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Vlad Sadtchenko - One of the best experts on this subject based on the ideXlab platform.
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enthalpy and high temperature relaxation kinetics of stable vapor deposited glasses of toluene
Journal of Chemical Physics, 2014Co-Authors: Deepanjan Bhattacharya, Vlad SadtchenkoAbstract:Stable non-crystalline toluene films of micrometer and nanometer thicknesses were grown by vapor deposition at distinct rates and probed by fast scanning calorimetry. Fast scanning calorimetry is shown to be extremely sensitive to the structure of the vapor-deposited phase and was used to characterize simultaneously its kinetic stability and its thermodynamic properties. According to our analysis, transformation of vapor-deposited samples of toluene during heating with rates in excess 105 K s−1 follows the zero-order kinetics. The transformation rate correlates strongly with the initial enthalpy of the sample, which increases with the deposition rate according to sub-Linear Law. Analysis of the transformation kinetics of vapor-deposited toluene films of various thicknesses reveal a sudden increase in the transformation rate for films thinner than 250 nm. The change in kinetics seems to correlate with the surface roughness scale of the substrate. The implications of these findings for the formation mechanism and structure of vapor-deposited stable glasses are discussed.
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enthalpy and high temperature relaxation kinetics of stable vapor deposited glasses of toluene
arXiv: Soft Condensed Matter, 2014Co-Authors: Deepanjan Bhattacharya, Vlad SadtchenkoAbstract:Stable non-crystalline toluene films of micrometer and nanometer thicknesses were grown by vapor deposition at distinct rates and probed by Fast Scanning Calorimetry. Fast scanning calorimetry is shown to be extremely sensitive to the structure of the vapor-deposited phase and was used to characterize simultaneously its kinetic stability and its thermodynamic properties. According to our analysis, transformation of vapor -deposited samples of toluene during heating with rates in excess 10^5 K/s follows the zero-order kinetics. The transformation rate correlates strongly with the initial enthalpy of the sample, which increases with the deposition rate according to sub-Linear Law. Analysis of the transformation kinetics of vapor deposited toluene films of various thicknesses reveal a sudden increase in the transformation rate for films thinner than 250 nm. The change in kinetics correlates with the surface roughness scale of the substrate, which is interpreted as evidence for kinetic anisotropy of the samples. The implications of these findings for the formation mechanism and structure of vapor deposited stable glasses are discussed.
Jeanpaul Balayssac - One of the best experts on this subject based on the ideXlab platform.
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combination of the wenner resistivimeter and torrent permeameter methods for assessing carbonation depth and saturation level of concrete
Construction and Building Materials, 2018Co-Authors: Stephanie Bonnet, Jeanpaul BalayssacAbstract:Abstract Assessing carbonation depth is of great interest for the diagnosis of reinforced concrete structures because carbonation is one of the origins of steel corrosion. The assessment of carbonation depth is usually performed by a simple and reliable semi-destructive test consisting in spraying a colored indicator on a sample extracted from the structure. When the structure is large, this test must be reproduced many times if an assessment of the variability of carbonation depth is required. In this case, the extraction of multiple samples can be prohibitive from the technical and economic points of view. So, in this case, a non-destructive testing (NDT) method could be relevant. However, even when NDT methods can be used, there is a need to improve the interpretation of their results. In this study, the use of two usual NDT methods is proposed: resistivity measurement by a Wenner probe and surface permeability assessment by a Torrent permeameter. Both techniques are implemented on carbonated slabs having different carbonated depths and at different saturation degrees. The results show that the two techniques are sensitive to moisture and carbonation. For a given saturation level, resistivity increases when the carbonated depth increases and resistivity decreases when the saturation level increases. Torrent permeability decreases when the saturation degree and carbonated depth increase. Good repeatability is observed for resistivity measurements while a larger scatter is obtained for Torrent permeability. Empirical Laws are built for the relationships between resistivity or permeability and saturation degree and carbonated depth. For resistivity, either a Linear model between resistivity and saturation degree is used or Archie’s Law is adapted to take the effect of carbonation into account. Following the same idea, a Linear Law between Torrent permeability and saturation degree is adapted to the effect of carbonation. Because resistivity can be measured only if the saturation degree is rather high, i.e. if there is a continuity of the interstitial solution, and because permeability assessment is impossible if the concrete is fully saturated, these Laws are limited to saturation degrees in the 40–83% range. Then, these Laws are used to predict carbonation depth and saturation degree on a wall designed with the same concrete but stored in different conditions. The results show that resistivity and Torrent permeability can be used for the combined assessment of carbonation depth and saturation degree in laboratory conditions.
L. Briottet - One of the best experts on this subject based on the ideXlab platform.
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damage in a viscoplastic material part ii overall behaviour
International Journal of Plasticity, 1998Co-Authors: L. BriottetAbstract:Abstract The overall behaviour of a damaged viscoplastic material under axisymmetric loading is addressed in this paper. A Linear viscous matrix containing aligned spheroidal cavities is first considered. Its overall behaviour is estimated by means of a differential scheme. The damage-induced morphological anisotropy, due to the shape of the voids, is then analyzed. It is shown to be significant even at low volume fractions of cavities ( ƒ ), when the latter are prolate or oblate. These results are then used to predict the behaviour of a nonLinear viscous matrix containing aligned spheroidal cavities, by means of a variational principle proposed by Ponte Castaneda (1991). Two types of nonLinear matrix behaviour are considered: a power Law corresponding to metal forming at moderate strain rates and a Linear Law with nonzero intercept suited to high strain rates.The constitutive equations of such nonLinear damaged materials have been used in a companion paper in order to study the influence of matrix compressibility on the growth of a spheroidal cavity during straining.
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damage in a viscoplastic material part i cavity growth
International Journal of Plasticity, 1996Co-Authors: L. Briottet, Helmut Klocker, F MontheilletAbstract:Abstract The exact velocity, stress and strain rate fields around a spheroidal cavity in an infinite Linear viscoplastic compressible matrix are derived analytically by the ‘three function approach’. The perturbation of the velocity field due to the cavity is the superposition of three independent modes, inducing homothetic growth, pure distortion and both volume and shape changes, respectively. This solution is then used to investigate the velocity field around a spheroidal cavity in a nonLinear viscous compressible material by means of a variational principle. The behaviour of such damaged Linear and nonLinear materials will be discussed in a forthcoming companion paper. The importance of the reference strain, while studying void growth in a compressible material, is emphasized. If the axial strain is chosen as a reference, void growth is found to be enhanced at low triaxiality ratios, but lowered at high triaxiality ratios in a compressible matrix relative to an incompressible one. Finally, the transition from a power Law to a Linear Law with intercept, at increasing strain rates, is shown to reduce damage growth rate.
Lingen Chen - One of the best experts on this subject based on the ideXlab platform.
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entropy generation minimization for isothermal crystallization processes with a generalized mass diffusion Law
International Journal of Heat and Mass Transfer, 2018Co-Authors: Lingen ChenAbstract:Abstract Entropy generation minimization for a class of isothermal crystallization processes with a generalized mass diffusion Law is investigated in this paper. For the given total mass of crystals, the optimality condition corresponding to the MEG (Minimum Entropy Generation) of the process is obtained firstly, and special cases for both the Linear [ g ∝ Δ ( μ ) ] and the diffusive [ g ∝ Δ ( c ) ] mass diffusion Laws are further derived. The optimization results are also compared with the two different mass diffusion strategies of CKCC (Constant Key Component Concentration) and CMDF (Constant Mass Diffusion Flux) operations. The results indicate that for the case with the Linear Law, the entropy generation rate for the MEG of the process keeps constant, and the total entropy generations for the strategies of CKCC and CMDF operations are equal to each other; while for the case with the diffusive Law, the entropy generation rate for the MEG of the process decreases with the time, and the strategy of CMDF is superior to that of CKCC. The results can provide important guidelines for optimal design and operation of the crystallization processes in engineering.
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maximum work output of multistage continuous carnot heat engine system with finite reservoirs of thermal capacity and radiation between heat source and working fluid
Thermal Science, 2010Co-Authors: Lingen Chen, Fengrui SunAbstract:Optimal temperature profile for maximum work output of multistage continuous Carnot heat engine system with two reservoirs of finite thermal capacity is determined. The heat transfer between heat source and the working fluid obeys radiation Law and the heat transfer between heat sink and the working fluid obeys Linear Law. The solution is obtained by using optimal control theory and pseudo-Newtonian heat transfer model. It is shown that the temperature of driven fluid monotonically decreases with respect to flow velocity and process duration. The maximum work is obtained. The obtained results are compared with those obtained with infinite low temperature heat sink.
Deepanjan Bhattacharya - One of the best experts on this subject based on the ideXlab platform.
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enthalpy and high temperature relaxation kinetics of stable vapor deposited glasses of toluene
Journal of Chemical Physics, 2014Co-Authors: Deepanjan Bhattacharya, Vlad SadtchenkoAbstract:Stable non-crystalline toluene films of micrometer and nanometer thicknesses were grown by vapor deposition at distinct rates and probed by fast scanning calorimetry. Fast scanning calorimetry is shown to be extremely sensitive to the structure of the vapor-deposited phase and was used to characterize simultaneously its kinetic stability and its thermodynamic properties. According to our analysis, transformation of vapor-deposited samples of toluene during heating with rates in excess 105 K s−1 follows the zero-order kinetics. The transformation rate correlates strongly with the initial enthalpy of the sample, which increases with the deposition rate according to sub-Linear Law. Analysis of the transformation kinetics of vapor-deposited toluene films of various thicknesses reveal a sudden increase in the transformation rate for films thinner than 250 nm. The change in kinetics seems to correlate with the surface roughness scale of the substrate. The implications of these findings for the formation mechanism and structure of vapor-deposited stable glasses are discussed.
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enthalpy and high temperature relaxation kinetics of stable vapor deposited glasses of toluene
arXiv: Soft Condensed Matter, 2014Co-Authors: Deepanjan Bhattacharya, Vlad SadtchenkoAbstract:Stable non-crystalline toluene films of micrometer and nanometer thicknesses were grown by vapor deposition at distinct rates and probed by Fast Scanning Calorimetry. Fast scanning calorimetry is shown to be extremely sensitive to the structure of the vapor-deposited phase and was used to characterize simultaneously its kinetic stability and its thermodynamic properties. According to our analysis, transformation of vapor -deposited samples of toluene during heating with rates in excess 10^5 K/s follows the zero-order kinetics. The transformation rate correlates strongly with the initial enthalpy of the sample, which increases with the deposition rate according to sub-Linear Law. Analysis of the transformation kinetics of vapor deposited toluene films of various thicknesses reveal a sudden increase in the transformation rate for films thinner than 250 nm. The change in kinetics correlates with the surface roughness scale of the substrate, which is interpreted as evidence for kinetic anisotropy of the samples. The implications of these findings for the formation mechanism and structure of vapor deposited stable glasses are discussed.