A Scalar Wigner Theory for Polarized Light in Nonlinear Kerr Media

A scalar Wigner distribution function for describing polarized light is proposed in analogy with the treatment of spin variables in quantum kinetic theory. The formalism is applied to the propagation of circularly polarized light in nonlinear Kerr media and an extended phase space evolution equation is derived along with invariant quantities. We further consider modulation instability as well as the extension to partially coherent fields.Comment: 6 page

Critical Scaling Properties at the Superfluid Transition of 4^4He in Aerogel

We study the superfluid transition of $^4$He in aerogel by Monte Carlo simulations and finite size scaling analysis. Aerogel is a highly porous silica glass, which we model by a diffusion limited cluster aggregation model. The superfluid is modeled by a three dimensional XY model, with excluded bonds to sites on the aerogel cluster. We obtain the correlation length exponent $\nu=0.73 \pm 0.02$, in reasonable agreement with experiments and with previous simulations. For the heat capacity exponent $\alpha$, both experiments and previous simulations suggest deviations from the Josephson hyperscaling relation $\alpha=2-d\nu$. In contrast, our Monte Carlo results support hyperscaling with $\alpha= -0.2\pm 0.05$. We suggest a reinterpretation of previous experiments, which avoids scaling violations and is consistent with our simulation results.Comment: 4 pages, 3 figure

Observations and models of star formation in the tidal features of interacting galaxies

Multi-color surface photometry (BVri) is presented for the tidal features in a sample of interacting galaxies. Large color variations are found between the morphological components and within the individual components. The blue colors in the primary and the tidal features are most dramatic in B-V, and not in V-i, indicating that star formation instead of metallicity or age dominates the colors. Color variations between components is larger in systems shortly after interaction begins and diminishes to a very low level in systems which are merged. Photometric models for interacting systems are presented which suggest that a weak burst of star formation in the tidal features could cause the observed color distributions. Dynamical models indicate that compression occurs during the development of tidal features causing an increase in the local density by a factor of between 1.5 and 5. Assuming this density increase can be related to the star formation rate by a Schmidt law, the density increases observed in the dynamical models may be responsible for the variations in color seen in some of the interacting systems. Limitations of the dynamical models are also discussed

The Effect of Columnar Disorder on the Superconducting Transition of a Type-II Superconductor in Zero Applied Magnetic Field

We investigate the effect of random columnar disorder on the superconducting phase transition of a type-II superconductor in zero applied magnetic field using numerical simulations of three dimensional XY and vortex loop models. We consider both an unscreened model, in which the bare magnetic penetration length is approximated as infinite, and a strongly screened model, in which the magnetic penetration length is of order the vortex core radius. We consider both equilibrium and dynamic critical exponents. We show that, as in the disorder free case, the equilibrium transitions of the unscreened and strongly screened models lie in the same universality class, however scaling is now anisotropic. We find for the correlation length exponent $\nu=1.2\pm 0.1$, and for the anisotropy exponent $\zeta=1.3\pm 0.1$. We find different dynamic critical exponents for the unscreened and strongly screened models.Comment: 30 pages 12 ps figure

The Teaching Principal: An Untenable Position or a Promising Model?

This paper reports on an interpretive study that examined the role of the teaching principal, particularly as it relates to principals’ moral and legal requirement to work as instructional leaders for student learning. A teaching principal is defined as a principal who has a “double load” or dual roles in teaching and administration (Clarke & Stevens, 2009). In this study, we explored the constitution and effects of this role on individuals and leadership practices of 12 rural teaching principals in Alberta and Manitoba. Findings reflect the need to develop policies that sustain the smaller schools which depend upon administrators capable of thriving in this dual role. Additionally, the way in which teaching principals practice as instructional leaders promises to enrich the literature on instructional leadership. Specifically, the practices that emerge through the teaching principalship are a unique adaptation of existing conceptualizations that offer considerable advantages over those that presuppose a full-time administrative appointment. Cet article rend compte d’une étude interprétative portant sur le rôle du directeur enseignant, notamment par rapport à l’exigence morale et juridique qu’ont les directeurs de travailler comme leaders pédagogiques. Un directeur enseignant en est un qui a une « double charge », qui joue deux rôles, un en enseignement et un en administration (Clarke & Stevens, 2009). Dans cette étude, nous avons exploré la création et les effets de ce rôle sur les individus et sur les pratiques de leadership de douze directeurs enseignants en milieu rural en Alberta et au Manitoba. Les résultats reflètent la nécessité de développer des politiques qui appuient les plus petites écoles qui dépendent d’administrateurs en mesure de prospérer dans le contexte de ce double rôle. De plus, les pratiques qu’emploient les directeurs enseignants dans leur capacité de leaders pédagogiques promettent d’enrichir la littérature sur le leadership pédagogique. Plus spécifiquement, les pratiques qui ressortent des pratiques des directeurs enseignants constituent une adaptation unique des conceptualisations existantes, une qui offre un nombre considérable d’avantages par rapport à celles qui présupposent un poste administratif à temps plein

Broadband, unpolarized repumping and clearout light sources for Sr+^+ single-ion clocks

Future transportable optical clocks require compact and reliable light sources. Here, broadband, unpolarized repumper and state clearout sources for Sr+ single-ion optical clocks are reported. These turn-key devices require no frequency stabilization nor external modulators. They are fiber based, inexpensive, and compact. Key characteristics for clock operation are presented, including optical spectra, induced light shifts and required extinction ratios. Tests with an operating single-ion standard show a clearout efficiency of 100%. Compared to a laser-based repumper, the achievable fluorescence rates for ion detection are a few tens of per cent lower. The resulting ion kinetic temperature is 1--1.5 mK, near the Doppler limit of the ion system. Similar repumper light sources could be made for Ca+ (866 nm) and Ba+ (650 nm) using semiconductor gain media.Comment: 4 pages, 6 figure