The Conical Point in the Ferroelectric Six-Vertex Model

We examine the last unexplored regime of the asymmetric six-vertex model: the low-temperature phase of the so-called ferroelectric model. The original publication of the exact solution, by Sutherland, Yang, and Yang, and various derivations and reviews published afterwards, do not contain many details about this regime. We study the exact solution for this model, by numerical and analytical methods. In particular, we examine the behavior of the model in the vicinity of an unusual coexistence point that we call the ``conical'' point. This point corresponds to additional singularities in the free energy that were not discussed in the original solution. We show analytically that in this point many polarizations coexist, and that unusual scaling properties hold in its vicinity.Comment: 28 pages (LaTeX); 8 postscript figures available on request ([email protected]). Submitted to Journal of Statistical Physics. SFU-DJBJDS-94-0

Phase Separation of Crystal Surfaces: A Lattice Gas Approach

We consider both equilibrium and kinetic aspects of the phase separation (``thermal faceting") of thermodynamically unstable crystal surfaces into a hill--valley structure. The model we study is an Ising lattice gas for a simple cubic crystal with nearest--neighbor attractive interactions and weak next--nearest--neighbor repulsive interactions. It is likely applicable to alkali halides with the sodium chloride structure. Emphasis is placed on the fact that the equilibrium crystal shape can be interpreted as a phase diagram and that the details of its structure tell us into which surface orientations an unstable surface will decompose. We find that, depending on the temperature and growth conditions, a number of interesting behaviors are expected. For a crystal in equilibrium with its vapor, these include a low temperature regime with logarithmically--slow separation into three symmetrically--equivalent facets, and a higher temperature regime where separation proceeds as a power law in time into an entire one--parameter family of surface orientations. For a crystal slightly out of equilibrium with its vapor (slow crystal growth or etching), power--law growth should be the rule at late enough times. However, in the low temperature regime, the rate of separation rapidly decreases as the chemical potential difference between crystal and vapor phases goes to zero.Comment: 16 pages (RevTex 3.0); 12 postscript figures available on request ([email protected]). Submitted to Physical Review E. SFU-JDSDJB-94-0

Op weg naar een veilige schoolomgeving: exploratief onderzoek naar drijfveren en barrières bij haal- en brenggedrag van ouders van schoolkinderen

Ongeveer een derde van alle ouders brengt hun kind(eren) met de auto naar school (CROW, 2016). Bij meer dan de helft van de basisscholen ontstaan gevaarlijke situaties door drukte tijdens het brengen en halen van leerlingen (Esseling, 2015), bijvoorbeeld door parkerende auto’s. Daarnaast doen kinderen minder fietservaring op wanneer ze met de auto naar school gebracht worden (CROW, 2016). Deze situatie is een groeiend punt van zorg (Kluivers, 2018; De Zwaan, 2018). Veilig Verkeer Nederland gaf Publab de opdracht om mogelijkheden voor gedragsinterventies te onderzoeken om het halen en brengen per fiets te stimuleren. Eerdere campagnes waren weinig succesvol en bestaande kennis bood weinig aanknopingspunten voor interventies. In onze studie onderzochten we drijfveren voor het brengen en halen met de auto. Deze drijfveren vertaalden we naar potentieel kansrijke beïnvloedingsstrategieën