排序方式： 共有67条查询结果，搜索用时 390 毫秒
31.
N. Khare A. Mazumder P. Govil V. P. Singh 《Journal of the Geological Society of India》2009,73(3):379-385
Morphological variations with respect to the number of chambers in Neogloboquadrina pachyderma (Ehrenberg) were investigated in 25 surficial sediments of Indian Ocean taken along the N-S transect between 9.69° N and
55.01° S latitude and 80° E and 40° E longitude. The number of chamber was counted for at least 40 specimens picked for each
sample. The average number of chamber was correlated with the average temperature and salinity along the changing latitude.
The results showed a high correlation between the number of chambers and temperature and salinity. It was noted that number
of chambers decreases from equatorial to polar region. The carbonate saturation and nutrient availability could possibly be
other causes for the change in number of chambers. The results of this study, if applied on the subsurface marine sediments,
will bear implications on paleoclimatic condition in the Indian Ocean region. 相似文献
32.
Debasis Deb Akshay Kumar Rajat Pal Singh Rosha 《Geotechnical and Geological Engineering》2006,24(4):1021-1037
Leg pressure data from all shields of a longwall face are monitored and recorded in the surface computer. An algorithm is
developed to detect peak pressures or periodic roof weightings from these pressure data. The intensities and locations of
periodic roof weighting are further analyzed using artificial neural network for forecasting of forthcoming shield pressures.
The network was trained using data 153 m (500 ft) of face advance. Shield pressures are forecasted for the successive nine
mining cycles or approximately 9 m of face advancement. The results obtained validate the efficacy of the developed model. 相似文献
33.
S. Mazumder P. van Hemert A. Busch K-H.A.A. Wolf P. Tejera-Cuesta 《International Journal of Coal Geology》2006,67(4):267-279
Presently many research projects focus on the reduction of anthropogenic CO2 emissions. It is intended to apply underground storage techniques such as flue gas injection in unminable coal seams. In this context, an experimental study has been performed on the adsorption of pure CO2 and preferential sorption behavior of flue gas. A coal sample from the Silesian Basin in Poland (0.68% V Rr), measured in the dry and wet state at 353 K has been chosen for this approach. The flue gas used was a custom class industrial flue gas with 10.9% of CO2, 0.01% of CO, 9% of H2, 3.01% of CH4, 3.0% of O2, 0.106% of SO2 and nitrogen as balance.Adsorption isotherms of CO2 and flue gas were measured upto a maximum of 11 MPa using a volumetric method. Total excess sorption capacities for CO2 on dry and wet Silesia coal ranged between 1.9 and 1.3 mmol/g, respectively. Flue gas sorption capacities on dry and wet Silesia coal were much lower and ranged between 0.45 and 0.2 mmol/g, respectively, at pressures of 8 MPa. The low sorption capacity of wet coal has resulted from water occupying some of the more active adsorption sites and hence reducing the heterogeneity of adsorption sites relative to that of dry coal. Desorption tests with flue gas were conducted to study the degree of preferential sorption of the individual components. These experiments indicate that CO2 is by far the prefered sorbing component under both wet and dry conditions. This is followed by CH4. N2 adsorbs very little on the coal in the presence of CO2 and CH4. It is also observed that the adsorption of CO2 onto coal is not significantly hindered by the addition of other gases, other than dilution effect of the pressure.In addition to the sorption experiments, the density of the flue gas mixture has been determined up to 18 MPa at 318 K. A very good precision of these measurements were documented by volumetric methods. 相似文献
34.
Biplob Das Anita Narwani Blake Matthews Rick Nordin Asit Mazumder 《Journal of Paleolimnology》2009,42(2):167-181
We investigated how the history of local disturbances in a watershed can influence the regional coherence of ecosystem properties
in lakes that have similar morphometry and climatic conditions. We measured sedimentary δ13C, δ15N, C:N and %BSiO2 in Sooke Lake Reservoir (SOL) and Shawnigan Lake (SHL), which are located within 4 km of each other on Vancouver Island,
Canada. SOL is an impounded lake whose watershed has been fully protected over the last century, although the lake level has
been raised 3 times via impoundment during this period. SHL has a similar limnological regime, but the surrounding watershed
has been developed extensively for residential uses. We investigated how a pulse disturbance regime in SOL (i.e. repeated
dam raising) and a press disturbance regime in SHL (i.e. persistent development) influenced the variability of paleoindicators
in each system over time. We found that these contrasting disturbance regimes reduced the regional temporal coherence of aquatic
productivity between the two lakes (indicated by %BSiO2), but did not influence the regional coherence of nutrient status or the main carbon sources of the lakes (indicated by %C,
%N and δ13C). In contrast, an indicator of the sources and cycling of nitrogen (δ15N) showed increased coherence. Local disturbances also affected the variability of the paleoindicators within each system
over time. In SOL, impoundments led to both declines (%N, δ15N) and increases (δ13C) in the variability of paleoindicators. In SHL, persistent watershed development led to lower variability of two paleoindicators
(%N, %BSiO2). Overall, our data suggest that local disturbances can influence the %BSiO2 and C:N ratio of lake sediments, but are less likely to alter the regional coherence of %C, %N and δ13C between lakes.
Biplob Das and Anita Narwani contributed equally to this work. 相似文献
35.
Experiments are conducted in a laboratory flume on the propagation of a surface wave against unidirectional flow with a sediment bed. This article presents the spatial variation of bedforms induced by the wave-blocking phenomenon by a suitably tuned uniform fluid flow and a counter-propagating wave. The occurrence of wave-blocking is confirmed by finding a critical wave frequency in a particular flow discharge in which the waves are effectively blocked and is established using the linear dispersion relation. The purpose of this work is to identify wave-blocking and its influence on the development of bedforms over the sediment bed. Interestingly bedform signatures are observed at a transition of bedforms in three zones, with asymmetric ripples having a steeper slope downstream face induced by the incoming current, followed by flat sand bars beneath the wave-blocking zone and more symmetric ripples below the wave-dominated region at the downstream. This phenomenon suggests that the sediment bed is segmented into three different regions of bed geometry along the flow. The deviations of mean flows, Reynolds stresses, turbulent kinetic energy, and power spectral density due to the wave-blocking phenomenon are presented along the non-uniform flow over sediment bed. The bottom shear stress, bed roughness and stochastic nature of the bedform features are also discussed. The results are of relevance to engineers and geoscientists concerned with contemporary process as well as those interested in the interpretation of palaeoenvironmental conditions from fossil bedforms. © 2019 John Wiley & Sons, Ltd. 相似文献
36.
The effect of the geomagnetic Lorentz force on the muon component of extensive air shower (EAS) has been studied in a Monte Carlo generated simulated data sample. This geomagnetic field affects the paths of muons in an EAS, causing a local contrast or polar asymmetry in the abundance of positive and negative muons about the shower axis. The asymmetry can be approximately expressed as a function of transverse separation between the positive and negative muons barycentric positions in the EAS through opposite quadrants across the shower core in the shower front plane. In the present study, it is found that the transverse muon barycenter separation and its maximum value obtained from the polar variation of the parameter are higher for iron primaries than protons for highly inclined showers. Hence, in principle, these parameters can be exploited to the measurement of primary cosmic-ray mass composition. Possibility of practical realization of the proposed method in a real experiment is briefly discussed. 相似文献
37.
38.
39.
40.
Aerodynamic Properties of Rough Surfaces with High Aspect-Ratio Roughness Elements: Effect of Aspect Ratio and Arrangements 总被引：1，自引：1，他引：0
Jasim Sadique Xiang I. A. Yang Charles Meneveau Rajat Mittal 《Boundary-Layer Meteorology》2017,162(2):203-205
We examine the effect of varying roughness-element aspect ratio on the mean velocity distributions of turbulent flow over arrays of rectangular-prism-shaped elements. Large-eddy simulations (LES) in conjunction with a sharp-interface immersed boundary method are used to simulate spatially-growing turbulent boundary layers over these rough surfaces. Arrays of aligned and staggered rectangular roughness elements with aspect ratio >1 are considered. First the temporally- and spatially-averaged velocity profiles are used to illustrate the aspect-ratio effects. For aligned prisms, the roughness length (\(z_\mathrm{o}\)) and the friction velocity (\(u_*\)) increase initially with an increase in the roughness-element aspect ratio, until the values reach a plateau at a particular aspect ratio. The exact value of this aspect ratio depends on the coverage density. Further increase in the aspect ratio changes neither \(z_\mathrm{o}\), \(u_*\) nor the bulk flow above the roughness elements. For the staggered cases, \(z_\mathrm{o}\) and \(u_*\) continue to increase for the surface coverage density and the aspect ratios investigated. To model the flow response to variations in roughness aspect ratio, we turn to a previously developed phenomenological volumetric sheltering model (Yang et al., in J Fluid Mech 789:127–165, 2016), which was intended for low to moderate aspect-ratio roughness elements. Here, we extend this model to account for high aspect-ratio roughness elements. We find that for aligned cases, the model predicts strong mutual sheltering among the roughness elements, while the effect is much weaker for staggered cases. The model-predicted \(z_\mathrm{o}\) and \(u_*\) agree well with the LES results. Results show that the model, which takes explicit account of the mutual sheltering effects, provides a rapid and reliable prediction method of roughness effects in turbulent boundary-layer flows over arrays of rectangular-prism roughness elements. 相似文献