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M. C. Valsakumar - One of the best experts on this subject based on the ideXlab platform.
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Assessment of the mechanical properties of monolayer graphene using the energy and strain-Fluctuation Methods
RSC Advances, 2018Co-Authors: Siby Thomas, K M Ajith, Sang Uck Lee, M. C. ValsakumarAbstract:Molecular statics and dynamics simulations were performed to investigate the mechanical properties of a monolayer graphene sheet using an efficient energy Method and strain-Fluctuation Method. Using the energy Method, we observed that the mechanical properties of an infinite graphene sheet are isotropic, whereas for a finite sheet, they are anisotropic. This work is the first to report the temperature-dependent elastic constants of graphene between 100 and 1000 K using the strain-Fluctuation Method. We found that the out-of-plane thermal excursions in a graphene membrane lead to strong anharmonic behavior, which allows large deviations from isotropic elasticity. The computed Young's modulus and Poisson's ratio of a sheet with an infinite spatial extent are 0.939 TPa and 0.223, respectively. We also found that graphene sheets with both finite and infinite spatial extent satisfy the Born elastic stability conditions. We extracted the variation in bending modulus with the system size at zero kelvin (0.83 eV) using a formula derived from the Foppl–von Karman approach. When the temperature increases, the Young's modulus of the sample decreases, which effectively reduces the longitudinal and shear wave velocities.
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Effect of ripples on the finite temperature elastic properties of hexagonal boron nitride using strain-Fluctuation Method
Superlattices and Microstructures, 2017Co-Authors: Siby Thomas, K M Ajith, M. C. ValsakumarAbstract:Abstract This work intents to put forth the results of a classical molecular dynamics study to investigate the temperature dependent elastic constants of monolayer hexagonal boron nitride (h-BN) between 100 and 1000 K for the first time using strain Fluctuation Method. The temperature dependence of out-of-plane Fluctuations (ripples) is quantified and is explained using continuum theory of membranes. At low temperatures, negative in-plane thermal expansion is observed and at high temperatures, a transition to positive thermal expansion has been observed due to the presence of thermally excited ripples. The decrease of Young's modulus, bulk modulus, shear modulus and Poisson's ratio with increase in temperature has been analyzed. The thermal rippling in h-BN leads to strong anharmonic behaviour that causes large deviation from the isotropic elasticity. A detailed study shows that the strong thermal rippling in large systems is also responsible for the softening of elastic constants in h-BN. From the determined values of elastic constants and elastic moduli, it has been elucidated that 2D h-BN sheets meet the Born's mechanical stability criterion in the investigated temperature range. The variation of longitudinal and shear velocities with temperature is also calculated from the computed values of elastic constants and elastic moduli.
Siby Thomas - One of the best experts on this subject based on the ideXlab platform.
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Assessment of the mechanical properties of monolayer graphene using the energy and strain-Fluctuation Methods
RSC Advances, 2018Co-Authors: Siby Thomas, K M Ajith, Sang Uck Lee, M. C. ValsakumarAbstract:Molecular statics and dynamics simulations were performed to investigate the mechanical properties of a monolayer graphene sheet using an efficient energy Method and strain-Fluctuation Method. Using the energy Method, we observed that the mechanical properties of an infinite graphene sheet are isotropic, whereas for a finite sheet, they are anisotropic. This work is the first to report the temperature-dependent elastic constants of graphene between 100 and 1000 K using the strain-Fluctuation Method. We found that the out-of-plane thermal excursions in a graphene membrane lead to strong anharmonic behavior, which allows large deviations from isotropic elasticity. The computed Young's modulus and Poisson's ratio of a sheet with an infinite spatial extent are 0.939 TPa and 0.223, respectively. We also found that graphene sheets with both finite and infinite spatial extent satisfy the Born elastic stability conditions. We extracted the variation in bending modulus with the system size at zero kelvin (0.83 eV) using a formula derived from the Foppl–von Karman approach. When the temperature increases, the Young's modulus of the sample decreases, which effectively reduces the longitudinal and shear wave velocities.
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Effect of ripples on the finite temperature elastic properties of hexagonal boron nitride using strain-Fluctuation Method
Superlattices and Microstructures, 2017Co-Authors: Siby Thomas, K M Ajith, M. C. ValsakumarAbstract:Abstract This work intents to put forth the results of a classical molecular dynamics study to investigate the temperature dependent elastic constants of monolayer hexagonal boron nitride (h-BN) between 100 and 1000 K for the first time using strain Fluctuation Method. The temperature dependence of out-of-plane Fluctuations (ripples) is quantified and is explained using continuum theory of membranes. At low temperatures, negative in-plane thermal expansion is observed and at high temperatures, a transition to positive thermal expansion has been observed due to the presence of thermally excited ripples. The decrease of Young's modulus, bulk modulus, shear modulus and Poisson's ratio with increase in temperature has been analyzed. The thermal rippling in h-BN leads to strong anharmonic behaviour that causes large deviation from the isotropic elasticity. A detailed study shows that the strong thermal rippling in large systems is also responsible for the softening of elastic constants in h-BN. From the determined values of elastic constants and elastic moduli, it has been elucidated that 2D h-BN sheets meet the Born's mechanical stability criterion in the investigated temperature range. The variation of longitudinal and shear velocities with temperature is also calculated from the computed values of elastic constants and elastic moduli.
Sebastián Dietrich - One of the best experts on this subject based on the ideXlab platform.
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Application of the water table Fluctuation Method to characterize groundwater recharge in the Pampa plain, Argentina
Hydrological Sciences Journal, 2013Co-Authors: Marcelo Varni, Rocío Comas, Pablo Ariel Weinzettel, Sebastián DietrichAbstract:AbstractThe water table Fluctuation (WTF) Method is based on accepting that rises of a water table are due to recharge water reaching the groundwater. To apply the Method, an estimate of the specific yield of the zone of Fluctuation of the groundwater level is required. In this paper, a Method for estimation of the specific yield (Sy) is proposed; it consists of a graphical procedure which relates rises in groundwater level to the precipitation from which they originated. The Method presents more reliable Sy values as the number of events measured increases. Eighteen years of daily measurements were analysed to obtain a Sy value of 0.09, which was used to apply the WTF Method. The obtained recharge values show consistency with values calculated by other authors for the same region.Editor D. KoutsoyiannisCitation Varni, M., Comas, R., Weinzettel, P., and Dietrich, S., 2013. Application of water table Fluctuation Method to characterize the groundwater recharge in the Pampa plain, Argentina. Hydrological Sci...
K M Ajith - One of the best experts on this subject based on the ideXlab platform.
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Assessment of the mechanical properties of monolayer graphene using the energy and strain-Fluctuation Methods
RSC Advances, 2018Co-Authors: Siby Thomas, K M Ajith, Sang Uck Lee, M. C. ValsakumarAbstract:Molecular statics and dynamics simulations were performed to investigate the mechanical properties of a monolayer graphene sheet using an efficient energy Method and strain-Fluctuation Method. Using the energy Method, we observed that the mechanical properties of an infinite graphene sheet are isotropic, whereas for a finite sheet, they are anisotropic. This work is the first to report the temperature-dependent elastic constants of graphene between 100 and 1000 K using the strain-Fluctuation Method. We found that the out-of-plane thermal excursions in a graphene membrane lead to strong anharmonic behavior, which allows large deviations from isotropic elasticity. The computed Young's modulus and Poisson's ratio of a sheet with an infinite spatial extent are 0.939 TPa and 0.223, respectively. We also found that graphene sheets with both finite and infinite spatial extent satisfy the Born elastic stability conditions. We extracted the variation in bending modulus with the system size at zero kelvin (0.83 eV) using a formula derived from the Foppl–von Karman approach. When the temperature increases, the Young's modulus of the sample decreases, which effectively reduces the longitudinal and shear wave velocities.
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Effect of ripples on the finite temperature elastic properties of hexagonal boron nitride using strain-Fluctuation Method
Superlattices and Microstructures, 2017Co-Authors: Siby Thomas, K M Ajith, M. C. ValsakumarAbstract:Abstract This work intents to put forth the results of a classical molecular dynamics study to investigate the temperature dependent elastic constants of monolayer hexagonal boron nitride (h-BN) between 100 and 1000 K for the first time using strain Fluctuation Method. The temperature dependence of out-of-plane Fluctuations (ripples) is quantified and is explained using continuum theory of membranes. At low temperatures, negative in-plane thermal expansion is observed and at high temperatures, a transition to positive thermal expansion has been observed due to the presence of thermally excited ripples. The decrease of Young's modulus, bulk modulus, shear modulus and Poisson's ratio with increase in temperature has been analyzed. The thermal rippling in h-BN leads to strong anharmonic behaviour that causes large deviation from the isotropic elasticity. A detailed study shows that the strong thermal rippling in large systems is also responsible for the softening of elastic constants in h-BN. From the determined values of elastic constants and elastic moduli, it has been elucidated that 2D h-BN sheets meet the Born's mechanical stability criterion in the investigated temperature range. The variation of longitudinal and shear velocities with temperature is also calculated from the computed values of elastic constants and elastic moduli.
Michelle Garneau - One of the best experts on this subject based on the ideXlab platform.
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Quantification of peatland water storage capacity using the water table Fluctuation Method
Hydrological Processes, 2017Co-Authors: Marc-andré Bourgault, Marie Larocque, Michelle GarneauAbstract:Peat specific yield (Sy) is an important parameter involved in many peatland hydrological functions such as flood attenuation, baseflow contribution to rivers, and maintaining groundwater levels in surficial aquifers. However, general knowledge on peatland water storage capacity is still very limited, due in part to the technical difficulties related to in situ measurements. The objectives of this study were to quantify vertical Sy variations of water tables in peatlands using the water table Fluctuation (WTF) Method and to better understand the factors controlling peatland water storage capacity. The Method was tested in five ombrotrophic peatlands located in the St. Lawrence Lowlands (southern Quebec, Canada). In each peatland, water table wells were installed at three locations (up-gradient, mid-gradient, and down-gradient). Near each well, a 1-m long peat core (8 cm × 8 cm) was sampled, and subsamples were used to determine SY with standard gravitational drainage Method. A larger peat sample (25 cm × 60 cm × 40 cm) was also collected in one peatland to estimate Sy using a laboratory drainage Method. In all sites, the mean water table depth ranged from 9 to 49 cm below the peat surface, with annual Fluctuations varying between 15 and 29 cm for all locations. The WTF Method produced similar results to the gravitational drainage experiments, with values ranging between 0.13 and 0.99 for the WTF Method and between 0.01 and 0.95 for the gravitational drainage experiments. Sy was found to rapidly decrease with depth within 20 cm, independently of the within-site location and the mean annual water table depth. Dominant factors explaining Sy variations were identified using analysis of variance. The most important factor was peatland site, followed by peat depth and seasonality. Variations in storage capacity considering site and seasonality followed regional effective growing degree days and evapotranspiration patterns. This work provides new data on spatial variations of peatland water storage capacity using an easily implemented Method that requires only water table measurements and precipitation data.