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We propose a micromechanics model for aging basic creep of early-age concrete. Therefore, we formulate viscoelastic boundary value problems on two representative volume elements, one related to cement paste (composed of cement, water, hydrates, and air), and one related to concrete (composed of cement paste and aggregates). Homogenization of the 'nonaging' elastic and viscoelastic properties of the material's contituents involves the transformation of the aforementioned viscoelastic boundary value problems to the Laplace-Carson (LC) domain. There, formally elastic, classical self-consistent and Mori-Tanaka solutions are employed, leading to pointwisely defined LC-transformed tensorial creep and relaxation functions. Subsequently, the latter are back- transformed, by means of the Gaver-Wynn-Rho algorithm, into the time domain. Temporal derivatives of corresponding homogenized creep and relaxation tensors, evaluated for the current maturation state of the material (in terms of current volume fractions of cement, water, air, hydrates, and aggregates; being dependent on the hydration degree, as well as on the water-cement and aggregate-cement ratios) and for the current time period since loading of the hydrating composite material, allow for micromechanical prediction of the aging basic creep properties of early-age concrete. CE Database subject headings: Micromechanics; Viscoelasticity; Concrete; Creep.

The potential energy surfaces (PES) of Be–H2O and Be–NH3 are studied with particular attention to characterization of proton-donor properties of water and ammonia. Calculations were performed by means of both supermolecular and intermolecular Mo\ller Plesset perturbation theory. The Be–H2O PES reveals two van der Waals minima: the C2v minimum (De=176 cm-1, Re=6.5 bohr), and the H-bonded minimum (De=161 cm-1, Re=7.5 bohr), separated by a barrier of 43 cm-1 at the T-shaped configuration. The Be–NH3 PES reveals only one van der Waals minimum, at the C3v configuration (De=260 cm-1, Re=6.5 bohr) and a saddle point at the H-bonded geometry. The locations of the minima as well as the anisotropy of the interaction are determined by the anisotropy of electric polarization contribution, embodied by the self-consistent-field (SCF)-deformation and perturbation induction energies. [ABSTRACT FROM AUTHOR]

The perturbation theory of intermolecular forces in conjunction with the supermolecular Mo\ller–Plesset perturbation theory is applied to the analysis of the potential-energy surfaces of Kr–H2O and Kr–NH3 complexes. The valleylike minimum region on the potential-energy surface of Kr–H2O ranges from the coplanar geometry with the C2 axis of H2O nearly perpendicular to the O–Kr axis (T structure) to the H-bond structure in which Kr faces the H atom of H2O. Compared to the previously studied Ar–H2O [J. Chem. Phys. 94, 2807 (1991)] the minimum has more of the H-bond character. The minimum for Kr–NH3 corresponds to the T structure only, in accordance to the result for Ar–NH3 [J. Chem. Phys. 91, 7809 (1989)]. The minima in Kr–H2O and Kr–NH3 are roughly 27% and 19%, respectively, deeper than for the analogous Ar complexes. To examine the proton–donor abilities of O–H and N–H bonds the ratios of the deformation energy to dispersion energy are considered. They reflect fundamental differences between the two bonds and explain why NH3 is not capable of forming the H-bond structures to rare-gas atoms. [ABSTRACT FROM AUTHOR]

The combination of supermolecular Mo\ller–Plesset treatment with the perturbation theory of intermolecular forces is applied in the analysis of the potential-energy surface of Ar–H2O. The surface is very isotropic with the lowest barrier for rotation of ∼35 cm-1 above the absolute minimum. The lower bound for De is found to be 108 cm-1 and the complex reveals a very floppy structure, with Ar moving freely from the H-bridged structure to the coplanar and almost perpendicular arrangement of the C2 –water axis and the Ar–O axis, ‘‘T-shaped’’ structure. This motion is almost isoenergetic (energy change of less than 2 cm-1 ). The H-bridged structure is favored by the attractive induction and dispersion anisotropies; the T-shaped structure is favored by repulsive exchange anisotropy. The nonadditive effect in the Ar2–H2O cluster was also calculated. Implications of our results on the present models of hydrophobic interactions are also discussed. [ABSTRACT FROM AUTHOR]

Nonadditive contribution to the interaction energy in water trimer is analyzed in terms of Heitler–London exchange, SCF deformation, induction and dispersion nonadditivities. Nonadditivity originates mainly from the SCF deformation effect which is due to electric polarization. However, polarization does not serve as a universal mechanism for nonadditivity in water. In the double-donor configuration, for example, the Heitler–London exchange contribution is the most important and polarization yields the wrong sign. Correlation effects do not contribute significantly to the nonadditivity. A detailed analysis of the pair potential is also provided. The present two-body potential and its components are compared to the existing ab initio potentials (MCY) as well as to empirical ones (RWK2,TIP,SPC). The ways to improve these potentials are suggested. [ABSTRACT FROM AUTHOR]

This paper presents the first ab initio attempt to construct the stretching fundamentals νFX and νF...N (X=H, D, Li) in the FX...NH3 complexes taking into account the mechanical anharmonicity. A potential-energy surface V(rFX,RF...N) grid was generated at the self-consistent-field and second-order Mo\ller–Plesset levels. The coefficients fitting the potential-energy surface up to the fourth order have been used to compute the νFX and νF...N stretching modes. The vibrational problem is solved by means of a variational treatment which includes the effects of mechanical anharmonicity. The results are compared with the available experimental data. [ABSTRACT FROM AUTHOR]

The Heitler–London (HL) exchange energy is responsible for the anisotropy of the pair potential in methane. The equilibrium dimer structure is that which minimizes steric repulsion between hydrogens belonging to opposite subsystems. Dispersion energy, which represents a dominating attractive contribution, displays an orientation dependence which is the mirror image of that for HL exchange. The three-body correction to the pair potential is a superposition of HL and second-order exchange nonadditivities combined with the Axilrod–Teller dispersion nonadditivity. A great deal of cancellation between these terms results in near additivity of methane interactions in the long and intermediate regions. [ABSTRACT FROM AUTHOR]

The combination of supermolecular Mo\ller–Plesset treatment with the perturbation theory of intermolecular forces is applied in the analysis of the potential energy surface of Ar–NH3. Anisotropy of the self-consistent field (SCF) potential is determined by the first-order exchange repulsion. Second-order dispersion energy, the dominating attractive contribution, is anisotropic in the reciprocal sense to the first-order exchange, i.e., minima in one nearly coincide with maxima in the other. The estimated second-order correlation correction to the exchange effect is nearly as large as a half ΔESCF in the minimum and has a ‘‘smoothing’’ effect on the anisotropy of ε(20)disp. The model which combines ΔESCF with dispersion energy (SCF+D) is not accurate enough to quantitatively describe both radial and angular dependence of interaction energy. Comparison is also made between Ar–NH3 and Ar–PH3, as well as with the Ar dimer. [ABSTRACT FROM AUTHOR]

Nonadditive effects are calculated for (HF)3 and (HCl)3 complexes and analyzed via the combination of perturbation theory of intermolecular forces with Mo\ller–Plesset perturbation theory (MPPT). In both systems the nonadditivity is dominated by the self-consistent field (SCF) deformation effect, i.e., mutual polarization of the monomer wavefunctions. Heitler–London exchange and correlation effects are of secondary importance. Three-body terms exhibit much lesser basis set dependence than the two-body effects and even quite moderate basis sets which are not accurate enough for treatment of two-body forces can yield three-body effects of quantitative quality. This is due in large measure to the additivity of strongly basis set dependent components such as uncorrelated and correlated electrostatics and dispersion. Various approximate models for the three-body potentials and total interaction in the (HF)3 cluster are analyzed from the point of view of their ability to predict the orientation dependence of interaction energy. [ABSTRACT FROM AUTHOR]

This paper presents the first ab initio attempt to reconstruct the observed band profile of the stretching fundamental vFX (X=H,D) in the FX···O(CH3)2 hydrogen-bonded system. The two-dimensional potential energy surface V(rFH,RF···O) is evaluated by means of large basis set SCF calculations. The related force constants up to the fourth order are obtained via the analytical fit to a polynomial expansion. The vibrational problem is solved by means of a variational treatment which includes the effects of mechanical anharmonicity. The side bands of the stretching fundamental vFX are described in terms of the vFX ±nvFX···O combination bands in excellent agreement with experiment. [ABSTRACT FROM AUTHOR]

It is generally agreed on that trabecular bone permeability, a physiologically important quantity, is governed by the material׳s (vascular or intertrabecular) porosity as well as by the viscosity of the pore-filling fluids. Still, there is less agreement on how these two key factors govern bone permeability. In order to shed more light onto this somewhat open issue, we here develop a random homogenization scheme for upscaling Poiseuille flow in the vascular porosity, up to Darcy-type permeability of the overall porous medium “trabecular bone”. The underlying representative volume element of the macroscopic bone material contains two types of phases: a spherical, impermeable extracellular bone matrix phase interacts with interpenetrating cylindrical pore channel phases that are oriented in all different space directions. This type of interaction is modeled by means of a self-consistent homogenization scheme. While the permeability of the bone matrix equals to zero, the permeability of the pore phase is found through expressing the classical Hagen–Poiseuille law for laminar flow in the format of a “micro-Darcy law”. The upscaling scheme contains pore size and porosity as geometrical input variables; however, they can be related to each other, based on well-known relations between porosity and specific bone surface. As two key results, validated through comprehensive experimental data, it appears (i) that the famous Kozeny–Carman constant (which relates bone permeability to the cube of the porosity, the square of the specific surface, as well as to the bone fluid viscosity) needs to be replaced by an again porosity-dependent rational function, and (ii) that the overall bone permeability is strongly affected by the pore fluid viscosity, which, in case of polarized fluids, is strongly increased due to the presence of electrically charged pore walls. [ABSTRACT FROM AUTHOR]

SUMMARY Denosumab, a fully human monoclonal antibody, has been approved for the treatment of postmenopausal osteoporosis. The therapeutic effect of denosumab rests on its ability to inhibit osteoclast differentiation. Here, we present a computational approach on the basis of coupling a pharmacokinetics model of denosumab with a pharmacodynamics model for quantifying the effect of denosumab on bone remodeling. The pharmacodynamics model comprises an integrated systems biology-continuum micromechanics approach, including a bone cell population model, considering the governing biochemical factors of bone remodeling (including the action of denosumab), and a multiscale micromechanics-based bone mechanics model, for implementing the mechanobiology of bone remodeling in our model. Numerical studies of postmenopausal osteoporosis show that denosumab suppresses osteoclast differentiation, thus strongly curtailing bone resorption. Simulation results also suggest that denosumab may trigger a short-term bone volume gain, which is, however, followed by constant or decreasing bone volume. This evolution is accompanied by a dramatic decrease of the bone turnover rate by more than one order of magnitude. The latter proposes dominant occurrence of secondary mineralization (which is not anymore impeded through cellular activity), leading to higher mineral concentration per bone volume. This explains the overall higher bone mineral density observed in denosumab-related clinical studies. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Oil and gas pipelines covered with a mixture of sandy gravel and square-edged stones are subjected to abrasive shear loading steming from temperature-induced displacements of the pipeline in longitudinal direction. This requires wear protection of the outer anti-corrosion film of such pipes. In order to assess appropriate means for protection, adverse settlements on both sides of the soil-covered pipeline are assumed as relevant loading scenario. A nonlinear, elastoplastic, cap model-based Finite Element model delivers the radial stresses exerted onto the pipeline, due to settlement-induced load re-arrangement within the cohesionless soil body. Given a cover height of 1.5m, the aforementioned load re-arrangement leads to an increase of force action onto the pipe by up to 200%. Based on the grain size of the filling material, radial stresses are integrated as to estimate the maximum normal forces exerted by single stone corners onto the pipe’s anti-corrosion film. These forces, when analyzed through Archard’s law, allow for calculation of the service life of the protection layer enveloping the pipe, once the wear resistance of that layer is determined from experiments, as is done for geosynthetics. Since the service life of a geosynthetic protection layer of the anti-corrosion film turns out to be distinctively smaller than the standard service life of a soil-covered steel pipeline, protection through geosynthetic layers is insufficient. Hence, more effective means for protection are suggested. [Copyright &y& Elsevier]

Abstract Laboratory selection experiments are powerful tools for establishing evolutionary potentials. Such experiments provide two types of information, knowledge about genetic architecture and insight into evolutionary dynamics. They can be roughly classified into two types: (1) artificial selection in which the experimenter selects on a focal trait or trait index, and (2) quasi-natural selection in which the experimenter establishes a set of environmental conditions and then allows the population to evolve. Both approaches have been used in the study of phenotypic plasticity. Artificial selection experiments have taken various forms including: selection directly on a reaction norm, selection on a trait in multiple environments, and selection on a trait in a single environment. In the latter experiments, evolution of phenotypic plasticity is investigated as a correlated response. Quasi-natural selection experiments have examined the effects of both spatial and temporal variation. I describe how to carry out such experiments, summarize past efforts, and suggest further avenues of research. [ABSTRACT FROM AUTHOR]

Abstract Laboratory selection experiments are powerful tools for establishing evolutionary potentials. Such experiments provide two types of information, knowledge about genetic architecture and insight into evolutionary dynamics. They can be roughly classified into two types: (1) artificial selection in which the experimenter selects on a focal trait or trait index, and (2) quasi-natural selection in which the experimenter establishes a set of environmental conditions and then allows the population to evolve. Both approaches have been used in the study of phenotypic plasticity. Artificial selection experiments have taken various forms including: selection directly on a reaction norm, selection on a trait in multiple environments, and selection on a trait in a single environment. In the latter experiments, evolution of phenotypic plasticity is investigated as a correlated response. Quasi-natural selection experiments have examined the effects of both spatial and temporal variation. I describe how to carry out such experiments, summarize past efforts, and suggest further avenues of research. [ABSTRACT FROM AUTHOR]

Both island-biogeographic (dynamic) and niche-based (static) metapopulation models make predictions about the distribution and abundance of species assemblages. We tested the utility of these models concerning such predictions for terrestrial vascular plants using data from 74 landscapes across the globe. We examined correlations between species frequency and local abundance and shapes of the species frequencydistribution. No data set met all of the predictions of any single island-biogeographic metapopulation model. In contrast, all data sets met the predictions of the niche-based model. We conclude that in predicting the distribution of species assemblages of plants over scalesgreater than 10-1 km, niche-based models are robust whilecurrent metapopulation models are insufficient. We discuss limitations in the assumptions of the various models and the types of empirical observations that they will each have to deal with in further developments. [ABSTRACT FROM AUTHOR]