Seasonal variation of pteropods from the Western Arabian Sea sediment trap     

R. Mohan  K. Verma  L. P. Mergulhao  D. K. Sinha  S. Shanvas  M. V. S. Guptha 《Geo-Marine Letters》2006,26(5):265-273

Sediment trap samples collected from the Western Arabian Sea yielded a rich assemblage of intact and non-living (opaque white) pteropod tests from a water depth of 919 m during January to September 1993. Nine species of pteropods were recorded, all (except one) displaying distinct seasonality in abundance, suggesting their response to changing hydrographical conditions influenced by the summer/winter monsoon cycle. Pteropod fluxes increased during the April–May peak of the intermonsoon, and reached maximum levels in the late phase of the southwest summer monsoon, probably due to the shallowing of the mixed layer depth. This shallowing, coupled with enhanced nutrient availability, provides ideal conditions for pteropod growth, also reflected in corresponding fluctuations in the flux of the foraminifer Globigerina bulloides. Pteropod/planktic foraminifer ratios displayed marked seasonal variations, the values increasing during the warmer months of April and May when planktic foraminiferal fluxes declined. The variation in fluxes of calcium carbonate, organic carbon and biogenic opal show positive correlations with fluxes of pteropods and planktic foraminifers. Calcium carbonate was the main contributor to the total particulate flux, especially during the SW monsoon. In the study area, pteropod flux variations are similar to the other flux patterns, indicating that they, too could be used as a potential tool for palaeoclimatic reconstruction of the recent past.  相似文献   

Statistical evaluation of methods for the calculation of static formation temperatures in geothermal and oil wells using an extension of the error propagation theory     

Surendra P. Verma  J. Andaverde  E. Santoyo   《Journal of Geochemical Exploration》2006,89(1-3):398

The feasibility of using the more sophisticated weighted least-squares (WLS) model, as opposed to the traditional ordinary least-squares (OLS), in linear regressions of BHT data to estimate the static formation temperatures (SFT) was investigated. The most commonly used analytical methods (line-source; spherical and radial heat flow; and cylindrical heat source) were applied. Error propagation equations were derived to calculate errors in the time function of each method. These errors were combined with the BHT measurement errors to compute weighting factors for applying the WLS. Intercept uncertainties were estimated for all regressions using sets of synthetic and actual borehole logs taken from geothermal and oil applications. SFT computed with the spherical and radial heat flow method were generally greater than those from the other two methods.  相似文献   

Evidence of reworking and resuspension of carbonates during last glacial maximum and early deglacial period along the southwest coast of India     

Kamlesh Verma  M Sudhakar 《Journal of Earth System Science》2006,115(6):695-702

A gravity core collected from the upper slope of southwest of Quilon at a water depth of 776 m (Lat: 8°12′263″N, Long: 76°28′281″E) was analysed for texture (carbonate free), calcium carbonate and organic carbon. Variation in silicic fraction seems to be controlled by silt, i.e., enrichment from 15 ka BP to 10 ka BP and then constant in Holocene. Below 15 ka BP, the silicic fraction gets depleted compared to the Holocene section with a minimum around 21 ka BP. Clay content remains nearly constant except in the Holocene where it shows an enrichment. Carbonate content of less than 63 micron when computed by subtracting coarse fraction content from the total carbonate suggests that the total carbonates are mainly concentrated in the finer fraction. All these carbonate phases show an inverse relationship with silicic fraction except in Holocene. Below 15 ka BP, CaCO₃ dominates in sediments comprising more than 65%, such an increase is also seen in the coarse fraction. Coarse fraction from these sections contains abundant nodular type aggregates encrusting small forams. This period is marked by a high sedimentation rate comparable to Holocene. These parameters suggest that the productivity and precipitation have increased in the Holocene due to the intensification of the southwest monsoon. During the last glacial maximum and early deglacial period the high sedimentation rate indicates redeposition of the carbonates from the existing carbonate lithofacies situated between Quilon and Cape Comorin probably due to the slope instability.  相似文献   

Sixteen Statistical Tests for Outlier Detection and Rejection in Evaluation of International Geochemical Reference Materials: Example of Microgabbro PM-S   总被引：2，自引：0，他引：2  

Surendra P. Verma 《Geostandards and Geoanalytical Research》1997,21(1):59-75

A totally objective procedure involving sixteen statistical tests (a total of thirty four single or multiple outlier versions of these tests) for outlier detection and rejection in a univariate sample is applied to a data base of sixty four elements in a recently issued international geochemical reference material (RM), a microgabbro PM-S from Scotland. This example illustrates the relative importance and usefulness of these tests in processing modern geochemical data for possible outliers and obtaining mean concentration and other statistical parameters from a final normal sample of univariate data. The final mean values are more reliable (characterized by smaller standard deviations and narrower confidence limits) than those obtained earlier using an accommodation approach (robust techniques) applied to this data base. Very high quality (certified value equivalent, cve) mean data are now obtained for eleven elements as well as high quality recommended values (rv) for thirty three elements in PM-S. Earlier work using the accommodation approach failed to establish even one cve value for any of the sixty four elements compiled here. The present procedure of outlier detection and elimination is therefore recommended in the study of RMs  相似文献   

A modal pushover analysis procedure to estimate seismic demands for unsymmetric‐plan buildings     

Anil K. Chopra  Rakesh K. Goel 《地震工程与结构动力学》2004,33(8):903-927

An Erratum has been published for this article in Earthquake Engng. Struct. Dyn. 2004; 33:1429. Based on structural dynamics theory, the modal pushover analysis (MPA) procedure retains the conceptual simplicity of current procedures with invariant force distribution, now common in structural engineering practice. The MPA procedure for estimating seismic demands is extended to unsymmetric‐plan buildings. In the MPA procedure, the seismic demand due to individual terms in the modal expansion of the effective earthquake forces is determined by non‐linear static analysis using the inertia force distribution for each mode, which for unsymmetric buildings includes two lateral forces and torque at each floor level. These ‘modal’ demands due to the first few terms of the modal expansion are then combined by the CQC rule to obtain an estimate of the total seismic demand for inelastic systems. When applied to elastic systems, the MPA procedure is equivalent to standard response spectrum analysis (RSA). The MPA estimates of seismic demand for torsionally‐stiff and torsionally‐flexible unsymmetric systems are shown to be similarly accurate as they are for the symmetric building; however, the results deteriorate for a torsionally‐similarly‐stiff unsymmetric‐plan system and the ground motion considered because (a) elastic modes are strongly coupled, and (b) roof displacement is underestimated by the CQC modal combination rule (which would also limit accuracy of RSA for linearly elastic systems). Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Prediction of creep characteristic of rock under varying environment   总被引：2，自引：0，他引：2  

T. N. Singh  A. K. Verma 《Environmental Geology》2005,48(4-5):559-568

The strain developed due to creep is mainly proportional to the logarithm of the time under load, and is mostly proportional to the stress and temperature. At higher temperature the creep rate falls slowly with respect to time, and the creep strain is proportional to a fractional power of time, with the exponent increasing as the temperature increases and reaching a value approximately one-third at temperatures of about 0.5°C. At these temperatures, the creep increases with stress according to a power greater than unity and possibly exponentially. It increases with temperature as (−U/kT), where U is an activation energy and k is Boltzman’s constant. There are different methods to determine the creep strain and the energy of Jog (B) including experimental methods, multivariate regression analysis, and by numerical simulation. These methods are less cumbersome and time consuming. In the present investigation, artificial neural network technique has been used for prediction of the creep strain and energy of Jog (B). Two different networks have been tested and validated. Both the networks have four input neurons and one hidden layer with five neurons, and one output neuron. The data for different rocks at temperatures up to 750°C under conditions of compressive or tortional stress are taken from the literatures. The training and testing data sets used were 163 and 14, respectively. To deal with the problem of overfitting of data, Bayesian regulation has been used and network is trained with suitable training epochs. The coefficients of correlation among the predicted and observed values are found high and they improve the confidence of the users. The mean absolute percentage error obtained are also very low.  相似文献   

Classification of glacial lakes using integrated approach of DFPS technique and gradient analysis using Sentinel 2A data     

Prateek Verma  Sanjay Kumar Ghosh 《国际地球制图》2019,34(10):1075-1088

It is important to identify and locate glacial lakes for assessing any potential hazard. This study presents a combination of semi-automatic method Double-Window Flexible Pace Search (DFPS) and edge detection technique to identify glacial lakes using Sentinel 2A satellite data. Initially, Normalized Difference Water Index (NDWI) has been used to identify water and non-water areas, while DFPS and Edge detection technique has been used to identify an optimum threshold value to distinguish between water and shadow areas. The optimal threshold from DFPS process is 0.21, while threshold value of gradient magnitude using edge detection process is 0.318. The number of glacial lakes identified using the above algorithm is in close agreement with previously published results on glacial lakes in Gangotri glacier using different techniques. Thus, a combination of DFPS and edge detection process has successfully segregated glacial lakes from other features present in Gangotri glacier.  相似文献   

Dump slope stability analysis – A case study     

Prasanta Kumar Behera  Kripamoy Sarkar  Ashok Kumar Singh  A. K. Verma  T. N. Singh 《Journal of the Geological Society of India》2016,88(6):725-735

In opencast mining operation, the stability of waste materials stands at high priority from the safety and economic perspective. Poor management of overburden (OB) dump results the instability of slope in an opencast mine. The present paper deals with the stability analysis of dump material of an opencast coal mine at Talcher coal field, Angul district, Odisha, by means of different geotechnical parameters and mineralogical composition affecting the dump slope. The prolonged rainfall in the mining area causes dump failure and loss of valuable life and property. A recent dump failure that occurred in 2013 at Basundhara mines of Mahanadi Coalfields Limited (MCL), Odisha, took 14 lives, and created problems for the mining industry. Most of the dump failure that occurs in the study area are mainly due to increase in pore water pressure as a result of rainfall infiltration. The stability of the waste dump was investigated using the limit equilibrium analysis to suggest an economical, sustainable and safe disposal of the dump in the study area.  相似文献   

Estimation of Above Ground Biomass for Central Indian Deciduous Forests Using ALOS PALSAR L-Band Data     

Kiran Chand Thumaty  Rakesh Fararoda  Suresh Middinti  Rajashekar Gopalakrishnan  C. S. Jha  V. K. Dadhwal 《Journal of the Indian Society of Remote Sensing》2016,44(1):31-39

Reliable and accurate estimates of tropical forest above ground biomass (AGB) are important to reduce uncertainties in carbon budgeting. In the present study we estimated AGB of central Indian deciduous forests of Madhya Pradesh (M.P.) state, India, using Advanced Land Observing Satellite – Phased Array type L-band Synthetic Aperture Radar (ALOS-PALSAR) L-band data of year 2010 in conjunction with field based AGB estimates using empirical models. Digital numbers of gridded 1?×?1° dual polarization (HH & HV) PALSAR mosaics for the study area were converted to normalized radar cross section (sigma naught - σ⁰). A total of 415 sampling plots (0.1 ha) data collected over the study area during 2009–10 was used in the present study. Plot-level AGB estimates using volume equations representative to the study area were computed using field inventory data. The plot-level AGB estimates were empirically modeled with the PALSAR backscatter information in HH, HV and their ratios from different forest types of the study area. The HV backscatter information showed better relation with field based AGB estimates with a coefficient of determination (R²) of 0.509 which was used to estimate spatial AGB of the study area. Results suggested a total AGB of 367.4 Mt for forests of M.P. state. Further, validation of the model was carried out using observed vs. predicted AGB estimates, which suggested a root mean square error (RMSE) of ±19.32 t/ha. The model reported robust and defensible relation for observed vs. predicted AGB values of the study area.  相似文献   

Estimating Pile Set-up Using 24-h Restrike Resistance and Computed Static Capacity for PPC Piles Driven in Soft Lousiana Coastal Deposits   总被引：1，自引：0，他引：1  

Jay X. Wang  Neha Verma  Eric J. Steward 《Geotechnical and Geological Engineering》2016,34(1):267-283

In this paper, the CPT-based predicted ultimate pile resistances (R_p) were compared with the measured pile resistances (R_m) at different elapsed time for the piles driven into saturated soft clays where piles displayed significant set-up effect. The measured pile resistances were based on 115 restrike records collected from 95 production piles, and 74 records of 9 tested piles. The predicted ultimate pile resistances were calculated from the LCPC, the Schmertmann, and the de Ruiter–Beringen methods, respectively. With the significant pile set-up effect taken into account, the relationship between measured resistances and predicted capacities at different times after pile installation were investigated. The ratios of the measured pile resistances to the predicted capacities scattered in a large spectrum. The ratios fluctuated and stayed within a range of 0.6–1.6 for different CPT methods since end of initial driving until more than 2 months after pile installation. Plots of the ratios versus the predicted pile capacities using different CPT methods have revealed that the ratio (R_m/R_p) presented a strong dependence on the predicted capacities. Great research efforts have been devoted to the analyses of the ratios of the 24-h measured resistance to the predicted capacity based on different CPT methods, in an attempt to find a feasible empirical correlation. It is found that a simple linear relationship exists between the quad root of the ratio and the predicted capacity. The developed empirical equations will give pile foundation engineers an insight into the ultimate resistances of driven piles demonstrating significant pile set-up effects. Pile set-up makes pile resistances grow with time, and it might be one of the reasons that cause the frequently reported large discrepancy between calculated static capacity and measured resistance at a certain time after pile installation.  相似文献