Experiment on visualizing micro-level surface characters of sediment sections: a methodological approach to reflectance-based alternative petrographic image analysis   总被引：1，自引：1，他引：0  

Sudip Dey  Chandrani Debbarma  Prasamita Sarkar  Muh Aris Marfai 《Arabian Journal of Geosciences》2011,4(5-6):899-906

This paper discusses an experiment on digital imaging and visualizing the surface condition of the sediment depositions. For that purpose, a part of South Tripura district was selected as sampling site. Physically, the selected area is located in a fold belt and preserves the history of Tertiary–Quaternary landform evolution in the main types of sediment depositions. Three samples, each from the different types of Tertiary depositions, were finally taken for thick section making, optical microscopy under reflected light, and soft computing. Geometric optical measurement and physical optical measurement were done to understand the surface condition of Bokabil, Tipam, and Duplitila samples by bidirectional reflectance distribution function and radiometric scales (within 0–255 digital number values). Maximum surface smoothness or near-perfect reflection surface was measured by brightness–contrast slicing operation.  相似文献   

Repetitiveness and underlying characteristics of climatologic parameters in winter     

Mira Paskota  Dragana Vujović  Nedeljko Todorović 《Theoretical and Applied Climatology》2013,113(1-2):317-328

Starting from the standpoint that there are seasonal differences of climate variations on both global and local level, the authors of this paper had focused on analyzing climatologic parameters in winter months. The trends of several important parameters were detected, with temperature and precipitation having increasing, but number of ice days and snow cover having decreasing trends. Spectral analysis showed repetitive nature of climatologic parameters, some of them having the same or similar periods of about 6 to 7 years, 10 to 12 or 17.5 years, and 22 to 24 years. The precipitation has periodicity of 8 and 14 years. Further analysis of the underlying structure of the data by principal component analysis detected three easily explained dimensions: Temperature-Snow, Precipitation-Cyclone and Spring-in-Winter dimension. The spectral analysis of three virtual variables obtained by principal component analysis confirmed good agreement of original variables with the virtual dimensions.  相似文献   

HST Imaging of an Old Galaxy Group at Z=1.55     

Andrew J. Bunker  Hyron Spinrad  Ross McLure  Arjun Dey  James Dunlop  John Peacock  Daniel Stern  Rodger Thompson  Ian Waddington  Rogier Windhorst 《Astrophysics and Space Science》2002,281(1-2):527-528

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Old elliptical galaxies at  z ≃ 1.5  and the Kormendy relation     

I. Waddington  R. A. Windhorst  S. H. Cohen  J. S. Dunlop  J. A. Peacock  R. Jimenez  R. J. McLure  A. J. Bunker  H. Spinrad  A. Dey  D. Stern 《Monthly notices of the Royal Astronomical Society》2002,336(4):1342-1350

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Early Neoarchaean A-type granitic magmatism by crustal reworking in Singhbhum craton: Evidence from Pala Lahara area,Orissa     

Abhishek Topno  Sukanta Dey  Yongsheng Liu  Keqing Zong 《Journal of Earth System Science》2018,127(3):43

Several volumetrically minor \(\sim \)2.8 Ga anorogenic granites and rhyolites occur along the marginal part of the Singhbhum craton whose origin and role in crustal evolution are poorly constrained. This contribution presents petrographic, geochemical, zircon U–Pb and trace element, and mineral chemical data on such granites exposed in the Pala Lahara area to understand their petrogenesis and tectonic setting. The Pala Lahara granites are calc-alkaline, high-silica rocks and define a zircon U–Pb age of 2.79 Ga. These granites are ferroan, weakly metaluminous, depleted in Al, Ca and Mg and rich in LILE and HFSE. They are classified as A2-type granites with high Y/Nb ratios. Geochemical characteristics (high \(\hbox {SiO}_{2}\) and \(\hbox {K}_{2}\hbox {O}\), very low MgO, Mg#, Cr, Ni and V, negative Eu anomaly, flat HREE and low Sr/Y) and comparison with melts reported by published experimental studies suggest an origin through high-temperature, shallow crustal melting of tonalitic/granodioritic source similar to the \(\sim \)3.3 Ga Singhbhum Granite. Intrusion of the Pala Lahara granites was coeval with prominent mafic magmatism in the Singhbhum craton (e.g., the Dhanjori mafic volcanic rocks and NNE–SSW trending mafic dyke swarm). It is suggested that the \(\sim \)2.8 Ga A-type granites in the Singhbhum craton mark a significant crustal reworking event attendant to mantle-derived mafic magmatism in an extensional tectonic setting.  相似文献   

2D viscoplastic finite element modelling of slow landslides: the Portalet case study (Spain)   总被引：3，自引：1，他引：2  

J. A. Fernández-Merodo  J. C. García-Davalillo  G. Herrera  P. Mira  M. Pastor 《Landslides》2014,11(1):29-42

This paper proposes a hydro-geomechanical finite element model to reproduce the kinematic behaviour of large slow landslides. The interaction between solid skeleton and pore fluids is modelled with a time dependent u–p _w formulation and a groundwater model that takes into account recorded daily rainfall intensity. A viscoplastic constitutive model based on Perzyna’s theory is applied to reproduce soil viscous behaviour and the delayed creep deformation. The proposed model is applied to Portalet landslide (Central Spanish Pyrenees). This is an active paleo-landslide that has been reactivated by the construction of a parking area at the toe of the slope. The stability analysis reveals that, after the constructive solutions were undertaken, the slope is in a limit equilibrium situation. Nevertheless, time-dependent analysis reproduces the nearly constant strain rate (secondary creep) and the acceleration/deceleration of the moving mass due to hydrological changes. Overall, the model reproduces a 2-m displacement in the past 8  years that coincides with in situ monitoring data. The proposed model is useful for short- and mid-term predictions of secondary creep. However, long-time predictions remain uncertain, stability depends strongly on the position of the water table depth and new failures during tertiary creep due to soil temporal microstructural degradation are difficult to calibrate.  相似文献   

Seismic assessment in southern Baromura hill,northeast India,considering geophysical aspects     

Sudip Dey  Prasamita Sarkar  Chandrani Debbarma  Sushmita Paul 《Environmental Earth Sciences》2012,66(2):421-431

This paper aims to assess the geophysical signatures like morphology and structure of a fault line, which is situated in a part of southern Baromura hill of Tripura, northeast India. In this work manual observations and technical applications were adopted for understanding the morphological and structural characters of the fault line. As tectonic mapping is one of the main objectives of this study, the remote sensing technique was used to prepare a tectonic map of the study area. Geothermal range of the area was measured by unsupervised classification of Landsat TM thermal infrared band (band 6). The classified thermal band was overlaid by another classified shortwave infrared band (band 7 of Landsat TM), which explains the structural evidences of the study area. In addition, an automated digital elevation model (DEM) was prepared to assess the morphological characters of the study area particularly near the confluence of R. Maharani and R. Gumti. To analyse the structural condition of the faulted zone, resistivity characters of the rocks were measured by “vertical electrical sounding” (VES) method. The electrical resistivity character of this area strongly supports that a displacement occurred in this place. Finally an attempt was made to explain the character of faulting on the basis of morphological signatures and structural evidences for future disaster management planning.  相似文献   

Turbulence in mobile-bed streams   总被引：2，自引：1，他引：1  

Subhasish Dey  Ratul Das  Roberto Gaudio  Sujit K. Bose 《Acta Geophysica》2012,60(6):1547-1588

This study is devoted to quantify the near-bed turbulence parameters in mobile-bed flows with bed-load transport. A reduction in near-bed velocity fluctuations due to the decrease of flow velocity relative to particle velocity of the transporting particles results in an excessive near-bed damping in Reynolds shear stress (RSS) distributions. The bed particles are associated with the momentum provided from the flow to maintain their motion overcoming the bed resistance. It leads to a reduction in RSS magnitude over the entire flow depth. In the logarithmic law, the von Kármán coefficient decreases in presence of bed-load transport. The turbulent kinetic energy budget reveals that for the bed-load transport, the pressure energy diffusion rate near the bed changes sharply to a negative magnitude, implying a gain in turbulence production. According to the quadrant analysis, sweep events in mobile-bed flows are the principal mechanism of bed-load transport. The universal probability density functions for turbulence parameters given by Bose and Dey have been successfully applied in mobile-bed flows.  相似文献   

Scour Downstream of Grade Control Structures under the Influence of Upward Seepage     

Mahmood Shafai-Bejestan  Seyed Mojtaba Razavi Nabavi  Subhasish Dey 《Acta Geophysica》2016,64(3):694-710

The installation of free falling jet grade control structures has become a popular choice for river bed stabilization. However, the formation and development of scour downstream of the structure may lead to failure of the structure itself. The current approaches to scour depth prediction are generally based on studies conducted with the absence of upward seepage. In the present study, the effects of upward seepage on the scour depth were investigated. A total of 78 tests without and with the application of upward seepage were carried out using three different sediment sizes, three different tailwater depths, four different flow discharges, and four different upward seepage flow discharge rates. In some tests, the three-dimensional components of the flow velocity within the scour hole were measured for both the cases with and without upward seepage. The scour depth measured for the no-seepage results compared well with the most accurate relationship found in the literature. It was found that generally the upward seepage reduced the downward velocity components near the bed, which led to a decrease in the maximum scour depth. A maximum scour depth reduction of 49% was found for a minimum tailwater depth, small sediment size, and high flow discharge. A decay of the downward velocity vector within the jet impingement was found due to the upward seepage flow velocity. The well known equation of D’Agostino and Ferro was modified to account for the effect of upward seepage, which satisfactorily predicted the experimental scour depth, with a reasonable average error of 10.7%.  相似文献   

Occurrence,distribution and partitioning of nonionic surfactants and pharmaceuticals in the urbanized Long Island Sound Estuary (NY)     

Pablo A. Lara-Martín  Eduardo González-Mazo  Mira Petrovic  Damià Barceló  Bruce J. Brownawell 《Marine pollution bulletin》2014

This work deals with the environmental distribution of nonionic surfactants (nonylphenol and alcohol ethoxylates), their metabolites (NP, nonylphenol; NPEC, nonylphenol ethoxycarboxylates; and PEG, polyethylene glycols) and a selection of 64 pharmaceuticals in the Long Island Sound (LIS) Estuary which receives important sewage discharges from New York City (NYC). Most target compounds were efficiently removed (>95%) in one wastewater treatment plant monitored, with the exception of NPEC and some specific drugs (e.g., hydrochlorothiazide). Concentrations of surfactants (1.4–4.5 μg L⁻¹) and pharmaceuticals (0.1–0.3 μg L⁻¹) in seawater were influenced by tides and sampling depth, consistent with salinity differences. Surfactants levels in suspended solids samples were higher than 1 μg g⁻¹, whereas only most hydrophobic or positively charged pharmaceuticals could be found (e.g., tamoxifen, clarithromycin). Maximum levels of target compounds in LIS sediments (PEG at highest concentrations, 2.8 μg g⁻¹) were measured nearest NYC, sharply decreasing with distance from major sewage inputs.  相似文献