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333 results on '"Gupta, Prabhat K."'

5. Viscosity of Silica and Doped Silica Melts: Evidence for a Crossover Temperature

Author

Mauro, John C., Kurkjian, Charles R., Gupta, Prabhat K., and Kob, Walter

Subjects
Condensed Matter - Materials Science, Condensed Matter - Disordered Systems and Neural Networks
Abstract

Silica is known as the archetypal strong liquid, exhibiting an Arrhenius viscosity curve with a high glass transition temperature and constant activation energy. However, given the ideally isostatic nature of the silica network, the presence of even a small concentration of defects can lead to a significant decrease in both the glass transition temperature and activation energy for viscous flow. To understand the impact of trace level dopants on the viscosity of silica, we measure the viscosity-temperature curves for seven silica glass samples having different impurities, including four natural and three synthetic samples. Depending on the type of dopant, the glass transition temperature can vary by nearly 300 K. A common crossover is found for all viscosity curves around ~2200-2500 K, which we attribute to a change of the transport mechanism in the melt from being dominated by intrinsic defects at high temperature to dopant-induced defects at low temperatures.

Published
2021

6. Basis Glass States: New Insights from the Potential Energy Landscape

Author

Gupta, Prabhat K. and Kob, Walter

Subjects
Condensed Matter - Disordered Systems and Neural Networks, Condensed Matter - Materials Science, Condensed Matter - Statistical Mechanics
Abstract

Using the potential energy landscape formalism we show that, in the temperature range in which the dynamics of a glass forming system is thermally activated, there exists a unique set of "basis glass states" each of which is confined to a single metabasin of the energy landscape of a glass forming system. These basis glass states tile the entire configuration space of the system, exhibit only secondary relaxation and are solid-like. Any macroscopic state of the system (whether liquid or glass) can be represented as a superposition of basis glass states and can be described by a probability distribution over these states. During cooling of a liquid from a high temperature, the probability distribution freezes at sufficiently low temperatures describing the process of liquid to glass transition. The time evolution of the probability distribution towards the equilibrium distribution during subsequent aging describes the primary relaxation of a glass., Comment: 19 pages

Published
2019

15. Enthalpy landscapes and the glass transition

Author

Mauro, John C., Loucks, Roger J., Varshneya, Arun K., Gupta, Prabhat K., Barth, Timothy J., editor, Griebel, Michael, editor, Keyes, David E., editor, Nieminen, Risto M., editor, Roose, Dirk, editor, Schlick, Tamar, editor, Yip, Sidney, editor, and de la Rubia, Tomás Diaz, editor

Published
2009
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21. Methane Emission Studies and Estimate from Indian Paddy Fields

Author

Parashar, D. C., Mitra, A. P., Gupta, Prabhat K., Rai, J., Sharma, R. C., Singh, N., Kaul, S., Ray, H. S., Das, S. N., Parida, K. M., Rao, S. B., Kanungo, S. P., Ramasami, T., Nair, B. U., Swami, M., Singh, G., Gupta, S. K., Singh, A. R., Saikia, B. K., Barua, A. K. S., Pathak, M. G., Iyer, C. S. P., Gopalakrishnan, M., Sane, P. V., Singh, S. N., Banerjee, R., Sethunathan, N., Adhya, T. K., Rao, V. R., Palit, P., Saha, A. K., Purkait, N. N., Chaturvedi, G. S., Sen, S. P., Sen, M., Sarkar, B., Banik, A., Subharaya, B. H., Lal, S., Venkatramani, S., Lal, G., Chaudhary, A., Sinha, S. K., van Ham, J., editor, Janssen, L. J. H. M., editor, and Swart, R. J., editor

Published
1994
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43. Role of dynamic heterogeneities in crystal nucleation kinetics in an oxide supercooled liquid.

Author

Gupta, Prabhat K., Cassar, Daniel R., and Zanotto, Edgar D.

Subjects
*RATE of nucleation, *SUPERCOOLED liquids, *TEMPERATURE effect, *LITHIUM silicates, *OXIDES
Abstract

The temperature at which the classical critical nucleus size is equal to the average size of the cooperatively rearranging regions (CRR) in a supercooled liquid has been referred to as a "cross-over" temperature. We show, for the first time, using published nucleation rate, viscosity, and thermophysical data, that the cross-over temperature for the lithium disilicate melt is significantly larger than the temperature of the kinetic spinodal and is equal or close to the temperature corresponding to the maximum in the experimentally observed nucleation rates. We suggest that the abnormal decrease in nucleation rates below the cross-over temperature is most likely because, in this regime, the CRR size controls the critical nucleus size and the nucleation rate. This finding links, for the first time, measured nucleation kinetics to the dynamic heterogeneities in a supercooled liquid. [ABSTRACT FROM AUTHOR]

Published
2016
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48. Viscosity of silica and doped silica melts: evidence for a crossover temperature.

Author

Mauro, John C., Kurkjian, Charles R., Gupta, Prabhat K., and Kob, Walter

Subjects
GLASS transition temperature, VISCOSITY, VISCOUS flow, SILICA, ACTIVATION energy
Abstract

Silica is known as the archetypal strong liquid, exhibiting an Arrhenius viscosity curve with a high glass transition temperature and constant activation energy. However, given the ideally isostatic nature of the silica network, the presence of even a small concentration of defects can lead to a significant decrease in both the glass transition temperature and activation energy for viscous flow. To understand the impact of trace level dopants on the viscosity of silica, we measure the viscosity‐temperature curves for seven silica glass samples having different impurities, including four natural and three synthetic samples. Depending on the type of dopant, the glass transition temperature can vary by nearly 300 K. A common crossover is found for all viscosity curves around ~2200–2500 K, which we attribute to a change of the transport mechanism in the melt from being dominated by intrinsic defects at high temperature to dopant‐induced defects at low temperatures. [ABSTRACT FROM AUTHOR]

Published
2022
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49. Environmental Monitoring Network for India

Author

Sundareshwar, P. V., Murtugudde, R., Srinivasan, G., Singh, S., Ramesh, K. J., Ramesh, R., Verma, S. B., Agarwal, D., Baldocchi, D., Baru, C. K., Baruah, K. K., Chowdhury, G. R., Dadhwal, V. K., Dutt, C. B. S., Fuentes, J., Gupta, Prabhat K., Hargrove, W. W., Howard, M., Jha, C. S., Lal, S., Michener, W. K., Mitra, A. P., Morris, J. T., Myneni, R. R., Naja, M., Nemani, R., Purvaja, R., Raha, S., Santhana Vanan, S. K., Sharma, M., Subramaniam, A., Sukumar, R., Twilley, R. R., and Zimmerman, P. R.

Published
2007
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