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811.
Numerical modelling of alternate bar formation,development and sediment sorting in straight channels
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A two‐dimensional shallow water hydro‐sediment‐morphodynamic model is applied to investigate alternate bar formation, development and sediment sorting in straight channels. The model is coupled, explicitly incorporating the flow–sediment–bed interactions by using the full mass and momentum conservation equations, which are numerically solved by a well‐balanced version of the finite volume Slope Limiter Centred (SLIC) scheme. The model is first tested against a flume experiment on alternate bars formed over a uniform sediment bed, which clearly exhibits processes of bar formation, migrating and finally approaching an equilibrium state. Then it is applied to another flume experiment on alternate bars due to non‐uniform sediment transport. The computational results are evaluated, with a focus on the longitudinal and vertical sediment sorting. It is argued for the first time that the inconsistent sediment sorting patterns observed in previous studies are determined by different sediment transport conditions, i.e. full versus partial transport. When a condition of full transport is achieved, under which all size fractions are fully mobilized and transported, the longitudinal surface sediment shows a sorting pattern of coarse‐on‐head and fine‐in‐pool, and the vertical substrate sediment exhibits an immobile‐fine‐coarse structure upwards. In contrast, for a partial transport condition, under which only finer fraction participates in the transport process, an opposite longitudinal pattern (i.e. fine‐on‐head and coarse‐in‐pool) and a different vertical structure (i.e. immobile‐coarse‐fine) are observed. Concurrently, numerical experiments with specified conditions show that the critical aspect ratio for the formation of migrating alternate bars is approximately equal to 12. With the increase of the aspect ratio, the bar length grows gradually, while the bar height increases rapidly for moderate values of the aspect ratio and then keeps nearly stable. The bar celerity, however, is weakly sensitive to the variation of this ratio. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
812.
The links between entrance geometry,hypsometry and hydrodynamics in shallow tidally dominated basins
Peter J. de Ruiter Julia C. Mullarney Karin R. Bryan Christian Winter 《地球表面变化过程与地形》2019,44(10):1957-1972
Geomorphological characteristics of tidal basins control hydrodynamics and sediment transport potential within such basins, for example, by adjusting the balance in tidal asymmetry. In this study we examine the effects of entrance geometry on tidal velocity asymmetry, slack water asymmetry, bed shear stress patterns and hypsometric profile shapes by comparison of six shallow meso-tidal basins of Tauranga Harbour, New Zealand. Numerical model results show how tidal distortion increases with distance from a basin entrance. A simple ratio between basin width and entrance width defines levels of basin dilation. Sub-basins with a constricted geometry and deep entrance channels are associated with small bed shear stress values and high rates of flood-directed tidal velocity asymmetry in the sheltered basin centres, indicating a large potential for sediment deposition of larger particles. Moreover, slack water asymmetry within these basins is weakly ebb-directed, indicating a small potential for transport of fine sediments out of the basins. The constricted depositional basins are characterized by convex hypsometric profiles with elevated intertidal regions. Unconstricted geometries are associated with larger bed shear stress values and more ebb-directed tidal velocity asymmetry within basin centres, suggesting limited potential for overall sediment deposition. The slack tide duration asymmetry is weakly flood-dominant indicating that limited input of fine sediment into the basins is possible. The comparatively high-energy conditions within these exposed basins are associated with a less convex hypsometric intertidal profile. The ability to estimate tidal asymmetries is advantageous when developing management strategies related to ecosystem functioning, navigability or coastal protection in specific geomorphic settings. © 2019 John Wiley & Sons, Ltd. 相似文献
813.
To clarify the confusion surrounding species identification and state intraspecific variations, this research studied the morphological taxonomy of five species, Kentrophyllum cf. setigerum Petz et al., 1995; Zosterodasys shumerica Aliev, 1990; Frontonia tchibisovae Burkovsky, 1970; Neourostylopsis orientalis Chen et al., 2013; and Apoholosticha cf. sinica Fan et al., 2014, which were collected from Chongming Island's marsh wetlands. Kentrophyllum cf. setigerum possesses less somatic kineties than K. setigerum(19–26 right and 18–25 left kineties vs 35–40 right and 30 left kineties). Whether Z. shumerica is identical to Z. transversa Foissner et al., 1994, which was presented in a previous report, was negated. The improved diagnosis for the species is provided. Frontonia tchibisovae was confirmed to have three or four micronuclei, and the number of kinetosome rows in its peniculus 3 varied between China and Russia populations. The new population of N. orientalis bears cortical granules, which differs from the original population that has an arrangement of rows across the dorsal bristles. For A. cf. sinica, there are colorless cortical granules on the ventral side of the new population, whereas in the previously reported populations bright orange, spherical granules were clustered around dorsal cilia. Additionally, we sequenced the small-subunit(SSU) rRNA genes of K. cf. setigerum, N. orientalis, and A. cf. Sinica, and compared the new and reported populations. For the first time, we also provide a species list, including 33 ciliates collected from the wetlands based on living observation and silver staining. 相似文献
814.
传统聚落空间形态是聚落地域性景观与文脉价值的集中载体,对其形态的保护与延续是乡村聚落规划设计的重要原则与策略。其中,山地传统聚落因所处地形复杂而具有区别于平原聚落的突出的竖向形态特征,但当前研究普遍缺少针对聚落三维形态的综合量化方法。本文在已有的聚落二维平面空间形态研究基础上,创新性引入竖向空间和建筑混乱度两方面指标,构建山地传统聚落三维形态量化指标体系,以黔东南苗族山地传统聚落为例,运用因子分析和聚类分析方法研究苗族聚落形态特征与类型。主要结论如下:(1)因子聚类将聚落形态指标综合提取为三维空间因子、规模形态因子、空间结构因子三大主要因子;(2)聚类分析实现了对所涉及苗族聚落形态的有效划分;(3)在此基础上,本文结合自然环境等其他质性因素,将苗族聚落形态划分为深谷山腰型松散指状聚落、缓坡型松散团带状聚落、平坡型致密团状聚落、复合地形松散指状聚落4种典型类型,并进一步解释了不同类型聚落形态的异同与生成逻辑,实现了对苗族聚落三维形态的科学表征与分类。这一方法科学有效地揭示了山地聚落形态的三维本质特征,对未来聚落形态规划与分类保护提供了有益的量化导引。 相似文献
815.
黄土地貌是按独特的演化模式形成当今复杂多样且有序分异的地貌形态组合。基于数学形态法将合水县地区黄土地貌分类并计算得出塬梁峁地貌单元的分类指标,再通过黄土地貌单元的形态特征及分类指标,对黄土塬梁峁地貌演化模式作出定量化和可视化表达,并预测塬即将消失的区域。研究发现:① 似圆度是界定黄土地貌单元演化进程的重要指标,黄土地貌单元在演化过程中,其形状规律程度逐渐增加;可用周长面积比和平均坡度界定塬梁的分界,可用边界临接指数界定梁峁的分界。② 塬向梁演化实质就是残塬向树杈梁演化。残塬是人类赖以生存的地貌单元,是固沟保塬工程的重点实施对象。 相似文献
816.
为初步评估海洋资源用作混凝土原材料的可行性,先通过数字图像技术求取海砂与河砂颗粒样本的椭圆率、圆度及坚固性参数,对两者颗粒形态特征做出综合评价,然后采用RCT法检测海拌混凝土游离氯离子含量,并测定混凝土不同龄期的抗压强度及碳化深度。结果表明,海砂与河砂颗粒细长程度、棱角及内凹曲面显著程度均非常接近,颗粒形态不存在本质差异;天然海水有助于混凝土早期强度的提升,对后期强度及碳化深度的影响则较为微弱;商品海砂会对混凝土力学性能产生轻微负面影响,并使抗碳化性能大幅下降。 相似文献
817.
库里亚藻(Coolia)是一类广泛分布且具有生物毒性的海洋底栖甲藻。本研究对近年来在中国南海西沙群岛海域采集分离的4株库里亚藻, 通过光镜及电镜下的形态学观察, 并结合基于核糖体大亚基(large subunit, LSU)rDNA(D1-D3)和内部转录间隔区(internal transcribed spacer, ITS)的序列进行系统发育分析, 鉴定该4个株系为热带库里亚藻(Coolia tropicalis)。在卤虫(Artemia salina)生物毒性试验中, 热带库里亚藻不同株系毒素提取液对卤虫幼虫表现出了毒性差异, XS554株系的48h半致死浓度(LC50)为1.42mg·mL -1(约相当于1.1×10 5cells·mL -1), 5XS15株系的LC50为1.92mg·mL -1(约相当于1×10 5cells·mL -1)。 相似文献
818.
南海神狐天然气水合物系统沉积物中自生黄铁矿的特征研究 总被引:1,自引:0,他引:1
南海神狐海域是中国最重要的天然气水合物调查研究区之一,为了解水合物存在对沉积物地球化学环境的影响,对采自神狐海域W19B井位的沉积物样品进行了矿物学和地球化学研究。X射线衍射分析和主量元素结果显示部分层位有异常高含量的硫化物(主要为黄铁矿)。扫描电镜结果表明随着样品深度的增加,黄铁矿的晶面、晶棱更加明显,且集合体形态呈现聚莓→单莓→细粒的变化趋势,扫描电镜还观察到草莓状黄铁矿向细粒自形黄铁矿转化的中间产物。在53.0 mbsf(meters below seafloor)和140.4 mbsf层位均发现异常高含量的黄铁矿。其中140.4 mbsf层位黄铁矿充填有孔虫壳体的现象普遍,并伴有大量柱状黄铁矿产出,可能与有机质和甲烷厌氧氧化相关,但主导作用应为甲烷厌氧氧化,该层位可能位于古硫酸根-甲烷界面(sulfate-methane interface,SMI)附近。根据所得结果,推测地质历史时期中甲烷异常渗漏事件的发生,致使向上的甲烷通量增加,推动SMI上移,导致53.0 mbsf和140.4 mbsf界面处因甲烷厌氧氧化而形成大量黄铁矿。多个黄铁矿富集层的存在可能表示沉积史中曾发生多期次的深部流体渗漏或者天然气水合物的分解活动。 相似文献
819.
One strain of unicellular greenish algae embedded by mucilage was successfully isolated from equatorial area in the Indian Ocean. Microscopic observation, ultrastructure features and genetic identification confirmed that the strain was closely related to Cyanothece sp., which was a cyanobacteria species with great ecological significance.Cells were solitary with oval or bacilliform shapes. Diameters of this strain were relatively small, ranging from 2.5 to 6.5 μm on average. Ultrastructure of cells was simple. Thylakoids were arranged parietal and keritomized content were observed in the thylakoid region. Various electron-transparent granules with low electron-dense region as well as cyanophycin or glycogen granules-like organelle and carbonxysomes were also observed. For pigment composition, the dominant pigments were chlorophyll a, β-Carotene, Zeaxanthin and an unknown pigment, contributing 23.8%, 26.1%, 14.7% and 15.7% to total pigments respectively. The phylogenetic analysis of16 S rRNA gene and nif H gene confirmed that Strain EIO409 was closely related with Cyanothece sp.. 相似文献
820.
为了澄清中国沿海尖刺拟菱形藻Pseudo-nitzschia pungens Hasle的种下分类学现状, 从我国沿海分离并建立了32个尖刺拟菱形藻的单克隆培养株系, 结合光学显微镜下的群体特征和透射电镜下的超微形态学特征, 以及基于核糖体转录间隔区(ITS)的分子系统学数据, 鉴定得到尖刺拟菱形藻的两个变种: 尖刺拟菱形藻原变种P. pungens var. pungens和尖刺拟菱形藻阿维罗变种P. pungens var. averiensis。文章对其形态学特征进行了详细描述, 并利用高效液相色谱-质谱联用法(LC-MS/MS)对培养株系的多莫酸(DA)进行了检测, 但未检测到DA。 相似文献