A dynamical model for the P1 — I1 phase transition in anorthite,CaAl2Si2O8     

G. Van Tendeloo  Subrata Ghose  S. Amelinckx 《Physics and Chemistry of Minerals》1989,16(4):311-319

Electron diffraction and electron microscopic evidence is presented for a dynamical and reversible phase transition in anorthite at T _c=516 K. Antiphase boundaries with a displacement vector, R=1/2[111] become unstable at T _c, while other antiphase boundary loops with the same displacement vector are formed. These interfaces are very mobile and vibrate with a frequency which increases strongly with temperature. At temperatures considerably above T _c, a shimmering effect is observed on imaging in dark field using diffuse c reflections. These observations are in agreement with the interpretation of the high temperature body-centered phase as a statistical dynamical average of very small c type antiphase domains of primitive anorthite. We propose that the c type antiphase domains in primitive anorthite originate from ordered and anti-ordered configurations around Ca²⁺ ions at (ooo) and (oio) [likewise (zoo) and (zio)] positions. The dynamical model for the transition involves a two-stage mechanism: a softmode mechanism causing the aluminosilicate framework to approach body-centered symmetry, followed by an orderdisorder of the Ca²⁺ ion configurations. Close to T _c, statistical fluctuations set in and breathing motion type lattice vibrations of the aluminosilicate framework cause the configurations around Ca (ooo) and Ca(oio) [likewise Ca(zoo) and Ca(zio)] in the configuration to dynamically interchange through an intermediate configuration. The dynamical nature of the phase transition in anorthite is comparable to the — phase transition in quartz.  相似文献   

Chemical characteristics of some basaltic rocks of India     

N. C. Ghose 《Bulletin of Volcanology》1971,35(4):1022-1036

An analysis of the chemical characteristics of about 200 basaltic rocks of India indicate that the rocks of Pavagarh, Girnar, Rajmahal, Mundwara, Cuddapah and Panjal Trap form independent magmatic series of mixed type having entirely different chemical characteristics relative to the Deccan basalt. The tholeiitic and olivine or alkaline basalts do not seem to form independent magma types. The present study indicates that the rocks belonging to the above magma types coexist together and may represent differentiates of a single magma series.  相似文献   

Chemical composition of biotite in the metamorphic and granitic rocks of Richughuta,district Palamau,Bihar (India)     

N.C. Ghose 《Chemical Geology》1971

Partial chemical analyses of eighteen biotite samples along with complete analyses of the respective host rocks were carried out on some metamorphic and granitic rocks of the area around Richughuta in the Palamau district of Bihar. Chemical changes in the biotites show an increase of Ti, Fe, Mn and alkali contents with decrease of Al, Mg and MgO/FeO ratio from schist to granite. The ratio MgO/FeO increases with increase in the oxidation ratio of the host rock.  相似文献   

Luna 20 pyroxenes: exsolution and phase transformation as indicators of petrologic history     

Subrata Ghose  I.Stewart McCallum  Enrique Tidy 《Geochimica et cosmochimica acta》1973,37(4):831-839

Pyroxenes from our sample of Luna 20 soil are predominantly orthopyroxene with subordinate pigeonite. The orthopyroxenes are chromium-rich bronzites and contain submicroscopic lamellae of augite in a twinned orientation exsolved on (100). These lamellae have a composition close to the diopside-hedenbergite join. Asymmetric diffuse streaks parallel to $\text{a}{}^1$ indicate stacking faults parallel to (100) and possibly very thin (10–20 Å) lamellae of clinobronzite parallel to (100). Pigeonite crystals are very complex crystallographically and chemically, with optically visible (001) augite exsolution lamellae and two sets of chromite exsolution lamellae. In addition, there are submicroscopic (100) augite lamellae and a second generation of clinohypersthene lamellae which appear to have exsolved from the (001) augite lamellae. The clinohypersthene host, which has a large number of stacking faults parallel to (100), has partially inverted to hypersthene of the same composition. The hypersthene occurs as very fine lamellae (less than 1000 Å) parallel to the (100) plane of the clinohypersthene. X_D^Fe-Mg values for five host-lamellae pairs in pigeonite K-4 indicate a significant amount of subsolidus readjustment. We tentatively conclude that many of the bronzite and pigeonite crystals were derived from rocks crystallized from a high level magma chamber in the lunar highland crust.  相似文献   

Influence of strong motion characteristics on permanent displacement of slopes   总被引：1，自引：0，他引：1  

Rana Roy  Debasis Ghosh  Gautam Bhattacharya 《Landslides》2016,13(2):279-292

Landslides triggered by moderate to major earthquakes are a recognized seismic hazard. Arias Intensity (I _a) is a key intensity measure of the ground motion, but significant duration is widely used to define strong motion duration. We calculate Newmark’s displacements using earthquake records bracketing a broad range of Arias Intensity and significant duration employing Newmark’s rigid block method and a number of yield accelerations. Total landslide displacement increases with the increase in the energy content of the ground motion (I _a) above a threshold. Such threshold may be expressed as a function of yield acceleration of the slope regardless of the ground motion characteristics. Newmark displacement decreases with increasing duration for earthquakes with similar energy content. The wide scatter in the results converges when using formal dimensional analysis. Self-similar symmetry may facilitate the assessment of the performance of slopes during earthquakes. The mathematical framework for probabilistic determination of landslides displacement may be a useful aid to estimate the likelihood of landslide hazards provided that the geotechnical properties of the slopes are known.  相似文献   

Numerical Analysis of Sill and Crown Pillar Stability for Multilevel Cut and Fill Stopes in Different Geomining Conditions     

Hemant Kumar  Debasis Deb  Debashish Chakravarty 《Geotechnical and Geological Engineering》2016,34(2):529-549

A steeply dipping orebody, having decreasing width with depth has been modeled considering horizontal cut and fill method of stoping at four different depth levels. The focus of the study is to identify and understand the behavior of crown and sill pillars in terms of varying stress and geo-mining conditions without reinforcement using finite element method. Analysis of stresses, displacements and extent of yield zones around the excavation is carried out by varying the rock mass conditions such as geological strength index, uniaxial compressive strength (UCS or σ _ci), modulus of elasticity (E), and thickness of crown and sill pillars (T). These analyses have been conducted based on 135 non-linear numerical models considering Drucker–Prager material model in plane strain condition. Results of the study provide valuable insight into the stress concentration factors of the pillars highlighting stress distributions, roof convergence, yield zones and support requirements. Finally, it suggests the optimum thickness of crown and sill pillar with varying thickness of orebody.  相似文献   

Water Quality Monitoring of Tropical Ponds: Location and Depth Effect in Two Case Studies     

Gautam Mukhopadhyay  Debasis Mondal  Pinaki Biswas  Anjana Dewanji 《洁净——土壤、空气、水》2004,32(2):138-148

The variability in water chemistry of samples taken on a monthly basis (March 1999 to February 2000) from two shallow tropical ponds was studied. The effect of location and pond depth on water chemistry was also examined. The study demonstrated that intraannual variability in nutrient concentration is high. Thus, a high annual sampling frequency is required to provide representative annual mean water quality data. Routine monitoring during the monsoons is important for studies on dissolved oxygen and macrophyte growth. Significant differences were found between the topmost and bottommost points for samples of dissolved oxygen collected from the deepest part of both ponds. For nutrient analysis (nitrogen and phosphorus), sample from any location was found to be representative of the whole pond.  相似文献   

Estimation of Residual Undrained Shear Strength from Gravity Corer Penetration Data     

Chaitanya Vardhan  Debasis Roy 《Marine Georesources & Geotechnology》2006,24(4):305-316

Residual undrained shear strength, s_{u_res}, is an important parameter for analyzing the response of structures buried within potentially unstable soil mass. A framework for estimating s_{u_res} of fine grained sediments from gravity corer penetration has been developed considering viscous drag during free fall of the corer through seawater and cohesive energy loss during sediment penetration. The procedure was used to estimate s_{u_res} using data from a submarine geotechnical investigation in western Canada. Comparison of the results with alternative estimates of s_{u_res} from miniature torvane tests on the gravity core samples and CPTs performed nearby reveals a reasonable agreement.  相似文献   

Interaction of a Shield Structure with Surrounding Rock Strata Under Geo-static and Fatigue Loadings     

Islavath  Sreenivasa Rao  Deb  Debasis 《Geotechnical and Geological Engineering》2022,40(6):2949-2965

Geotechnical and Geological Engineering - Shields are deployed in a longwall panel to support incumbent rock strata and to protect shearer and persons working at the face. Shields undergo repeated...  相似文献   

Cancer risk estimation from dietary arsenic,a new approach from longitudinal cohort study     

Anirban?BiswasEmail author  Arabinda?Das  Debasree?Deb  Aloke?Ghose  Debendra?Nath?Guha Mazumder 《Stochastic Environmental Research and Risk Assessment (SERRA)》2018,32(4):1035-1050

Inorganic arsenic is a carcinogen and consumption in low dose may lead to cancer. We estimated the cancer risk of the participants from arsenic endemic regions of West Bengal, India. The probable cancer risk was estimated following the assessment of daily inorganic arsenic intake through drinking water and diets of 20 participants for three consecutive years who had been using low arsenic water in the Indian context (median arsenic concentration in the study Years-I, II and III were 22, 16, 13 µg/l respectively). Probable cancer risk of the population was 2.80 × 10^?4, 2.94 × 10^?4, 3.12 × 10^?4 in the three respective study years (Year-I, II and III); just higher than the US EPA risk level of concern. The arsenic species content of the paired raw, cooked rice and urine was estimated in the as is taken basis. The major diet component, rice contained 72–86% inorganic arsenic whereas urine contains 70% organic arsenic on an average. The cancer risk assessment has been proposed to be modified by inclusion of urine arsenic release, considering the fact of arsenic release through urine. The risk became 1.28 × 10^?5, 1.13 × 10^?5, 1.01 × 10^?5 in the study Year-I, II and III respectively, considering urinary arsenic release, attributed the consideration of urine arsenic release into probable cancer risk estimation.  相似文献