Large displacement strain theory and its application to graphene

Under the application of a force, a material will deform and, hence, the crystal lattice will experience strain. This induced strain will alter the electronic properties of the material. In particular, strain in graphene generates an artificial vector potential which, if spatially varying, admits a pseudo-magnetic field. Current theories for spatially varying strain use linear or finite strain theory whose derivation is based on small displacements of infinitesimal length vectors. Here we apply a differential geometry method to derive a strain theory for large displacements of finite length vectors. This method gives a finite displacement term whose contribution is comparable to that of the linear strain term. Further to this, we show that a 'domain wall'-like pseudo-magnetic field profile can be generated when a wide graphene ribbon is subjected to a pair of opposing point forces (point stretch). The resulting field is a function of the new finite displacement term only and displays a maximum strength of over three times that which is predicted by the linear strain theory. These results extend the current theories of strain, which are based on the transformation of infinitesimal length vectors, to finite length vectors, thus providing an accurate description of pseudo-magnetic field structures in strained materials.Comment: Updated to journal version with revised figure 3 and new title. 7 pages, 5 figure

Casimir-Polder Shift and Decay Rate in the Presence of Nonreciprocal Media

We calculate the Casimir-Polder frequency shift and decay rate for an atom in front of a nonreciprocal medium by using macroscopic quantum electrodynamics. The results are a generalization of the respective quantities for matter with broken time-reversal symmetry which does not fulfill the Lorentz reciprocity principle. As examples, we contrast the decay rates, the resonant and nonresonant frequency shifts of a perfectly conducting (reciprocal) mirror to those of a perfectly reflecting nonreciprocal mirror. We find different power laws for the distance dependence of all quantities in the retarded and nonretarded limits. As an example of a more realistic nonreciprocal medium, we investigate a topological insulator subject to a time-symmetry breaking perturbation.Comment: 11 pages, 6 figure

A New Direction for the Payment of Milk: Technological and Seasonality Considerations in Multiple Component Milk Pricing of Milk (Liquid and Manufacturing) for a Diversifying Dairy Industry

End of project reportThe main objectives of this study were to compare a Multiple Component Pricing system with the current milk pricing practice in Ireland and to estimate the marginal values of the three main milk components (fat, protein and lactose) in the context of the Irish milk processing industry. A representative linear programming model of an average Irish milk processor was developed in order to determine the marginal values of the milk components and to compare the value of milk under the Multiple Component Pricing system with the value under the current milk pricing practice. This study also examined the effect of product mix, milk supply and milk composition on the marginal value of the milk components

The Electromagnetic Green's Function for Layered Topological Insulators

The dyadic Green's function of the inhomogeneous vector Helmholtz equation describes the field pattern of a single frequency point source. It appears in the mathematical description of many areas of electromagnetism and optics including both classical and quantum, linear and nonlinear optics, dispersion forces (such as the Casimir and Casimir-Polder forces) and in the dynamics of trapped atoms and molecules. Here, we compute the Green's function for a layered topological insulator. Via the magnetoelectric effect, topological insulators are able to mix the electric, E, and magnetic induction, B, fields and, hence, one finds that the TE and TM polarizations mix on reflection from/transmission through an interface. This leads to novel field patterns close to the surface of a topological insulator.Comment: 16 pages, 9 figure

Démarche d’initiation à la pratique réflexive en formation initiale des professeurs des écoles dans le cadre de leur développement professionnel tout au long de la carrière

Comprend des références bibliographiquesDepuis la rentrée 2016, la formation des Master 2 MEEF proposée au sein de notre établissement s’organise autour du référentiel de compétences national des métiers du professorat et de l’éducation. L’enjeu de la formation n’est pas seulement de développer les compétences nécessaires à l’exercice du métier mais aussi de donner aux professeurs des écoles (PE) en devenir les moyens de se développer professionnellement, tout au long de leur carrière. Afin d’accompagner les étudiants-stagiaires dans leur développement professionnel, deux dispositifs ont été intégrés à la formation : la proposition d’un sujet de recherche lié au développement professionnel du PE, dans le cadre des Travaux Encadrés Personnalisés (TEP) et la mise en place d’une démarche portfolio. Comment donner les moyens aux professionnels en devenir d’agir en praticiens réflexifs ? Comment les amener à saisir l’intérêt d’une telle démarche alors qu’ils commencent tout juste à enseigner ? Comment faire en sorte que cette démarche leur soit utile dans leur formation mais surtout au-delà de leur formation, tout au long de leur carrière ? À travers nos retours d’expérience et les échanges avec les étudiants que nous formons, nous nous intéresserons à la dimension collaborative et à l’individualisation au sein de ces dispositifs qui doivent permettre à chaque étudiant-stagiaire de construire son propre parcours et de le faire évoluer en fonction de ses besoins

Thermal Casimir-Polder shifts in Rydberg atoms near metallic surfaces

The Casimir-Polder (CP) potential and transition rates of a Rydberg atom above a plane metal surface at finite temperature are discussed. As an example, the CP potential and transition rates of a rubidium atom above a copper surface at room temperature is computed. Close to the surface we show that the quadrupole correction to the force is significant and increases with increasing principal quantum number n. For both the CP potential and decay rates one finds that the dominant contribution comes from the longest wavelength transition and the potential is independent of temperature. We provide explicit scaling laws for potential and decay rates as functions of atom-surface distance and principal quantum number of the initial Rydberg state.Comment: Updated to journal version with corrected figures. 4 Pages, 2 figure