Phase-field study of grain boundary tracking behavior in crack-seal microstructures     

Kumar Ankit  Britta Nestler  Michael Selzer  Mathias Reichardt 《Contributions to Mineralogy and Petrology》2013,166(6):1709-1723

In order to address the growth of crystals in veins, a multiphase-field model is used to capture the dynamics of crystals precipitating from a super-saturated solution. To gain a detailed understanding of the polycrystal growth phenomena in veins, we investigate the influence of various boundary conditions on crystal growth. In particular, we analyze the formation of vein microstructures resulting from the free growth of crystals as well as crack-sealing processes. We define the crystal symmetry by considering the anisotropy in surface energy to simulate crystals with flat facets and sharp corners. The resulting growth competition of crystals with different orientations is studied to deduce a consistent orientation selection rule in the free-growth regime. Using crack-sealing simulations, we correlate the grain boundary tracking behavior depending on the relative rate of crack opening, opening trajectory, initial grain size, and wall roughness. Further, we illustrate how these parameters induce the microstructural transition between blocky (crystals growing anisotropically) to fibrous morphology (isotropic) and formation of grain boundaries. The phase-field simulations of crystals in the free-growth regime (in 2D and 3D) indicate that the growth or consumption of a crystal is dependent on the orientation difference with neighboring crystals. The crack-sealing simulation results (in 2D and 3D) reveal that crystals grow isotropically and grain boundaries track the opening trajectory if the wall roughness is high, opening increments are small, and crystals touch the wall before the next crack increment starts. Further, we find that within the complete crack-seal regime, anisotropy in surface energy results in the formation of curved/oscillating grain boundaries (instead of straight) when the crack-opening velocity is increased and wall roughness is not sufficiently high. Additionally, the overall capability of phase-field method to simulate large-scale polycrystal growth in veins (in 3D) is demonstrated enumerating the main advantages of adopting the novel approach.  相似文献   

Methane emission modelling using MODIS thermal and optical data: A case study on Gujarat     

Reshu Agarwal  J. K. Garg 《Journal of the Indian Society of Remote Sensing》2007,35(4):323-331

Wetlands are one of the most important sources of atmospheric methane (CH₄) contributing about 22% to the global methane budget. But to improve estimates of CH₄ emission at regional and global scales there is a need to observe the sources such as wetlands frequently and develop process-based models. In this regard, wetland inventory using satellite remote sensing data has conventionally been carried out by analysis of optical data. Due to thermal inertia differences emittive thermal channels data has shown promise to provide highly critical information about wetlands such as water spread, aquatic vegetation and mud flats etc. Thermal channels data of MODIS (Moderate Resolution Imaging Spectroradiometer) sensor with a spatial resolution of 1km and swath of 2330 km is emerging as the key source of remote sensing data for global/ regional wetland estimation and assessment of green house gas emission. In the present study MODIS thermal channels (31 and 32) and optical channels (1,2, and 3) data have been used for evaluating methane emission from wetlands in Gujarat. An empirical model based on temperature and productivity has been used to investigate the response of methane emission from different sources. Model has the potential to estimate country level methane emission based on satellite remote sensing in conjunction with collateral data/information. In this study. MODIS data of two dates pertaining to Gujarat have been analyzed and results compared with respect to methane emission.  相似文献   

Use of fuzzy synthetic evaluation for assessment of groundwater quality for drinking usage: a case study of Southern Haryana,India   总被引：1，自引：0，他引：1  

Bhupinder Singh  Sudhir Dahiya  Sandeep Jain  V. K. Garg  H. S. Kushwaha 《Environmental Geology》2008,54(2):249-255

A method based on concept of fuzzy set theory has been used for decision-making for the assessment of physico-chemical quality of groundwater for drinking purposes. Conventional methods for water quality assessment do not consider the uncertainties involved either in measurement of water quality parameters or in the limits provided by the regulatory bodies. Fuzzy synthetic evaluation model gives the certainty levels for the quality class of the water based on the prescribed limit of various regulatory bodies and opinion of the experts from the field of drinking water quality. In this paper, application of fuzzy rule based optimization model is illustrated with twenty groundwater samples from Sohna town of Gurgaon district of Southern Haryana, India. These samples were analysed for 15 different physico-chemical parameters, out of them nine important parameters were used for the quality assessment using fuzzy synthetic evaluation approach. From this study, it has been concluded that all the water samples are in acceptable category whose certainty level ranges from 44 to 100%. Water from these sources can be used for the drinking purposes if alternate water source is not available without any health concern on the basis of physico-chemical characteristics.  相似文献   

Impact study by various bridge models     

A. Wiriyachai  Kaung-Han Chu  V. K. Garg 《地震工程与结构动力学》1982,10(1):31-45

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Fatigue life of critical members in a railway truss bridge     

Vijay K. Garg  Kuang-Han Chu  A. Wiriyachai 《地震工程与结构动力学》1982,10(6):779-795

The fatigue life of critical members, such as hangers, floor-beams and stringers in a single track, open deck railroad truss bridge, was investigated for various unit freight trains, operating at different speeds. A partial bridge model was used, along with a three-car train, to determine the stress cycles. For determining the fatigue lives of critical members, four fully-loaded trains per day were assumed to pass over the bridge. Each train was assumed to consist of one hundred 70-ton cars or seventy 100-ton cars. The 100-ton freight cars cause large stress ranges, and consequently shorter fatigue lives than the 70-ton freight cars. For the hundred-car train, with 70-ton and 100-ton cars mixed in various proportions, the fatigue lives became shorter as the percentage of 100-ton cars in the consist was increased. The impact percentages were also studied.  相似文献   

A study of railway bridge/vehicle interaction and evaluation of fatigue life     

V. K. Garg  K. H. Chu  T. L. Wang 《地震工程与结构动力学》1985,13(6):689-709

A new vehicle model and the partial bridge model were used to study the dynamic interaction between an open deck steel truss bridge and a moving freight train. The responses in terms of dynamic stresses in certain critical members in the bridge were generated to predict their fatigue lives by using a reliability-based methodology.  相似文献   

Retrieval of land surface temperature from Landsat 8 TIRS for the command area of Mula irrigation project     

Bhaskar R. Nikam  Furkat Ibragimov  Arpit Chouksey  Vaibhav Garg  S. P. Aggarwal 《Environmental Earth Sciences》2016,75(16):1169

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Observations of trace gases and aerosols over the Indian Ocean during the monsoon transition period     

T. K. Manual  Ateef Khan  Y. Nazeer Ahammed  R. S. Tanwar  R. S. Parmar  K. S. Zalpuri  Prabhat K. Gupta  S. L. Jain  Risal Singh  A. P. Mitra  S. C. Garg  A. Suryanarayana  V. S. N. Murty  M. Dileep Kumar  Andrew J. Shepherd 《Journal of Earth System Science》2006,115(4):473-484

Characteristics of trace gases (O₃, CO, CO₂, CH₄ and N₂O) and aerosols (particle size of 2.5 micron) were studied over the Arabian Sea, equatorial Indian Ocean and southwest part of the Bay of Bengal during the monsoon transition period (October–November, 2004). Flow of pollutants is expected from south and southeast Asia during the monsoonal transition period due to the patterns of wind flow which are different from the monsoon period. This is the first detailed report on aerosols and trace gases during the sampled period as the earlier Bay of Bengal Experiment (BOBMEX), Arabian Sea Monsoon Experiment (ARMEX) and Indian Ocean Experiments (INDOEX) were during monsoon seasons. The significant observations during the transition period include: (i) low ozone concentration of the order of 5 ppbv around the equator, (ii) high concentrations of CO₂, CH₄ and N₂O and (iii) variations in PM2.5 of 5–20μg/m³.  相似文献   

Ecotourism and its impact on indigenous people and their local environment: case of Ghalegaun and Golaghat of Nepal     

K C  Anup  Ghimire  Sanjeet  Dhakal  Ankit 《GeoJournal》2021,86(6):2747-2765

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Progress in Remediation of Groundwater at Petroleum Sites in California     

Thomas E. McHugh  Poonam R. Kulkarni  Charles J. Newell  John A. Connor  Sanjay Garg 《Ground water》2014,52(6):898-907

Quantifying the overall progress in remediation of contaminated groundwater has been a significant challenge. We utilized the GeoTracker database to evaluate the progress in groundwater remediation from 2001 to 2011 at over 12,000 sites in California with contaminated groundwater. This paper presents an analysis of analytical results from over 2.1 million groundwater samples representing at least $100 million in laboratory analytical costs. Overall, the evaluation of monitoring data shows a large decrease in groundwater concentrations of gasoline constituents. For benzene, half of the sites showed a decrease in concentration of 85% or more. For methyl tert‐butyl ether (MTBE), this decrease was 96% and for TBE, 87%. At remediation sites in California, the median source attenuation rate was 0.18/year for benzene and 0.36/year for MTBE, corresponding to half‐lives of 3.9 and 1.9 years, respectively. Attenuation rates were positive (i.e., decreasing concentration) for benzene at 76% of sites and for MTBE at 85% of sites. An evaluation of sites with active remediation technologies suggests differences in technology effectiveness. The median attenuation rates for benzene and MTBE are higher at sites with soil vapor extraction or air sparging compared with sites without these technologies. In contrast, there was little difference in attenuation rates at sites with or without soil excavation, dual phase extraction, or in situ enhanced biodegradation. The evaluation of remediation technologies, however, did not evaluate whether specific systems were well designed or implemented and did not control for potential differences in other site factors, such as soil type.  相似文献