross‐profiles have been developed on igneous bedrock of high rock mass strength. Findings suggest it is the interplay of the mass strength of the subglacial bedrock and the dynamic properties of the eroding glacier that control valley morphological development. The implication is that realistic models of topographic development beneath ice sheets need to consider the rock mass strength properties of the eroded bedrock as well as the glaciological variables.     

Mechanisms of compaction of quartz sand at diagenetic conditions

The relative contribution of cracking, grain rearrangement, and pressure solution during experimental compaction of quartz sand at diagenetic conditions was determined through electron and optical microscopy and image analysis. Aggregates of St. Peter sand (255±60 μm diameter grain size and porosity of approximately 34%) were subjected to creep compaction at effective pressures of 15, 34.5, 70, and 105 MPa, temperatures of 22 and 150°C, nominally dry or water-saturated (pore fluid pressure of 12.5 MPa) conditions, and for times up to one year. All aggregates displayed transient, decelerating creep, and volume strain rates as low as 2×10⁻¹⁰ s⁻¹ were achieved. The intensity of fracturing and degree of fragmentation increase with volume strain and have the same dependence on volume strain at all conditions tested, indicating that impingement fracturing and grain rearrangement were the main mechanisms of compaction throughout the creep phase. The increase in fracture density and decrease in acoustic emission rate at long times under wet conditions reflect an increase in the contribution of subcritical cracking. No quantitative evidence of significant pressure solution was found, even for long-term creep at 150°C and water-saturated conditions. Comparison of our findings to previous work suggests that pressure solution could become significant at temperatures or times somewhat greater than investigated here.     

如何使用Excel电子表格编制土壤水分测定工作表

土壤水分测定是农业气象观测员的一项重要业务之一。随着近年来计算机的快速发展，我们对此项工作从20世纪90年代初就开始使用计算机来编制程序，从开始的PC-1500到目前的个人电脑，从BASIC语言（在DOS下运动）到现在的集成大型办公软件（如：Office2000），土壤水分测定计算越来越准确，越来越方便，深受农气测报观测员的喜爱。     

Antarctic environmental variability since the late Miocene: ODP Site 745, the East Kerguelen sediment drift

Characterization of sediment from Ocean Drilling Program Site 745, representing the East Kerguelen Ridge sediment drift, addresses important issues surrounding the timing of Miocene to present East Antarctic ice sheet stability and oceanic environmental change. Our results show three periods of greatly enhanced accumulation of Antarctic-derived sediment, at 6.4-5.9 Ma, 4.9-4.4 Ma and 1.1-0.8 Ma, potentially indicative of warmer, less stable ice sheets at these times. Conversely, the accumulation of Antarctic-derived material is comparatively less during the middle of the Pliocene warm epoch (4.8-3.2 Ma). The deep flow forming the Kerguelen drift was stronger during the latest Miocene and earliest Pliocene and has decreased in intensity continuously since then.     

用碳纤维布改善钢筋混凝土极短柱抗震性能的试验研究

本文进行了5根钢筋混凝土极短柱（λ=1.0）在周期反复荷载作用下的试验，研究了使用碳纤维布横向包裹钢筋混凝土极短柱以提高其延性这种加固方法的有效性。本文研究了碳纤维布横向包裹钢筋混凝土极短柱的受力特性，分析了碳纤维布抗拉强度对试件抗震性能的影响，并对碳纤维布加固钢筋混凝土极短柱使其延性提高的机理进行了探讨。试验结果表明，横向包裹碳纤维布可显著提高钢筋混凝土极短柱的变形性能。     

磁尾地向传播等离子体团的模拟研究

卫星观测证实了磁尾等离子体团与亚暴活动的相关性,除了具有北-南双极特征的尾向传播等离子体团外,还发现地向传播等离子体团,它们表现为南-北双极中性片事件和南-北双极瓣区讯号. 资料分析表明:南-北双极讯号的出现几率远低于北-南双极讯号,并且南-北双极事件主要发生于行星际磁场北向和地磁宁静条件,它们往往与小的孤立的地磁亚暴相关. 本文根据地磁宁静时期(IMF Bz北向且By≥Bz)越尾电场Ey分量的分布特点,对地向传播等离子体团作模拟研究. 两类算例的数值结果展示了通量绳磁结构及具有复杂闭合磁力线位形的等离子体团的基本特征,上述特征与尾向传播的等离子体团类似,与IMP 8卫星关于地向传播南-北中性片事件的观测特征大致相符. 数值结果还展示了与Schindler示意图相类似的磁力线拓扑位形,在一定程度上为南-北事件出现几率低作出了解释;并且揭示了磁尾中性片内越尾磁场分量By对磁重联发展的抑制作用. 本文的模拟研究说明:无论磁尾处于活动时期(IMF Bz为南向),还是宁静时期(IMF Bz为北向且By≥Bz),磁场重联均是磁尾等离子体加速和加热的通用机制.     

Pore-throat size distributions in Permo-Triassic sandstones from the United Kingdom and some implications for contaminant hydrogeology

Pore-throat size distributions (PSDs) from mercury injection capillary pressure (MICP) tests have been used to characterise 153 samples of Permo-Triassic sandstones from the United Kingdom. The PSDs have been parameterised using the Brooks-Corey and van Genuchten functions. Pore-throat sizes are in the range 0.01–427 μm, and dominant pore-throat sizes range from about 0.1–90 μm. Values of λ, the Brooks-Corey pore-size distribution index, range from 0.002–2.27, and values of m, the van Genuchten pore-size distribution index, range from 0.03–0.92. A number of classes of sandstone can be recognised on the basis of trends in the fitted parameters. The van Genuchten function provides the most effective method for classifying different sandstones. Additionally, a cross-plot of gas permeability against displacement pressure (derived from the van Genuchten function) shows that the data fall into two distinct sub-populations. The frequency distribution of a larger population of sandstone permeabilities can be modelled using the mean and standard deviation of the two sub-populations identified in the MICP study, assuming that the sub-populations are approximated by log-normal distributions. The distribution of sandstones with small pore-throat sizes is critical to the fate of pathogens and immiscible phase contaminants in the aquifer. Electronic Publication     

大尺度弯曲波和木星磁盘的波状结构

本文提出,术星磁盘的波状结构可能是由木星等离子体片中存在的大尺度弯曲波引起的。从磁流体力学方程组出发,建立了一个自洽的稳态木星磁盘模式,在这个模式中包括了径向等离子体流和方位角方向的磁场。利用扰动的磁流体力学方程组,得出了普遍的色散方程。在某些简化条件下解出了色散关系。结果表明,弯曲波是一种新型的耦合波,即Alfvèn波和旋转波（频率相当于木星的旋转角速度Ω_J）相耦合的新型波。这种波的特性与等离子体片的结构相关。根据这种波的特征函数,给出了木星磁盘波状结构的表达式,理论结果与根据探测数据得出的经验形式相符。     

EM induction in the Vancouver Island region: 3D numerical,analogue model,and field site results

Electromagnetic induction in the Vancouver Island region for a uniform inducing source field for 300 s period is investigated with the aid of three-dimensional (3-D) numerical and analogue model results and field site measurements. The thin sheet numerical model, based on the subducting Juan de Fuca plate analogue model ofDosso et al., consists of a 5km thick non-uniform thin sheet (comprising the lateral conductivity contrasts arising from the land, the varying depth ocean, and the sediment) underlain by a four-layer conductive structure. The four-layer conductive structure beneath the non-uniform thin sheet simulates the effect of the Juan de Fuca plate subducting Vancouver Island. To examine the effects of the ocean channel depth between Vancouver Island and the British Columbia (Canada) mainland, numerical results were obtained for two channel depths (0 and 600 m). The results indicate that the channel plays an important role in the geomagnetic response in the central and inner coastal regions of Vancouver Island. The general agreement of the 3-D numerical model induction arrows with the analogue model and field site induction arrows for 300 s supports the premise of a layered conductive substructure dipping at a small angle, at most, beneath Vancouver Island.Lithoprobe Publication No. 311.     

磁尾电流片撕裂模时间演化的非线性性态

本文运用摄动法解析地研究了磁尾电流片平板模型非线性撕裂模的时间演化及与晨昏电场的相互作用.结果表明,撕裂模的非线性时间演化最终会形成磁岛,磁岛宽度与扰动增长率的四次方根成正比;在扰动晨昏电场的作用下,磁岛宽度可发生尖点突变,尖点突变临界值所对应的晨昏电场扰动幅值约为5mV/m,这与磁亚暴发生时晨昏电场的幅值对应.