Tracking Thermo-Oxidation Reaction Products and Pathways of Modified Lignin Structures from Reactive Molecular Dynamics Simulations.

Thermo-oxidation of biomass is an important process that occurs through a variety of reaction pathways depending on the chemical nature of the molecules and reaction conditions. These processes can be modeled using reactive molecular dynamics to study chemical reactions and the evolution of converted molecules over time. The advantage of this approach is that many molecules can be modeled, but it is challenging to use the large amount of data obtained from such a simulation to determine reaction products and pathways. In this study, we developed a tracking approach to identify the reaction pathways of the dominant reaction products from reactive molecular dynamics simulations. We demonstrated the approach for thermo-oxidation reactions of modified model lignin compounds. For two modified lignin structures, we tracked the evolving chemical species to find the most common reaction products. Subsequently, we monitored specific bonds to determine the individual steps in the reaction process. This combined approach of reactive molecular dynamics and tracking enabled us to identify the most likely thermo-oxidation pathways. The methodology can be used to investigate the thermo-oxidative pathways of a wider range of chemical compounds.

Applicability of Macroscopic Wear and Friction Laws on the Atomic Length Scale.

Using molecular dynamics, we simulate the abrasion process of an atomically rough Fe surface with multiple hard abrasive particles. By quantifying the nanoscopic wear depth in a time-resolved fashion, we show that Barwell's macroscopic wear law can be applied at the atomic scale. We find that in this multiasperity contact system, the Bowden-Tabor term, which describes the friction force as a function of the real nanoscopic contact area, can predict the kinetic friction even when wear is involved. From this the Derjaguin-Amontons-Coulomb friction law can be recovered, since we observe a linear dependence of the contact area on the applied load in accordance with Greenwood-Williamson contact mechanics.

Seismic vulnerability of equipment in critical facilities : Life-safety and operational consequences

This study is part of a multi-year program aimed toward reducing earthquake risk for critical facility equipment and components. The program goal is to determine which equipment components are critical to life safety and normal operations, and how equipment systems have perfomed in past earthquakes. This report represents the dirst program phase, in which equipment data were collected and reviewed in the context of four sample facility types and six equipment systems. Subsequent program phases will: (i) develop a simplified method to assess and improve the reliability of equipment systems, (ii) apply the methodology to example building and component inventories, and (iii) disseminate component fragility and system reliability models in a format that can be used by codewriting bodies, emergency-response facility owners, and operators of economically valuable facilities.(AU)