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Vikas Tomar - One of the best experts on this subject based on the ideXlab platform.

  • The effect of tensile and compressive loading on the hierarchical strength of idealized tropocollagen–hydroxyapatite biomaterials as a function of the Chemical Environment
    Journal of physics. Condensed matter : an Institute of Physics journal, 2009
    Co-Authors: Devendra K. Dubey, Vikas Tomar
    Abstract:

    Hard biomaterials such as bone, dentin and nacre have primarily a polypeptide phase (e.g. tropocollagen (TC)) and a mineral phase (e.g. hydroxyapatite (HAP) or aragonite) arranged in a staggered manner. It has been observed that the mechanical behaviour of such materials changes with the Chemical Environment and the direction of applied loading. In the presented investigation, explicit three-dimensional molecular dynamics (MD) simulations based analyses are performed on idealized TC–HAP composite biomaterial systems to understand the effects of tensile and compressive loadings in three different Chemical Environments: (1) unsolvated, (2) solvated with water and (3) calcinated and solvated with water. The MD analyses are performed on two interfacial supercells corresponding to the lowest structural level (level n) of TC–HAP interactions and on two other supercells with HAP supercells arranged in a staggered manner (level n+1) in a TC matrix. The supercells at level n+1 are formed by arranging level n interfacial supercells in a staggered manner. Analyses show that at level n, the presence of water molecules results in greater stability of TC molecules and TC–HAP interfaces during mechanical deformation. In addition, water also acts as a lubricant between adjacent TC molecules. Under the application of shear stress dominated loading, water molecules act to strengthen the TC–HAP interfacial strength in a manner similar to the action of glue. An overall effect of the observed mechanisms is that, in a staggered arrangement, tensile strength increases in the presence of water and calcinated water Environments. On the other hand, corresponding compressive strength decreases under similar circumstances. Fundamentally, supercells with primarily normal load transfer at the TC–HAP interfaces are stronger in tensile shear loading. On the other hand, supercells with primarily tangential or shear load transfer at the TC–HAP interfaces are stronger in compressive shear loading. A combination of changes in Chemical Environment from vacuum to calcinated water and changes in interfacial configurations in a staggered arrangement could be chosen to make the TC–HAP material stronger under applied deformation.

  • the effect of tensile and compressive loading on the hierarchical strength of idealized tropocollagen hydroxyapatite biomaterials as a function of the Chemical Environment
    Journal of Physics: Condensed Matter, 2009
    Co-Authors: Devendra K. Dubey, Vikas Tomar
    Abstract:

    Hard biomaterials such as bone, dentin and nacre have primarily a polypeptide phase (e.g. tropocollagen (TC)) and a mineral phase (e.g. hydroxyapatite (HAP) or aragonite) arranged in a staggered manner. It has been observed that the mechanical behaviour of such materials changes with the Chemical Environment and the direction of applied loading. In the presented investigation, explicit three-dimensional molecular dynamics (MD) simulations based analyses are performed on idealized TC–HAP composite biomaterial systems to understand the effects of tensile and compressive loadings in three different Chemical Environments: (1) unsolvated, (2) solvated with water and (3) calcinated and solvated with water. The MD analyses are performed on two interfacial supercells corresponding to the lowest structural level (level n) of TC–HAP interactions and on two other supercells with HAP supercells arranged in a staggered manner (level n+1) in a TC matrix. The supercells at level n+1 are formed by arranging level n interfacial supercells in a staggered manner. Analyses show that at level n, the presence of water molecules results in greater stability of TC molecules and TC–HAP interfaces during mechanical deformation. In addition, water also acts as a lubricant between adjacent TC molecules. Under the application of shear stress dominated loading, water molecules act to strengthen the TC–HAP interfacial strength in a manner similar to the action of glue. An overall effect of the observed mechanisms is that, in a staggered arrangement, tensile strength increases in the presence of water and calcinated water Environments. On the other hand, corresponding compressive strength decreases under similar circumstances. Fundamentally, supercells with primarily normal load transfer at the TC–HAP interfaces are stronger in tensile shear loading. On the other hand, supercells with primarily tangential or shear load transfer at the TC–HAP interfaces are stronger in compressive shear loading. A combination of changes in Chemical Environment from vacuum to calcinated water and changes in interfacial configurations in a staggered arrangement could be chosen to make the TC–HAP material stronger under applied deformation.

  • Understanding the influence of structural hierarchy and its coupling with Chemical Environment on the strength of idealized tropocollagen–hydroxyapatite biomaterials
    Journal of the Mechanics and Physics of Solids, 2009
    Co-Authors: Devendra K. Dubey, Vikas Tomar
    Abstract:

    Abstract Hard biomaterials such as bone, dentin, and nacre have primarily an organic phase (e.g. tropocollagen (TC)) and a mineral phase (e.g. hydroxyapatite (HAP) or aragonite) arranged in a staggered arrangement at the nanoscopic length scale. Interfacial interactions between the organic phase and the mineral phase as well as the structural effects arising due to the staggered arrangement significantly affect the strength of such biomaterials. The effect of such factors is intricately intertwined with the Chemical Environment of such materials. In the present investigation, an idealized TC–HAP composite system under tensile loading is analyzed using explicit three-dimensional (3-D) molecular dynamics (MD) simulations to develop an understanding of these factors. The material system is analyzed in three different Environments: (1) in the absence of water molecules (non-hydrated), (2) in the presence of water molecules (hydrated), and (3) in the presence of water molecules with calcium ions (ionized water). The analyses focus on understanding the correlations among factors such as the structural arrangement, the peak stress during deformation, Young's modulus, the peak interfacial strength, and the length scale of the localization of peak stress during deformation. Analyses show that maximizing the contact area between the TC and HAP phases results in higher interfacial strength as well as higher fracture strength. Due to the staggered arrangement, the orientation of HAP crystals has insignificant effect on the biomaterial strength. Analyses based on strength scaling as a function of structural hierarchy level reveal that while peak strength follows a multiscaling relation, the fracture strength does not. The peak strain for failure was found to be independent of the changes in levels of structural hierarchy. Overall, the analyses, being limited in size due to the computational time constraint, point out important correlations between the mechanical strength and Chemically influenced structural hierarchy of biomaterials.

Zaide Deng - One of the best experts on this subject based on the ideXlab platform.

  • Influence of Chemical Environment on the optical properties in transition metal ions doped materials.
    Journal of fluorescence, 2006
    Co-Authors: Zaide Deng
    Abstract:

    The sensibility of luminescent properties in transition metal doped materials to the matrices' Chemical Environment is explained in this paper, this is because of their strong phonon-electron coupling which are caused by the 3d electrons exposed nature. The influence of the Chemical Environments on the Mn2+-doped materials' optical properties, including the structure type of coordinate polyhedron, the polyhedral bridge linking manner and the lattice parameter, was illustrated in detail in this work. The impact of crystal field strength parameter (10 Dq) on the maximum energy differentiae in spontaneous emission band of Cr3+:4T2g→4A2g and in excited state absorption band 4T2g→4T1g (4F), and covalent bond intension's impact on the optical properties of Os4+ were also analyzed. This work's purpose is to discover the principle of the sensibility character, then we can use it to optimal the design of materials in order to find the excellent luminescent materials for practical utilization.

Y. C. Jean - One of the best experts on this subject based on the ideXlab platform.

  • Study of the Chemical Environment inside Free Volume Holes in Halogenated Styrene Polymers Using Positron Annihilation Spectroscopy
    Macromolecules, 2012
    Co-Authors: Renwu Zhang, Jessica Robles, Jiwoong Kang, Hussein Samha, Hongmin Chen, Y. C. Jean
    Abstract:

    In this paper, a systematic study is provided of the Chemical Environment inside free volume holes in a series of halogenated polystyrenes (p-position), −[CH2CH C6H5X]n– (X = F, Cl, Br, I), by using positron annihilation spectroscopy. In such polymers it was determined that the Chemical Environment is the major effect on Doppler broadening of two 511 keV γ photons from positron–electron annihilation. Doppler broadening energy spectroscopy (DBES) and positron annihilation lifetime spectroscopy (PALS) were combined in a novel approach to study the Chemical Environment in a polymer system. A highly linear relationship between Doppler broadenings caused by electron kinetic energies of valence electrons and the ionization potentials of halogen elements was obtained, as well as a similar correlation with the results from ab initio molecular orbital (MO) calculations for monohalogenobenzenes, C6H5X (X = F, Cl, Br, I). The results demonstrate that the combination of DBES and PALS may provide an effective way to s...

  • Chemical Environment in halogenated styrene polymers studied by using positron annihilation lifetime spectroscopy
    Radiation Physics and Chemistry, 2003
    Co-Authors: Renwu Zhang, Hongmin Chen, Junjie Zhang, T. C. Sandreczki, Y. C. Jean
    Abstract:

    Abstract Polystyrene samples, incorporated with halogen elements (F, Cl, Br, I) on the para -position of the benzene ring, were studied using positron annihilation lifetime spectroscopy. It was found that the free-volume hole size is significantly affected by the internal Coulombic interaction of the halogen group, and is mainly related to the electronegativity of halogen–carbon bonds. In addition, it is found that the free-volume is secondarily modified by the steric effect of the side groups. The intensity of o -Ps has a linear relationship with the strength of the C–X bond and is strongly affected by the Chemical Environment in a halogenated styrene polymer system.

Devendra K. Dubey - One of the best experts on this subject based on the ideXlab platform.

  • The effect of tensile and compressive loading on the hierarchical strength of idealized tropocollagen–hydroxyapatite biomaterials as a function of the Chemical Environment
    Journal of physics. Condensed matter : an Institute of Physics journal, 2009
    Co-Authors: Devendra K. Dubey, Vikas Tomar
    Abstract:

    Hard biomaterials such as bone, dentin and nacre have primarily a polypeptide phase (e.g. tropocollagen (TC)) and a mineral phase (e.g. hydroxyapatite (HAP) or aragonite) arranged in a staggered manner. It has been observed that the mechanical behaviour of such materials changes with the Chemical Environment and the direction of applied loading. In the presented investigation, explicit three-dimensional molecular dynamics (MD) simulations based analyses are performed on idealized TC–HAP composite biomaterial systems to understand the effects of tensile and compressive loadings in three different Chemical Environments: (1) unsolvated, (2) solvated with water and (3) calcinated and solvated with water. The MD analyses are performed on two interfacial supercells corresponding to the lowest structural level (level n) of TC–HAP interactions and on two other supercells with HAP supercells arranged in a staggered manner (level n+1) in a TC matrix. The supercells at level n+1 are formed by arranging level n interfacial supercells in a staggered manner. Analyses show that at level n, the presence of water molecules results in greater stability of TC molecules and TC–HAP interfaces during mechanical deformation. In addition, water also acts as a lubricant between adjacent TC molecules. Under the application of shear stress dominated loading, water molecules act to strengthen the TC–HAP interfacial strength in a manner similar to the action of glue. An overall effect of the observed mechanisms is that, in a staggered arrangement, tensile strength increases in the presence of water and calcinated water Environments. On the other hand, corresponding compressive strength decreases under similar circumstances. Fundamentally, supercells with primarily normal load transfer at the TC–HAP interfaces are stronger in tensile shear loading. On the other hand, supercells with primarily tangential or shear load transfer at the TC–HAP interfaces are stronger in compressive shear loading. A combination of changes in Chemical Environment from vacuum to calcinated water and changes in interfacial configurations in a staggered arrangement could be chosen to make the TC–HAP material stronger under applied deformation.

  • the effect of tensile and compressive loading on the hierarchical strength of idealized tropocollagen hydroxyapatite biomaterials as a function of the Chemical Environment
    Journal of Physics: Condensed Matter, 2009
    Co-Authors: Devendra K. Dubey, Vikas Tomar
    Abstract:

    Hard biomaterials such as bone, dentin and nacre have primarily a polypeptide phase (e.g. tropocollagen (TC)) and a mineral phase (e.g. hydroxyapatite (HAP) or aragonite) arranged in a staggered manner. It has been observed that the mechanical behaviour of such materials changes with the Chemical Environment and the direction of applied loading. In the presented investigation, explicit three-dimensional molecular dynamics (MD) simulations based analyses are performed on idealized TC–HAP composite biomaterial systems to understand the effects of tensile and compressive loadings in three different Chemical Environments: (1) unsolvated, (2) solvated with water and (3) calcinated and solvated with water. The MD analyses are performed on two interfacial supercells corresponding to the lowest structural level (level n) of TC–HAP interactions and on two other supercells with HAP supercells arranged in a staggered manner (level n+1) in a TC matrix. The supercells at level n+1 are formed by arranging level n interfacial supercells in a staggered manner. Analyses show that at level n, the presence of water molecules results in greater stability of TC molecules and TC–HAP interfaces during mechanical deformation. In addition, water also acts as a lubricant between adjacent TC molecules. Under the application of shear stress dominated loading, water molecules act to strengthen the TC–HAP interfacial strength in a manner similar to the action of glue. An overall effect of the observed mechanisms is that, in a staggered arrangement, tensile strength increases in the presence of water and calcinated water Environments. On the other hand, corresponding compressive strength decreases under similar circumstances. Fundamentally, supercells with primarily normal load transfer at the TC–HAP interfaces are stronger in tensile shear loading. On the other hand, supercells with primarily tangential or shear load transfer at the TC–HAP interfaces are stronger in compressive shear loading. A combination of changes in Chemical Environment from vacuum to calcinated water and changes in interfacial configurations in a staggered arrangement could be chosen to make the TC–HAP material stronger under applied deformation.

  • Understanding the influence of structural hierarchy and its coupling with Chemical Environment on the strength of idealized tropocollagen–hydroxyapatite biomaterials
    Journal of the Mechanics and Physics of Solids, 2009
    Co-Authors: Devendra K. Dubey, Vikas Tomar
    Abstract:

    Abstract Hard biomaterials such as bone, dentin, and nacre have primarily an organic phase (e.g. tropocollagen (TC)) and a mineral phase (e.g. hydroxyapatite (HAP) or aragonite) arranged in a staggered arrangement at the nanoscopic length scale. Interfacial interactions between the organic phase and the mineral phase as well as the structural effects arising due to the staggered arrangement significantly affect the strength of such biomaterials. The effect of such factors is intricately intertwined with the Chemical Environment of such materials. In the present investigation, an idealized TC–HAP composite system under tensile loading is analyzed using explicit three-dimensional (3-D) molecular dynamics (MD) simulations to develop an understanding of these factors. The material system is analyzed in three different Environments: (1) in the absence of water molecules (non-hydrated), (2) in the presence of water molecules (hydrated), and (3) in the presence of water molecules with calcium ions (ionized water). The analyses focus on understanding the correlations among factors such as the structural arrangement, the peak stress during deformation, Young's modulus, the peak interfacial strength, and the length scale of the localization of peak stress during deformation. Analyses show that maximizing the contact area between the TC and HAP phases results in higher interfacial strength as well as higher fracture strength. Due to the staggered arrangement, the orientation of HAP crystals has insignificant effect on the biomaterial strength. Analyses based on strength scaling as a function of structural hierarchy level reveal that while peak strength follows a multiscaling relation, the fracture strength does not. The peak strain for failure was found to be independent of the changes in levels of structural hierarchy. Overall, the analyses, being limited in size due to the computational time constraint, point out important correlations between the mechanical strength and Chemically influenced structural hierarchy of biomaterials.

Yu Nishihara - One of the best experts on this subject based on the ideXlab platform.

  • effect of Chemical Environment on the hydrogen related defect chemistry in wadsleyite
    American Mineralogist, 2008
    Co-Authors: Yu Nishihara, Toru Shinmei, Shun Ichiro Karato
    Abstract:

    The effect of Chemical Environment on the hydrogen-related defect chemistry in wadsleyite was investigated using Fourier-transform infrared (FTIR) spectroscopy. Samples were annealed at P = 14–16 GPa and T = 1230–1973 K using Kawai-type multi-anvil apparatus. The effect of oxygen fugacity ( f O 2 ) was investigated using three metal-oxide buffers (Mo-MoO 2 , Ni-NiO, and Re-ReO 2 ). The effect of water fugacity ( f H 2 O ) was studied using two different capsule assemblies (“nominally dry” and “dry” assemblies). A range of total OH concentration ( C OH,Total ) of studied wadslyeites varies between 6 Si ( 2 O) and 23 000 H/106Si (1400 wt ppm H 2 O). The observed FTIR spectra were classified into four different classes, i.e., peaks at 3620 (“3620”), 3480 (“3480”), and 3205 cm −1 (“3205”) and the others (Group O), where the Group O includes peaks at 3270, 3330, and 3580 cm −1 . The variation in OH concentration corresponding to each peak was analyzed separately. The OH concentrations correspond to “3620,” “3480,” and “3205” were found to be highly dependent on both f H 2 O and f O 2 . Assuming C OH,Group O = 2[(2H) M x ] ( C OH,Group O is OH concentration of Group O), present data were analyzed by using thermodynamic model for concentration of hydrogen-related defects. Based on analytical results, OH concentration of “3620” and “3480” was found to be reasonably explained by q = 1/2 and r = 1/12 ( q and r are f H 2 O and f O 2 exponents, respectively), whereas that of “3205” was consistent with q = 1/2 and r = −1/12. These results suggest that “3620” and “3480” correspond to H M ′ whereas “3205” corresponds to H•, respectively, under the charge neutrality condition of [Fe M ′] = 2[V M ″].

  • grain growth kinetics in wadsleyite effects of Chemical Environment
    Physics of the Earth and Planetary Interiors, 2006
    Co-Authors: Yu Nishihara, Toru Shinmei, Shun Ichiro Karato
    Abstract:

    Abstract Grain-growth kinetics in wadsleyite was investigated using a multianvil high-pressure apparatus. Fine-grained wadsleyite aggregates were synthesized by isostatic hot-pressing and were subsequently annealed under high pressure and temperature in a controlled Chemical Environment. Wadsleyite samples show normal grain-growth characterized by a log-normal grain-size distribution following the relation, L n − L 0 n = k t where n is a constant, L the grain-size at time t, L0 the grain-size at time t = 0 and k is a rate constant that depends on temperature T and Chemical Environments ( f O 2 : oxygen fugacity in Pa, COH: water content in H/106Si) as: k = A ′ D f O 2 r D exp − H D ′ * R T + A ′ W f O 2 r W C OH q exp − H W ′ * R T with A ′ D = 10 − 4.9 ± 6.1 ( − 8.0 ± 7.4 ) ( m n s − 1 P a − r D ) , rD = 0.12 ± 0.11(0.20 ± 0.14), H D ′ *  = 410 ± 230(500 ± 270) kJ/mol, A ′ W = 10 − 18.2 ± 1.4 ( − 24.0 ± 1.7 ) ( m n s − 1 P a − r W ) , rW = 0.14 ± 0.05(0.22 ± 0.06), q = 1.7 ± 0.3(2.2 ± 0.3) and H W ′ *  = 120 ± 60(160 ± 70) kJ/mol with assumed value of n = 2(3) (values in parentheses denote parameters for n = 3). Both water and oxygen fugacities significantly enhance grain-growth kinetics. The large value of the parameter describing the water fugacity dependence, q ∼ 1.5–2.5, cannot be explained solely by a simple model in which grain-growth is controlled by diffusion of atoms (defects) across the grain-boundaries The interaction of grain-boundaries with charged defects or the density of hydrated ledges may be important factors that control the grain-growth kinetics of wadsleyite. When compared at similar thermo-Chemical conditions, grain-growth of wadsleyite is found to be more sluggish than grain-growth of olivine. The present results show that a small wadsleyite grain-size ( 100,000 H/106Si) is present, a small grain-size (