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31.
Manganese oxide ore from the Bonai‐Keonjhar belt of Odisha, India, has been qualitatively assessed through Raman and FTIR spectroscopy, and X‐ray diffraction. Three categories of ore, namely, high‐grade (MnO2: >72%), medium‐grade (MnO2: 55‐72%) and low‐grade (MnO2:40‐55%) from four mine profiles, Purnapani, Joda West, Khandbandh and Bamebariwere, were collected and subjected to vibrational spectroscopic studies. The use of Raman analysis in the microscopic configuration allowed the spectra to be taken at different points on the polished ore. Besides the Raman features of the ß‐MnO2(Pyrolusite) phases, other signals were assigned to isolated FeO ions accommodated in vacancies and to some aluminium silicates. The three grades of ore show different Raman spectra. The FTIR spectra also exhibit contrasting pattern in different grade sample and support these findings. This study demonstrates the use of vibrational spectroscopy to assess the quality of Mn‐oxide ore that could provide a substitute to cumbersome wet chemical analysis 相似文献
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33.
S. Mohapatra 《地球物理与天体物理流体动力学》2013,107(5):347-374
Scattering of oblique incident waves by small bottom undulation in a two-layer fluid, where the upper layer has a thin ice-cover while the lower one has the undulation, is investigated within the framework of linearized water wave theory. The ice-cover is being modeled as an elastic plate of very small thickness. There exist two modes of time-harmonic waves–one with lower wave number propagating along the ice-cover (ice-cover mode) and the other with higher wave number along the interface (interfacial mode). A perturbation analysis is employed to solve the corresponding boundary value problem governed by modified Helmholtz equation and thereby evaluating the reflection and transmission coefficients approximately up to first order for both modes. A patch of sinusoidal ripples, having two different wave numbers over two consecutive stretches, is considered as an example and the related coefficients are determined. It is observed that when the wave is incident on the ice-cover surface we always find energy transfer to the interface, but for interfacial incident waves there are parameter ranges for which no energy transfer to the ice-cover surface is possible. Also it is observed that for small angles of incidence, the reflected energy is more as compared to the other angles of incidence. These results are demonstrated in graphical form. From the derived results, the solutions for problems with free surface can be obtained as particular cases. 相似文献
34.
Outcrop of wad, about 3–5 m thick, associated with low to medium-grade manganese ore deposits in Iron Ore Group (IOG), is present in large quantum in Bonai-Keonjhar belt, Orissa. It is often inter-bedded with volcanic ash layers. Wad is powdery, fine grained, black to blackish-brown in colour, very soft, readily soils the fingers and its hardness on the Mohs’ hardness scale is 1–3. The wad zone is capped by a thin lateritic zone and overlies manganese ore beds of variable thickness in Dalki, Guruda and Dubna mines. Wad constitutes two mineral phases, viz. manganese oxides (δ-MnO2, manganite, romanechite with minor pyrolusite) and iron oxides (goethite/limonite and hematite) with minor clay and free quartz. Mixed limonite-clay and cryptomelane-limonite are commonly observed. Under microscope the ore appears oolitic, pisolitic, elipsoidal to globular in shape having small detritus of quartz, pyrolusite / romanechite and hematite at the core. The ore contains around 23% Mn and 28% Fe with ～7% of combined alumina and silica. Wad might have developed in a swampy region due to slow chemical precipitation of Fe-Mn-Co enriched fluid, nucleating over quartz/hematite grains. Influence of a marine environment is indicated from δ-MnO2 phase. Remnants of some microfossils, like algal filament, bacteria, foraminifera and diatomite are observed in wad sample under SEM. These microorganisms might have been responsible for the oxidation of dissolved Mn2+ and Fe2+ precipitates. These findings suggest biochemogenic origin of wad in Bonai-Keonjhar belt of Orissa. 相似文献
35.
A. J. Litta U. C. Mohanty S. Kiran Prasad M. Mohapatra Ajit Tyagi S. C. Sahu 《Natural Hazards》2012,61(3):1219-1242
A severe thunderstorm produced a tornado (F3 on the Fujita-Pearson scale), which affected Rajkanika block of Kendrapara district
of Orissa in the afternoon of March 31, 2009. The devastation caused by the tornado consumed 15 lives and left several injured
with huge loss of property. The meteorological conditions that led to this tornado have been analyzed. An attempt is also
made to simulate this rare event using Non-hydrostatic Mesoscale Model (NMM) core of the Weather Research and Forecasting
(WRF) system with a spatial resolution of 4 km for a period of 24 h, starting at 0000 UTC of March 31, 2009. The atmospheric
settings resulted from synoptic, surface, upper air, satellite and radar echo studies were favorable for the occurrence of
a severe thunderstorm activity over Rajkanika. The model-simulated meteorological parameters are consistent with each other,
and all are in good agreement with the observation in terms of the region of occurrence of the intense convective activity.
The model has well captured the vertical motion. The core of the strongest winds is shown to be very close to the site of
actual occurrence of the event. The wind speed is not in good agreement with the observation as it has shown the strongest
wind of only 20 ms−1, against the estimated wind speed of 70 ms−1. The spatial distributions as well as intensity of rainfall rates are in good agreement with the observation as model simulated
35.4 mm against the observed rainfall of 41 mm over Chandbali. The results of these analyses demonstrated the capability of
high-resolution WRF–NMM model in simulation of severe thunderstorm events. 相似文献
36.
M. Mohapatra G. S. Mandal B. K. Bandyopadhyay Ajit Tyagi U. C. Mohanty 《Natural Hazards》2012,63(3):1601-1620
Hazards associated with tropical cyclones are long-duration rotatory high-velocity winds, very heavy rain and storm tide. India has a coastline of about 7,516?km of which 5,400?km is along the mainland. The entire coast is affected by cyclones with varying frequency and intensity. The India Meteorological Department (IMD) is the nodal government agency that provides weather services related to cyclones in India. However, IMD has not identified cyclone-prone districts following any specific definition though the districts for which cyclone warnings are issued have been identified. On the other hand, for the purpose of better cyclone disaster management in the country, it is necessary to define cyclone proneness and identify cyclone-prone coastal districts. It is also necessary to decide degree of hazard proneness of a district by considering cyclone parameters so that mitigation measures are prioritised. In this context, an attempt has been made to prepare a list of cyclone hazard prone districts by adopting hazard criteria. Out of 96 districts under consideration, 12, 45, 31 and 08 districts are in very high, high, moderate and low categories of proneness, respectively. In general, the coastal districts of West Bengal, Orissa, Andhra Pradesh and Tamil Nadu are more prone and are in the high to very high category. The cyclone hazard proneness factor is very high for the districts of Nellore, East Godawari, and Krishna in Andhra Pradesh; Yanam in Puducherry; Balasore, Bhadrak, Kendrapara and Jagatsinghpur in Orissa; and South and North 24 Parganas, Medinipur and Kolkata in West Bengal. The results give a realistic picture of degree of cyclone hazard proneness of districts, as they represent the frequency and intensity of land falling cyclones along with all other hazards like rainfall, wind and storm surge. The categorisation of districts with degree of proneness also tallies with observed pictures. Therefore, this classification of coastal districts based on hazard may be considered for all the required purposes including coastal zone management and planning. However, the vulnerability of the place has not been taken into consideration. Therefore, composite cyclone risk of a district, which is the product of hazard and vulnerability, needs to be assessed separately through detailed study. 相似文献
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Climate Dynamics - The Tropical Indian Ocean (TIO) is seen to exhibit robust warming after the 1950s. Most of the previous studies on the Indian Ocean (IO) surface and subsurface temperature... 相似文献
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Large volume of iron oxy-hydroxide minerals occur in association with manganese oxide phase in manganese ores of the Eastern
Ghats Supergroup, Koraput district, Orissa. On the basis of OH content, the iron mineral can be classified into hydrohematite,
goethite, and hydrogoethite. These minerals exhibit eight types of microstructures such as ooloidal, caterpillar, disseminated,
reniform, worm, mosaic, globular and spherulitic. Chemical composition of such micro-structures obtained through EPMA, distinguishes
them into three domains, developed under different environment. Hydrohematite, having 8–10 % H2O, characteristically contains higher pc of manganese (>5%) and phosphorous (>0.6%) but have low silica and alumina. These
are formed syngenetically with Mn-oxide minerals in a manganese rich paragenesis. Goethite containing 11 to 12% water, has
relatively low level of manganese and phosphorous, and formed in a later period, as secondary open space filling. Hydrogoethite
shows very high water content (>16%), almost devoid of manganese, and impoverished in phosphorous but having higher percentage
of alumina, silica and appreciable copper and nickel. This was latest to form in the zone of oxidation under supergene condition. 相似文献
39.
Detrital type of manganese ore bodies in the Precambrian Iron Ore Group of rocks occur in the Bonai-Keonjhar belt, Orissa
besides stratiform (bedded type) and stratabound-replacement types of deposits. These ores appear in form of large boulders
within lateritised aprons at various depths, often reaching beyond 30 m from the surface. Overprinting of primary structures,
presence of mixed Fe-clasts and Mnooliths/pisoliths, mineral species of different generations and wide chemical variation
amongst morphological varieties and from boulder to boulder are the characteristic hallmarks of such ore bodies. Features
associated with ores occurring in different morphologies, namely: spongy, platy, recemented, and massive varieties from a
typical profile of Orahari Mn-ore body in Keonjhar district are described. Recemented variety may be further classified into
sub-varieties such as canga, agglomerate, and mangcrete. Common primary Fe-minerals are hematite, martite with relict magnetite.
The secondary Fe-Mn phases are goethite, specularite, cryptomelane, lithiophorite, chalcophanite, manganite, and pyrolusite.These
are ore bodies of allochthonous nature developed through a number of stages during terrain evolution and lateritisation. Secondary
processes such as reworking of pre-existing crust through remobilisation, solution, precipitation, cementation, transport,
etc. are responsible for the development of such detrital ore bodies in the Bonai-Keonjhar belt of Eastern India. 相似文献
40.
Evaluation of operational tropical cyclone intensity forecasts over north Indian Ocean issued by India Meteorological Department 总被引：2，自引：2，他引：0
India Meteorological Department (IMD) introduced the objective tropical cyclone (TC) intensity forecast valid for next 24 h over the north Indian Ocean (NIO) in 2003 and extended up to 72 h in 2009. In this study, an attempt is made to evaluate the TC intensity forecast issued by IMD during 2005–2011 (7 years) by calculating the absolute error (AE), root mean square error (RMSE) and skill in intensity forecast in terms of maximum sustained surface wind (MSW). The accuracy of TC intensity forecast has been analysed with respect to basin of formation (Bay of Bengal, Arabian Sea and NIO as whole), season of formation (pre-monsoon and post-monsoon seasons), intensity of TCs (cyclonic storm and severe cyclonic storm or higher intensities) and type of track of TCs (climatological/straight moving and recurving/looping type). The study shows that the average AE (RMSE) in intensity forecast is about 11(14), 14(19) and 20(26) knots, respectively, for 24-, 48- and 72-h forecasts over the NIO as a whole during 2009–2011. The skill of intensity forecast is about 44 %(48 %), 60 %(58 %) and 60 %(65 %) for 24-, 48- and 72-h forecasts during 2009–2011 with respect to AE (RMSE). There is no significant improvement in terms of reduction in AE and RMSE of MSW forecast over the NIO like that over the northwest Pacific and northern Atlantic Oceans during 2005–2011. However, the skill in intensity forecast compared to persistence method has significantly improved by about 6 %(10 %) and 9 %(8 %) per year, respectively, for 12- and 24-h forecasts considering the AE (RMSE) during 2005–2011. There is also significant increasing trend in percentage of 24-h intensity forecasts with error of 10 knots or less during 2005–2011. 相似文献