Physical Model for Plaque Action in the Tooth-Plaque-Saliva System

A physical model describing the interrelationships of demineralization, remineralization, plaque thickness, glucose levels, and plaque enzymatic activity was presented. Selection of constants and variations of the parameters were kept in the range of possible in vivo situations. The results of calculations were discussed and correlated with the results of in vivo studies.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66483/2/10.1177_00220345700490013001.pd

Correlation Functions for Diffusion-Limited Annihilation, A + A -> 0

The full hierarchy of multiple-point correlation functions for diffusion-limited annihilation, A + A -> 0, is obtained analytically and explicitly, following the method of intervals. In the long time asymptotic limit, the correlation functions of annihilation are identical to those of coalescence, A + A -> A, despite differences between the two models in other statistical measures, such as the interparticle distribution function

Ab initio atomistic thermodynamics and statistical mechanics of surface properties and functions

Previous and present "academic" research aiming at atomic scale understanding is mainly concerned with the study of individual molecular processes possibly underlying materials science applications. Appealing properties of an individual process are then frequently discussed in terms of their direct importance for the envisioned material function, or reciprocally, the function of materials is somehow believed to be understandable by essentially one prominent elementary process only. What is often overlooked in this approach is that in macroscopic systems of technological relevance typically a large number of distinct atomic scale processes take place. Which of them are decisive for observable system properties and functions is then not only determined by the detailed individual properties of each process alone, but in many, if not most cases also the interplay of all processes, i.e. how they act together, plays a crucial role. For a "predictive materials science modeling with microscopic understanding", a description that treats the statistical interplay of a large number of microscopically well-described elementary processes must therefore be applied. Modern electronic structure theory methods such as DFT have become a standard tool for the accurate description of individual molecular processes. Here, we discuss the present status of emerging methodologies which attempt to achieve a (hopefully seamless) match of DFT with concepts from statistical mechanics or thermodynamics, in order to also address the interplay of the various molecular processes. The new quality of, and the novel insights that can be gained by, such techniques is illustrated by how they allow the description of crystal surfaces in contact with realistic gas-phase environments.Comment: 24 pages including 17 figures, related publications can be found at http://www.fhi-berlin.mpg.de/th/paper.htm

The origin of reactivity bands in atom-molecule collisions

Classical trajectories are calculated on model designed to reproduce the reactive-unreactive bands found with the SSMK and Yates-Lester surfaces for the H + H2 system and other A + BC systems. The model surfaces are based on a rectilinear reaction path, with a constant period of vibration, and have an exit region corresponding to reaction. A simple surface obtained by taking a cut at constant RBC though a collinear potential-energy function is not as satisfactory as one to which a platform has been added to allow for the zero-point energy normal to the minimum reaction path. General principles are derived for obtaining reaction probabilities and reactive-unreactive boundaries for such surfaces. The model surfaces predict the bands in a general way, and throw light on the reason they occur, but do not lead to quantitative predictions

Energy bands in reactive collisions. I. H+H2 on the collinear SSMK surface

The collision of H+H2 on the collinear Shavitt, Stevens, Minn, and Karplus (SSMK) surface is studied for incident energies of 0-2 eV. By assuming a fixed zero-point energy for H2, and systematically varying the incident energy of the atom and the vibrational phase angle of the molecule, the trajectories divide into a continuous series of reactive (R) and unreactive (U) bands. At the R-U boundary, trajectory times and product vibrational energies reach a maximum. From the bands, the reaction probability may be obtained with a high degree of precision. Band continuity is shown clearly by means of linear and polar plots. The reaction probabilities obtained from the band plots are discussed and compared to other quasiclassical and quantum-mechanical studies. Copyrigh