Wave breaking and bubble formation associate energy dissipation and wave setup     

Hoque  Ashabul  Hossain  Nur  Ali  Shuzon  Rahman  Masudar 《Ocean Dynamics》2019,69(8):913-923

Ocean Dynamics - In this work, theoretical development of void fraction effect over wave energy dissipation and wave setup in a surf zone is made. The formulation incorporates simple energy...  相似文献   

Stellar structure and mass loss on the upper asymptotic giant branch     

Noam Soker  Amos Harpaz 《Monthly notices of the Royal Astronomical Society》1999,310(4):1158-1164

We examine the envelope properties of asymptotic giant branch (AGB) stars as they evolve on the upper AGB and during the early post-AGB phase. Because of the high mass-loss rate, the envelope mass decreases by more than an order of magnitude. This makes the density profile below the photosphere much shallower, and the entropy profile much steeper. We discuss the possible role of these changes in the profiles in the onset of the high mass-loss rate (superwind) and the large deviation from spherical mass loss at the termination of the AGB. We concentrate on the idea that the shallower density profile and steeper entropy profile allow the formation of cool magnetic spots, above which dust forms much more easily.  相似文献   

Morphometry and distribution of isolated caves as a guide for phreatic and confined paleohydrological conditions   总被引：1，自引：0，他引：1  

Amos Frumkin  Itay Fischhendler 《Geomorphology》2005,67(3-4):457-471

Isolated caves are a special cave type common in most karst terrains, formed by prolonged slow water flow where aggressivity is locally boosted. The morphometry and distribution of isolated caves are used here to reconstruct the paleohydrology of a karstic mountain range. Within a homogenous karstic rock sequence, two main types of isolated caves are distinguished, and each is associated with a special hydrogeologic setting: maze caves form by rising water in the confined zone of the aquifer, under the Mt. Scopus Group (Israel) confinement, while chamber caves are formed in phreatic conditions, apparently by lateral flow mixing with a vadose input from above.  相似文献   

Influence of Zostera marina canopies on unidirectional flow,hydraulic roughness and sediment movement     

A. Lefebvre  C.E.L. ThompsonC.L. Amos 《Continental Shelf Research》2010

Seagrasses develop extensive or patchy underwater meadows in coastal areas around the world, forming complex, highly productive ecosystems. Seagrass canopies exert strong effects on water flow inside and around them, thereby affecting flow structure, sediment transport and benthic ecology. The influence of Zostera marina canopies on flow velocity, turbulence, hydraulic roughness and sediment movement was evaluated through laboratory experiments in 2 flumes and using live Z. marina and a mobile sand bed. Profiles of instantaneous velocities were measured and sediment movement was identified upstream, within and downstream of patches of different sizes and shoot density and at different free-stream velocities. Flow structure was characterised by time-averaged velocity, turbulence intensity and Turbulent Kinetic Energy (TKE). When velocity data were available above the canopy, they were fitted to the Law of the Wall and shear velocities and roughness lengths were calculated. When a seagrass canopy was present, three layers were distinguishable in the water column: (1) within canopy represented by low velocities and high turbulence; (2) transition zone around the height of the canopy, where velocities increased, turbulence decreased and TKE was high; and (3) above canopy where velocities were equal or higher than free-stream velocities and turbulence and TKE were lower than below. Shoot density and patch-width influenced this partitioning of the flow when the canopy was long enough (based on flume experiments, at least more than 1 m-long). The enhanced TKE observed at the canopy/water interface suggests that large-scale turbulence is generated at the canopy surface. These oscillations, likely to be related to the canopy undulations, are then broken down within the canopy and high-frequency turbulence takes place near the bed. This turbulence ‘cascade’ through the canopy may have an important impact on biogeochemical processes. The velocity above the canopy generally followed a logarithmic profile. Roughness lengths were higher above the canopy than over bare sand and increased with increasing distance from the leading edge of the canopy; however, they were still small (<1 cm) compared to other studies in the literature. Within and downstream of the canopy, sediment movement was observed at velocities below the threshold of motion. It was likely caused by the increased turbulence at those positions. This has large implications for sediment transport in coastal zones where seagrass beds develop.  相似文献   

The erosion rates of cohesive sediments in Venice lagoon,Italy     

Carl L. Amos  G. Umgiesser  C. Ferrarin  C.E.L. Thompson  R.J.S. Whitehouse  T.F. Sutherland  A. Bergamasco 《Continental Shelf Research》2010

The stability of cohesive sediments from Venice lagoon has been measured in situ using the benthic flume Sea Carousel. Twenty four stations were occupied during summertime, and a sub-set of 13 stations was re-occupied during the following winter. Erosion thresholds and first-order erosion rates were estimated and showed a distinct difference between inter-tidal and sub-tidal stations. The higher values for inter-tidal stations are the result of exposure that influences consolidation, density, and organic adhesion. The thresholds for each state of sediment motion are well established. However, the rate of erosion once the erosion threshold has been exceeded has been poorly treated. This is because normally a time-series of sediment concentration (C) and bed shear stress (τ₀(t)) is used to define threshold stress or cohesion (τ_crit,z) and erosion rate (E). Whilst solution of the onset of erosion, τ_crit,0, is often reported, the evaluation of the erosion threshold variation through the process of erosion (eroded depth) is usually omitted or not estimated. This usually leads to assumptions on the strength profile of the bed which invariably has no credibility within the topmost mm of the bed where most erosion takes place. It is possible to extract this information from a time-series through the addition of a step in data processing. This paper describes how this is done, and the impact of this on the accuracy of estimates of the excess stress (τ₀(t)–τ_crit,z) on E.  相似文献   

Characterization of phosphoric acid- and lime-stabilized tropical lateritic clay   总被引：4，自引：2，他引：2  

Amin Eisazadeh  Khairul Anuar Kassim  Hadi Nur 《Environmental Earth Sciences》2011,63(5):1057-1066

The effect of calcium-based stabilizers such as lime on the geotechnical properties of tropical soils has been reported by many researchers. However, the amount of literature available on the micro-structural, molecular, and leaching characteristics of lime and in particular phosphoric acid-stabilized lateritic clays has been limited. This research was carried out in an attempt to identify the time-dependent soil-chemical reactions. In addition, the possible mechanisms that contributed to the stabilization process were discussed in the light of various spectroscopic and microscopic techniques such as X-ray diffractometry (XRD), energy-dispersive X-ray spectrometry (EDAX), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), and nuclear magnetic resonance spectroscopy (NMR) etc. Based on the results it was found that in lime-treated samples, the coating action of free iron oxides on clay particles imposed inhibitive effects on the dissolution of clay alumina. On the other hand, in phosphoric acid-stabilized soil, due to the increase in solubility of metal oxides and also the subsequent release of clay alumina the formation of cementitious compounds were more feasible. From engineering point of view, the phosphoric acid-stabilized lateritic soil showed the highest degree of improvement with an approximately threefold strength increase in comparison with the natural soil over an 8-month curing period.  相似文献   

Identifying spatial heterogeneity of coal resource quality in a multilayer coal deposit by multivariate geostatistics     

Mohamad Nur Heriawan  Katsuaki Koike   《International Journal of Coal Geology》2008,73(3-4):307-330

This study presents a new geostatistical approach to characterization of the geometry and quality of a multilayer coal deposit using the data of seam thickness as a geometric property and the contents of ash, sodium, total sulphur, and the heating value as quality properties. A coal deposit in East Kalimantan (Borneo), Indonesia, which has a synclinal geological structure, was chosen as the study site. Semivariogram analysis clarified the strong dependence of heating value on ash content in the top and bottom parts of each seam and the existence of a strong correlation with sodium content over the sub-seams in the same location. The correlations between the geometry and quality of the seams were generally weak. A linear coregionalization model was used to derive the spatial correlation coefficients of two variables at each scale component from the single- and cross-semivariogram matrices. Because the data were correlated spatially in the same seam or over different seams, multivariate techniques (ordinary cokriging and factorial cokriging) were mainly used and the resultant spatial estimates were compared to those derived using a univariate technique (ordinary kriging). A factorial cokriging was effective to decompose the spatial correlation structures with different scales. Another important characteristic was that the sodium content shows distinct segregation: the low zones are concentrated near the boundary of the sedimentary basin, while the high zones are concentrated in the central part. The main component of sodium originates from the abundance of saline water. Therefore, it can be inferred that seawater had stronger effects on the coal depositional process in the central basin than in the border part. The geostatistical modeling results suggest that the thicknesses of all the major seams were controlled by the syncline structure, while the coal qualities chiefly were originated from the coal depositional and diagenetic processes.  相似文献   

Using time-lapse 4D seismic to monitor saturation changes in carbonate reservoirs     

Mohamed Saleh Efnik  Samsuddin H. Taib  Nur Islami 《Journal of the Geological Society of India》2016,88(6):736-742

In the past ten years, time-lapse (4D) seismic has evolved as a standard way of monitoring reservoir performance. The method is now being used as good reservoir management practice to provide evidence of saturation changes within the reservoir at field scale. 4D provides a new piece of data describing the dynamic behavior of the reservoir fluids between the wells, often limited to small scale monitoring at the borehole scale. Thus, it provides sophisticated techniques for reservoir monitoring and management relying on the integration of geological models, static and dynamic properties of the reservoir rock, and detailed production and pressure field data.While 4D seismic data has been very successful in monitoring hydrocarbon production from clastic reservoirs, this work has focused on implementing 4D time lapse to monitor saturation changes in carbonate reservoirs and it’s capability to be used as enhanced oil recovery (EOR) tool that can help in enhancing the recovery factor for the filed and help to locate new drilling to sweep more oil out of the reservoir and locate the by-pass oil.The principal goal of this research was to detect the maximum change in seismic attributes (amplitude, acoustic impedance, travel time) that could occur as a result of oil production, water and gas injection in carbonate reservoirs by using time-lapse 4D seismic.  相似文献   

Hybrid off-river augmentation system as an alternative raw water resource: the hydrogeochemistry of abandoned mining ponds     

Faradiella Mohd Kusin  Mohd Syakirin Md Zahar  Siti Nurjaliah Muhammad  Nur Diyana Mohamad  Zafira Md Zin  Sharifah Mohd Sharif 《Environmental Earth Sciences》2016,75(3):230

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Multivariate statistical analysis for identifying water quality and hydrogeochemical evolution of shallow groundwater in Quaternary deposits in the Lower Kelantan River Basin,Malaysian Peninsula     

Nur Hayati Hussin  Ismail Yusoff  Wan Zakaria Wan Muhd Tahir  Ibrahim Mohamed  Adriana Irawati Nur Ibrahim  Adzhar Rambli 《Environmental Earth Sciences》2016,75(14):1081

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