The influence of grain-size analysis methods and sediment mixing on curve shapes and textural parameters: Implications for sediment trend analysis

To this day, deterministic physical models capable of explaining the evolution of grain-size distributions in the course of transport are still lacking. For this reason, various attributes of particle frequency distributions, in particular curve shapes and textural parameters, have for many decades been investigated for potential information about transport behaviour and size-sorting processes of sediments in numerous environments. Such approaches are essentially conceptual and hence rely heavily on the validity of the assumptions on which they are based. A factor which has to date been largely ignored in this context, is the fact that different methods of grain-size analysis (e. g. sieving, laser absorption and diffraction, settling velocity measurements), when applied to the same sample material, produce variable curve shapes, and hence incongruous textural data. This is illustrated by selected examples showing the differences between sieving and settling results, conversion of settling velocities into equivalent settling diameters (psi-phi-transformations), and the influences of particle shape, particle density, and water temperature. It is demonstrated that particle-size distributions are not only method-dependent but also dependent on the adopted post-processing procedure. As a result, only frequency curves generated by the same method and subsequently processed by identical computational procedures can be meaningfully compared. Furthermore, the computation of textural parameters from bi- or multimodal size distributions produces spurious results which are unrelated to the processes leading to the mixing of different size populations frequently observed in nature. In such cases, only the decomposition of such distributions into individual populations and the spatial comparison of such populations makes any sense. Because a physical explanation for the generation of size distributions is lacking, a particular curve shape of a grain-size population has no meaning on its own. Only a systematic comparison of progressively changing curve shapes (and associated textural parameters) of sediments collected on a closely spaced grid can yield data suitable for sediment trend analysis.     

EVOLUTIONAL CHARACTERISTICS OF HYPER－CONCENTRATED FLOW IN BRAIDED CHANNEL OF THE YELLOW RIVER

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The Oligocene Lund Tuff, Great Basin, USA: a very large volume monotonous intermediate

Unusual monotonous intermediate ignimbrites consist of phenocryst-rich dacite that occurs as very large volume (>1000 km³) deposits that lack systematic compositional zonation, comagmatic rhyolite precursors, and underlying plinian beds. They are distinct from countless, usually smaller volume, zoned rhyolite–dacite–andesite deposits that are conventionally believed to have erupted from magma chambers in which thermal and compositional gradients were established because of sidewall crystallization and associated convective fractionation. Despite their great volume, or because of it, monotonous intermediates have received little attention. Documentation of the stratigraphy, composition, and geologic setting of the Lund Tuff – one of four monotonous intermediate tuffs in the middle-Tertiary Great Basin ignimbrite province – provides insight into its unusual origin and, by implication, the origin of other similar monotonous intermediates.The Lund Tuff is a single cooling unit with normal magnetic polarity whose volume likely exceeded 3000 km³. It was emplaced 29.02±0.04 Ma in and around the coeval White Rock caldera which has an unextended north–south diameter of about 50 km. The tuff is monotonous in that its phenocryst assemblage is virtually uniform throughout the deposit: plagioclase>quartz≈hornblende>biotite>Fe–Ti oxides≈sanidine>titanite, zircon, and apatite. However, ratios of phenocrysts vary by as much as an order of magnitude in a manner consistent with progressive crystallization in the pre-eruption chamber. A significant range in whole-rock chemical composition (e.g., 63–71 wt% SiO₂) is poorly correlated with phenocryst abundance.These compositional attributes cannot have been caused wholly by winnowing of glass from phenocrysts during eruption, as has been suggested for the monotonous intermediate Fish Canyon Tuff. Pumice fragments are also crystal-rich, and chemically and mineralogically indistinguishable from bulk tuff. We postulate that convective mixing in a sill-like magma chamber precluded development of a zoned chamber with a rhyolitic top or of a zoned pyroclastic deposit. Chemical variations in the Lund Tuff are consistent with equilibrium crystallization of a parental dacitic magma followed by eruptive mixing of compositionally diverse crystals and high-silica rhyolite vitroclasts during evacuation and emplacement. This model contrasts with the more systematic withdrawal from a bottle-shaped chamber in which sidewall crystallization creates a marked vertical compositional gradient and a substantial volume of capping-evolved rhyolite magma. Eruption at exceptionally high discharge rates precluded development of an underlying plinian deposit.The generation of the monotonous intermediate Lund magma and others like it in the middle Tertiary of the western USA reflects an unusually high flux of mantle-derived mafic magma into unusually thick and warm crust above a subducting slab of oceanic lithosphere.     

Sandy gravel accumulation in a fluvial environment

Particle size, pebble shape, pebble fabric, discharge and flow velocity data are used to introduce a model of sandy gravel formation in Welsh gravel-bed rivers. The development of contact-imbrication of the typically very bladed and very platy cobbles and larger pebbles subsequently acts to significantly affect the depositional modes and patterns of small pebbles and sand particles. An important distinction is drawn between sand deposition, which can occur at or below the bed surface, and pebble and cobble deposition, which is merely a surface phenomenon.     

Computational study of self‐centering buckling‐restrained braced frame seismic performance

Recent research developed and experimentally validated a self‐centering buckling‐restrained brace (SC‐BRB) that employs a restoring mechanism created using concentric tubes held flush with pretensioned shape memory alloy rods, in conjunction with a buckling‐restrained brace (BRB) that dissipates seismic energy. The present computational study investigated how the SC‐BRB can be implemented in real buildings to improve seismic performance. First, a computational brace model was developed and calibrated against experimental data, including the definition of a new cyclic material model for superelastic NiTi shape memory alloy. A parametric study were then conducted to explore the design space for SC‐BRBs. Finally, a set of prototype buildings was designed and computationally subjected to a suite of ground motions. The effect of the lateral resistance of gravity framing on self‐centering was also examined. From the component study, the SC‐BRB was found to dissipate sufficient energy even with large self‐centering ratios (as large as 4) based on criteria found in the literature for limiting peak drifts. From the prototype building study, a SC‐BRB self‐centering ratio of 0.5 was capable of reliably limiting residual drifts to negligible values, which is consistent with a dynamic form of self‐centering discussed in the literature. Because large self‐centering ratios can create significant overstrength, the most efficient SC‐BRB frame designs had a self‐centering ratio in the range of 0.5–1.5. Ambient building resistance (e.g., gravity framing) was found to reduce peak drifts, but had a negligible effect on residual drifts. Copyright © 2014 John Wiley & Sons, Ltd.     

结合MST划分和RHMRF-FCM算法的高分辨率遥感图像分割

针对基于像素的HMRF-FCM算法抗噪性差以及对地物复杂边界分割精度低的问题,提出一种结合形状信息的静态MST区域划分和RHMRF-FCM算法的高分辨率遥感图像分割方法。该方法定义一种静态MST同质区域划分准则,借助MST能较好表达边界和形状信息、能较好抑制几何噪声的特点,解决地物复杂边界的表达和降低分割结果中几何噪声问题。首先,利用MST静态划分将图像域划分成若干个均质区域,假设每个均质区域内光谱测度服从独立同一的多元高斯分布。然后,在此基础上构建了区域隐马尔可夫随机场模型,以及建立基于信息熵和KL信息正则化项的模糊聚类目标函数。最后,采用偏微分方法对分割模型参数进行求解,从而得到全局最优分割结果。为验证本文方法,对WorldView-3高分遥感图像进行分割试验。定性、定量分析了尺度参数、光谱相似性参数和区域紧致度参数对最优分割结果的影响,并对比分析本文算法和eCognition软件中的多分辨率分割算法、分水岭算法。     

浅述深水水道的形态学特征

目前深水水道的分类方案较多,本文基于深水水道的形态学特征,且聚焦于单一型深水水道,将其划分为顺直型(曲率介于1～1.25)、低弯度S型(曲率介于1.25～1.5)和高弯度S型(曲率>1.5)。其中,顺直型水道侵蚀作用最强,往往不发育天然堤沉积,无侧向加积;低弯度S型水道发育天然堤,并具有侧向加积;高弯度S型天然堤及侧向加积最为发育,决口扇常与之伴生。深水水道的曲率是水道形态的直观表现,曲率大小主要受深水地貌即深水地形坡度的影响。在上陆坡区域,地形坡度较大,沉积物能量强,深水水道以顺直型为主。中陆坡区域,随着地形坡度的减缓,水道的弯曲形态也逐渐增加,形成低弯度S型,直至下陆坡,水道演变为高弯度的S型。     

多裂纹扩展的扩展有限元法分析

建立了求解多裂纹扩展的扩展有限元法。引入裂纹交叉汇合加强函数以分析多裂纹交叉汇合过程;在裂纹附近区域使用广义形函数,并引入线增函数消除混合单元,可有效地提高裂纹附近的精度;用砂浆法（线段-线段接触法）结合增广型Lagrange乘子法处理裂纹段的接触条件,可以精确地模拟裂纹面约束,并方便地求解控制方程。算例分析了两方面内容：（1）计算交叉裂纹体的应力强度因子,结果表明提出的方法精度高;（2）模拟多裂纹扩展及交叉汇合过程,模拟的裂纹扩展路径与试验结果吻合得较好,表明了方法的可靠性。     

Shell‐shape and morphometric variability in Mytilus galloprovincialis from micro‐tidal environments: responses to different hydrodynamic drivers

Tidal conditions differently influence inter‐tidal organisms in terms of general physiological and metabolic responses. In this study we investigated the morphological response in shells of Mytilus galloprovincialis native to different micro‐tidal coastal environments in the Northern Adriatic Sea. Our purpose was to highlight the ecophenotypic variability across tidal levels and to elucidate how tidal currents and waves produced by anthropogenic activities may play a part in modulating shell morphology. Three sampling sites were selected: an open‐sea area 15 km off‐shore and two sites within the lagoon of Venice, the first near one of its three inlets, and the other one in the proximity of Venice city centre. At each sampling site, organisms were seasonally collected at different depths within their vertical zonation, either in the inter‐tidal zone – i.e. at both the highest and lowest tide zonation limits, and subtidally. The mussel shells were analysed by investigation of their morphometric relationships (height/length and width/length ratios) and by elliptic Fourier analysis of the shell contours. Shell thickness and condition index were also evaluated for a better comprehension of energy allocation/partitioning. Estimates based on long‐term measurements, visual observation, wind statistics and wave growth laws allowed an evaluation of the forces acting on shells. At the open‐sea site, the observed phenotypic variability of both shell shape and thickness was clearly related to the tidal vertical zonation. At the two lagoon sites, the currents generated by tidal flow through the inlet and the waves caused by the frequent passage of boats influenced both shell shape and thickness. A trade‐off between protection and growth was apparent along the tide gradient, as emphasized by the differences in the partitioning and allocation of energy between shell and flesh production.     

杨桃果脯的护色保形工艺研究

研究了杨桃果片在不同护色液中、不同护色条件下的护色效果 ,及其在不同保脆保形液中的保脆保形效果。结果表明 ,1.7mol LNaCl水溶液腌制、护色 ,0 .0 90mol LCaCl2 + 0 .34mol LNaCl水溶液保脆保形效果较好。