Lattice dynamics and raman spectroscopy of protoenstatite,Mg2Si2O6     

Subrata Ghose  Narayani Choudhury  S. L. Chaplot  C. Pal Chowdhury  S. K. Sharma 《Physics and Chemistry of Minerals》1994,20(8):625-625

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Morphodynamics of the Kulsi River Basin in the northern front of Shillong Plateau: Exhibiting episodic inundation and channel migration     

Watinaro Imsong  Swapnamita Choudhury  Sarat Phukan  Bhagawat Pran Duarah 《Journal of Earth System Science》2018,127(1):5

The present study is undertaken in the Kulsi River valley, a tributary of the Brahmaputra River that drains through the tectonically active Shillong Plateau in northeast India. Based on the fluvial geomorphic parameters and Landsat satellite images, it has been observed that the Kulsi River migrated 0.7–2 km westward in its middle course in the past 30 years. Geomorphic parameters such as longitudinal profile analysis, stream length gradient index (SL), ratio of valley floor width to valley height (Vf), steepness index (\(k_{s})\) indicate that the upstream segment of the Kulsi River is tectonically more active than the downstream segment which is ascribed to the tectonic activities along the Guwahati Fault. \(^{14}\hbox {C}\) ages obtained from the submerged tree trunks of the Chandubi Lake, which is located in the central part of the Kulsi River catchment suggests inundation (high lake levels) during 160 ± 50 AD, 970 ± 50 AD, 1190 ± 80 AD and 1520 ± 30 AD, respectively. These periods broadly coincide with the late Holocene strengthened Indian Summer Monsoon (ISM), Medieval Warm Period (MWP) and the early part of the Little Ice Age (LIA). The debris which clogged the course of the river in the vicinity of the Chandubi Lake is attributed to tectonically induced increase in sediment supply during high magnitude flooding events.  相似文献   

Recommended Sampling Intervals for Arsenic in Private Wells     

Brian J. Mailloux  Nicholas A. Procopio  Mark Bakker  Therese Chen  Imtiaz Choudhury  Kazi Matin Ahmed  M. Rajib H. Mozumder  Tyler Ellis  Steve Chillrud  Alexander van Geen 《Ground water》2021,59(1):80-89

Geogenic arsenic in drinking water is a worldwide problem. For private well owners, testing (e.g., private or government laboratory) is the main method to determine arsenic concentration. However, the temporal variability of arsenic concentrations is not well characterized and it is not clear how often private wells should be tested. To answer this question, three datasets, two new and one publicly available, with temporal arsenic data were utilized: 6370 private wells from New Jersey tested at least twice since 2002, 2174 wells from the USGS NAWQA database, and 391 private wells sampled 14 years apart from Bangladesh. Two arsenic drinking water standards are used for the analysis: 10 µg/L, the WHO guideline and EPA standard or maximum contaminant level (MCL) and 5 µg/L, the New Jersey MCL. A rate of change was determined for each well and these rates were used to predict the temporal change in arsenic for a range of initial arsenic concentrations below an MCL. For each MCL and initial concentration, the probability of exceeding an MCL over time was predicted. Results show that to limit a person to below a 5% chance of drinking water above an MCL, wells that are ½ an MCL and above should be tested every year and wells below ½ an MCL should be tested every 5 years. These results indicate that one test result below an MCL is inadequate to ensure long-term compliance. Future recommendations should account for temporal variability when creating drinking water standards and guidance for private well owners.  相似文献   

The role of undirected relativistic electrons with inertia in the formation of weakly relativistic ion acoustic solitons in magnetized plasma     

B. C. Kalita  M. Choudhury 《Astrophysics and Space Science》2013,346(2):375-382

Existence of both subsonic and supersonic compressive solitons of interesting characters is established in this magnetized plasma model with non relativistic ions and relativistic electrons. The small supersonic range for the generation of compressive solitons is shown to confine near the vicinity of the direction of the magnetic field. It is predicted that the relativistic variation of electron’s mass is responsible for the expansion of Sagdeev potential to result increase in soliton’s amplitude and decrease in its width.  相似文献   

Post-seismic deformation associated with the 2001 Bhuj earthquake     

Pallabee Choudhury  J. K. Catherine  V. K. Gahalaut  Sumer Chopra  Rakesh Dumka  Ketan Singha Roy 《Natural Hazards》2013,65(2):1109-1118

We report the results of GPS measurements of post-seismic deformation due to the 2001 Bhuj earthquake in the Kachchh region, western India. The estimated horizontal velocity vectors in ITRF05 are in the range of 48?C49?mm/year in N46?C50°E. The observed velocity at the Gandhinagar permanent site, a far off site from the earthquake source region and probably unaffected by the post-seismic deformation, is 49?±?1?mm/year in N47°E, which is consistent with the predicted motion of Indian plate at Gandhinagar. At other sites in the source region, transient post-seismic deformation is found to be low; it attenuated rapidly within 3?C4?years of the earthquake and is much low now. Our results support the idea that mantle rheology is weak in the region.  相似文献   

Determination of column size for displacement‐based design of reinforced concrete frame buildings          下载免费PDF全文

S. S. Mayengbam  S. Choudhury 《地震工程与结构动力学》2014,43(8):1149-1172

This article reports a method to determine the storey‐wise column size for displacement‐based design of reinforced concrete frame buildings with a wide range of storey drift and building plan. The method uses a computer program based algorithm. The basic relation used in the algorithm is formulated by considering the various possible deformation components involved in the overall frame deformation. As a necessity to represent the deformation component due to plastic rotation of beam members, a relation between the beam plastic rotation and the target‐drift is adopted. To control the dynamic amplification of interstorey drift, a target‐drift dependant design‐drift reduction factor is used. The dynamic amplification of column moment is accounted with the help of an approximate conversion of fundamental period of the building from the effective period of the equivalent SDOF system. To avoid the formation of plastic hinge in column members, a design‐drift dependant column–beam moment capacity ratio is used. The method successfully determines the storey‐wise column size for buildings of four plans of different varieties, heights up to 12 storeys and target‐drift up to 3%. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Magnetoelastic shear waves in an infinite self-reinforced plate     

A. Chattopadhyay  S. Choudhury 《国际地质力学数值与分析法杂志》1995,19(4):289-304

The propagation of magnetoelastic shear waves in an infinite self-reinforced plate is studied in this paper. The frequency spectrum for SH-modes in the plate is drawn and it is shown that if the dimensionless wave number is real, the branches are hyperbolas while for imaginary wave numbers, they are ellipses. It is also observed that for higher modes, the dimensionless group velocity approaches 9·9754 as the wave number increases. The group velocity is normalized with respect to the phase velocity of shear waves. For a homogeneous and isotropic medium, on the other hand, the dimensionless group velocity approaches unity. So it is approximately 10 times larger in case of magnetoelastic shear waves in an infinite self-reinforced plate. It is also noted that in a reinforced medium, if both the values of the coupling parameter and the angle at which the wave crosses the primary magnetic field are increased, the values of the dimensionless frequency and group velocity are decreased.  相似文献   

Satellite and In Situ Observations of a Phytoplankton Bloom from Coastal Bay of Bengal: Role in pCO<Subscript>2</Subscript> Modulation     

Rajdeep Roy  K. H. Rao  T. Preethi Latha  Vinay Kumar Dadhwal  V. V. S. S. Sarma  P. V. Nagamani  S. B. Choudhury  Seetharam Pondala 《Journal of the Indian Society of Remote Sensing》2017,45(3):513-524

A phytoplankton bloom was monitored in coastal waters of Bay of Bengal and its influence in water column properties was investigated. Significant draw down of CO₂ was noted within the vicinity of the bloom associated with high chlorophyll biomass. Microscopic analysis revealed diatoms as the dominant population. Skeletonema costatum a diatom, reached cell density of 36,898 cells l^?1 within the bloom. The lowest surface pCO₂ observed was 287 µatm at the southern end of the transect covarying with surface chlorophyll of 1.090 µg l^?1. At the northern end the surface pCO₂ went as low as 313 µatm. The pCO₂ levels below the mixed layer increased twice of that of surface value (~600 µatm). The chlorophyll values observed by Ocean Colour Monitor-2 were modestly related with the in situ measurements. The primary productivity derived from growth rate, assimilation number and maximum surface chlorophyll was 160.6 mg C m^?2 day^?1 leading to a modest sequestration ~of 0.08 Gg of carbon per day by the surface waters. Our observations reflects the potential role of diatom blooms on coastal carbon dynamics therefore should be carefully monitored in realm of anthropogenic changes.  相似文献   

Climate change vulnerability to agrarian ecosystem of small Island: evidence from Sagar Island,India     

Mandal  S.  Satpati  L. N.  Choudhury  B. U.  Sadhu  S. 《Theoretical and Applied Climatology》2018,132(1-2):451-464

Theoretical and Applied Climatology - The present study assessed climate change vulnerability in agricultural sector of low-lying Sagar Island of Bay of Bengal. Vulnerability indices were estimated...  相似文献   

Geochemistry and petrogenesis of anorogenic(?) granitoids of west Garo Hills,Meghalaya     

D. K. Choudhury  A. K. Pradhan  S. Zakaulla  K. Umamaheswar 《Journal of the Geological Society of India》2012,80(2):276-286

The granite in Samingiri — Dilsekgiri area occurs as discordant, isolated pluton within the migmatitic terrain of West Garo Hills district, Meghalaya. The pluton is exposed over 140 sq km (18 km × 8 km). It exhibits structures of solid state and piecemeal stoping effect proximal to the contact and enveloped by a contact metamorphic aureole of albite-epidote-hornfels facies. Modally, it is biotite-monzogranite and biotite-syenogranite with minor biotite, chlorite, epidote and sericite and accessories like zircon, apatite, allanite, pyrite, magnetite and sphene. Geochemically, it is marked by restricted composition (69–76 wt% SiO₂), high alkalies, low Ca, metaluminous to strongly peraluminous (Molar Al₂O₃/CaO+Na₂O+K₂O = 0.95 ? 1.54), high FeO/MgO, high Ga/Al, high contents of Rb, Sr, Ba, Y, Zr and Ce and depleted in Ti and P. The field observation, mineralogical and geochemical aspects indicate the post-tectonic nature of West Garo pluton more like as A-type granite formed by partial melting of lower crustal blocks followed by low to moderate degree of fractional differentiation. Low Ca, alkaline nature and peraluminous character point to A-type nature of West Garo granite significantly different from other granites of Meghalaya Plateau. Rb-Sr age (616±86 Ma) of granite, however, corresponds to widespread Middle to Upper Pan African activity, a thermal event prevailed during Late Proterozoic — Early Palaeozoic (500–800 Ma) period, manifested in the form of several granitic intrusions in the basement gneissic complex and the overlying Proterozoic metasediments of the Shillong Group in Meghalaya Plateau.  相似文献