Thermodynamic parameters of bonds in glassy materials from viscosity-temperature relationships

Doremus's model of viscosity assumes that viscous flow in amorphous materials is mediated by broken bonds (configurons). The resulting equation contains four coefficients, which are directly related to the entropies and enthalpies of formation and motion of the configurons. Thus by fitting this viscosity equation to experimental viscosity data these enthalpy and entropy terms can be obtained. The non-linear nature of the equation obtained means that the fitting process is non-trivial. A genetic algorithm based approach has been developed to fit the equation to experimental viscosity data for a number of glassy materials, including SiO2, GeO2, B2O3, anorthite, diopside, xNa2O–(1-x)SiO2, xPbO–(1-x)SiO2, soda-lime-silica glasses, salol, and α-phenyl-o-cresol. Excellent fits of the equation to the viscosity data were obtained over the entire temperature range. The fitting parameters were used to quantitatively determine the enthalpies and entropies of formation and motion of configurons in the analysed systems and the activation energies for flow at high and low temperatures as well as fragility ratios using the Doremus criterion for fragility. A direct anti-correlation between fragility ratio and configuron percolation threshold, which determines the glass transition temperature in the analysed materials, was found

Composition, nanostructure, and optical properties of silver and silver-copper lusters

Lusters are composite thin layers of coinage metal nanoparticles in glass displaying peculiar optical properties and obtained by a process involving ionic exchange, diffusion, and crystallization. In particular, the origin of the high reflectance (golden-shine) shown by those layers has been subject of some discussion. It has been attributed to either the presence of larger particles, thinner multiple layers or higher volume fraction of nanoparticles. The object of this paper is to clarify this for which a set of laboratory designed lusters are analysed by Rutherford backscattering spectroscopy, transmission electron microscopy, x-ray diffraction, and ultraviolet-visible spectroscopy. Model calculations and numerical simulations using the finite difference time domain method were also performed to evaluate the optical properties. Finally, the correlation between synthesis conditions, nanostructure, and optical properties is obtained for these materials

Computational Modeling of Silicate Glasses: A Quantitative Structure-Property Relationship Perspective

This article reviews the present state of Quantitative Structure-Property Relationships (QSPR) in glass design and gives an outlook into future developments. First an overview is given of the statistical methodology, with particular emphasis to the integration of QSPR with molecular dynamics simulations to derive informative structural descriptors. Then, the potentiality of this approach as a tool for interpretative and predictive purposes is highlighted by a number of recent inspiring applications

Interplay of lean thinking and social dynamics in construction

Production, commercial, technical, organizational and social aspects must be managed simultaneously for a construction project to be successfully delivered. However, most management approaches in construction are technically-oriented methodologies that largely neglect central social aspects related to people's behaviour. Lean construction research has likewise focused more on technical and commercial aspects than on social aspects. Recent research in the domain has aroused interest in various social aspects, such as the language-Action-perspective, people development, culture and transformation, and integral theory. Yet little research has been pursued to understand the interactions between lean construction thinking and the social dynamics within construction project organizations. To begin to bridge this gap, the latent synergy and feedback loops between lean construction practices and social dynamics variables such as trust, goal setting and power distance in construction are discussed in this paper. The interplay between lean construction tools and the social dynamics variables is illustrated through an example based on the Last Planner System (LPS). We argue that lean tools work better when the environment is less autocratic, the team is more integrated, and the levels of trust between project team members are higher. In this organizational environment power-distance is decreased. Lean and goal setting also seem to interact positively and motivate the team