Theory of ice premelting in porous media

Premelting describes the confluence of phenomena that are responsible for the stable existence of the liquid phase of matter in the solid region of its bulk phase diagram. Here we develop a theoretical description of the premelting of water ice contained in a porous matrix, made of a material with a melting temperature substantially larger than ice itself, to predict the amount of liquid water in the matrix at temperatures below its bulk freezing point. Our theory combines the interfacial premelting of ice in contact with the matrix, grain boundary melting in the ice, and impurity and curvature induced premelting, the latter occurring in regions which force the ice-liquid interface into a high curvature configuration. These regions are typically found at points where the matrix surface is concave, along contact lines of a grain boundary with the matrix, and in liquid veins. Both interfacial premelting and curvature induced premelting depend on the concentration of impurities in the liquid, which, due to the small segregation coefficient of impurities in ice are treated as homogeneously distributed in the premelted liquid. Our principal result is an equation for the fraction of liquid in the porous medium as a function of the undercooling, which embodies the combined effects of interfacial premelting, curvature induced premelting, and impurities. The result is analyzed in detail and applied to a range of experimentally relevant settings.Comment: 14 pages, 10 figures, accepted for publication in Physical Review

A fundamental measure theory for the sticky hard sphere fluid

We construct a density functional theory (DFT) for the sticky hard sphere (SHS) fluid which, like Rosenfeld's fundamental measure theory (FMT) for the hard sphere fluid [Phys. Rev. Lett. {\bf 63}, 980 (1989)], is based on a set of weighted densities and an exact result from scaled particle theory (SPT). It is demonstrated that the excess free energy density of the inhomogeneous SHS fluid $\Phi_{\text{SHS}}$ is uniquely defined when (a) it is solely a function of the weighted densities from Kierlik and Rosinberg's version of FMT [Phys. Rev. A {\bf 42}, 3382 (1990)], (b) it satisfies the SPT differential equation, and (c) it yields any given direct correlation function (DCF) from the class of generalized Percus-Yevick closures introduced by Gazzillo and Giacometti [J. Chem. Phys. {\bf 120}, 4742 (2004)]. The resulting DFT is shown to be in very good agreement with simulation data. In particular, this FMT yields the correct contact value of the density profiles with no adjustable parameters. Rather than requiring higher order DCFs, such as perturbative DFTs, our SHS FMT produces them. Interestingly, although equivalent to Kierlik and Rosinberg's FMT in the case of hard spheres, the set of weighted densities used for Rosenfeld's original FMT is insufficient for constructing a DFT which yields the SHS DCF.Comment: 11 pages, 3 figure

Grain boundary melting in ice

We describe an optical scattering study of grain boundary premelting in water ice. Ubiquitous long ranged attractive polarization forces act to suppress grain boundary melting whereas repulsive forces originating in screened Coulomb interactions and classical colligative effects enhance it. The liquid enhancing effects can be manipulated by adding dopant ions to the system. For all measured grain boundaries this leads to increasing premelted film thickness with increasing electrolyte concentration. Although we understand that the interfacial surface charge densities $q_s$ and solute concentrations can potentially dominate the film thickness, we can not directly measure them within a given grain boundary. Therefore, as a framework for interpreting the data we consider two appropriate $q_s$ dependent limits; one is dominated by the colligative effect and one is dominated by electrostatic interactions.Comment: 6 pages, 5 figure

Role of beam propagation in Goos-H\"{a}nchen and Imbert-Fedorov shifts

We derive the polarization-dependent displacements parallel and perpendicular to the plane of incidence, for a Gaussian light beam reflected from a planar interface, taking into account the propagation of the beam. Using a classical-optics formalism we show that beam propagation may greatly affect both Goos-H\"{a}nchen and Imbert-Fedorov shifts when the incident beam is focussed.Comment: 3 pages, 1 figure, submitted to Opt. Let

Scarred Resonances and Steady Probability Distribution in a Chaotic Microcavity

We investigate scarred resonances of a stadium-shaped chaotic microcavity. It is shown that two components with different chirality of the scarring pattern are slightly rotated in opposite ways from the underlying unstable periodic orbit, when the incident angles of the scarring pattern are close to the critical angle for total internal reflection. In addition, the correspondence of emission pattern with the scarring pattern disappears when the incident angles are much larger than the critical angle. The steady probability distribution gives a consistent explanation about these interesting phenomena and makes it possible to expect the emission pattern in the latter case.Comment: 4 pages, 5 figure

A hard-sphere model on generalized Bethe lattices: Statics

We analyze the phase diagram of a model of hard spheres of chemical radius one, which is defined over a generalized Bethe lattice containing short loops. We find a liquid, two different crystalline, a glassy and an unusual crystalline glassy phase. Special attention is also paid to the close-packing limit in the glassy phase. All analytical results are cross-checked by numerical Monte-Carlo simulations.Comment: 24 pages, revised versio

A sociocultural analysis of the development of pre-service and beginning teachers’ pedagogical identities as users of technology

This paper reports on a study that investigated the pedagogical practices and beliefs of pre-service and beginning teachers in integrating technology into the teaching of secondary school mathematics. A case study documents how one teachers modes of working with technology changed over time and across different school contexts, and identifies relationships between a range of personal and contextual factors that influenced the development of his identity as a teacher. This analysis views teachers learning as increasing participation in sociocultural practices, and uses Valsiners concepts of the Zone of Proximal Development, Zone of Free Movement, and Zone of Promoted Action to offer a dynamic way of theorising teacher learning as identity formation

An Evidence-based Framework for Reporting Student Nurse Medication Incidents: Errors, Near Misses and Discovered Errors

Purpose: To share an evidence-based framework for reporting and analysing three types of medication incidents in an undergraduate nursing program. Incident types include errors, near misses and discovered errors. Background: Medication errors are underreported. Published studies on errors by nursing students indicate that although errors occur during clinical placements, there is a lack of consensus on how the factors that contributed to the errors are reported and analyzed. This limits our understanding of the factors that impact safe medication administration and reduces our ability to apply this knowledge to education and practice. Method: Quality improvement project. Results: Our reporting framework quantifies system factors that are supported by the literature as contributing to errors but not usually captured in incident reporting. Contributing factors for errors and near misses varied. This finding has not been documented in the literature. Conclusion: Nursing schools should prepare nursing students with a strong commitment to report all incidents and provide them with the competencies and a reporting system that allows them to report efficiently and effectively. As these graduates enter the workforce, they can influence the reporting practices of seasoned nurses. The ten factor framework provides nursing schools with the ability to quantify the individual and system factors that influence the safety of the student nurse medication administration process and the opportunity to implement strategies to reduce and/or prevent these incidents from occurring. Objectif : Présenter un cadre fondé sur des résultats probants pour signaler et analyser trois types d’incidents liés aux médicaments dans un programme de premier cycle en sciences infirmières, soit les erreurs, les quasi-incidents et les erreurs découvertes. Contexte : Les erreurs de médication ne sont pas toutes signalées. Les études publiées portant sur les erreurs causées par des étudiantes infirmières indiquent que, même si les erreurs se produisent durant les stages cliniques, la manière de signaler et d’analyser les facteurs contributifs ne fait pas consensus. Cela limite notre compréhension des facteurs influant sur l’administration sécuritaire des médicaments et réduit notre capacité à mettre en application ces connaissances en formation et en pratique. Méthode : Projet d’amélioration de la qualité. Résultats : Notre cadre de signalements quantifie les facteurs systémiques qui, selon la littérature sur le sujet, contribuent à des erreurs, mais ne figurent pas normalement dans les déclarations d’incident. Les facteurs ayant contribué à des erreurs et quasi-incidents étaient variables. Ce résultat n’a pas été rapporté dans la littérature. Conclusion : Les écoles de sciences infirmières devraient enseigner aux étudiantes infirmières l’importance de signaler l’ensemble des incidents tout en leur fournissant les habiletés et un système de déclaration qui leur permet de les déclarer de façon efficace et efficiente. Lorsque les diplômées intègreront le marché du travail, elles pourront influencer les pratiques des infirmières chevronnées en matière de signalement. Le cadre composé de dix facteurs permet aux écoles de sciences infirmières de quantifier les facteurs individuels et systémiques ayant un impact sur la sécurité du processus d’administration des médicaments par des étudiantes infirmières; il leur permet aussi de mettre en œuvre des stratégies de réduction ou de prévention de tels incidents

Phase behaviour of binary mixtures of diamagnetic colloidal platelets in an external magnetic field

Using fundamental measure density functional theory we investigate paranematic-nematic and nematic-nematic phase coexistence in binary mixtures of circular platelets with vanishing thicknesses. An external magnetic field induces uniaxial alignment and acts on the platelets with a strength that is taken to scale with the platelet area. At particle diameter ratio lambda=1.5 the system displays paranematic-nematic coexistence. For lambda=2, demixing into two nematic states with different compositions also occurs, between an upper critical point and a paranematic-nematic-nematic triple point. Increasing the field strength leads to shrinking of the coexistence regions. At high enough field strength a closed loop of immiscibility is induced and phase coexistence vanishes at a double critical point above which the system is homogeneously nematic. For lambda=2.5, besides paranematic-nematic coexistence, there is nematic-nematic coexistence which persists and hence does not end in a critical point. The partial orientational order parameters along the binodals vary strongly with composition and connect smoothly for each species when closed loops of immiscibility are present in the corresponding phase diagram.Comment: 9 pages, to appear in J.Phys:Condensed Matte