Polarization Light Curve Modeling of Corotating Interaction Regions in the Wind of the Wolf-Rayet Star WR 6

The intriguing WN4b star WR6 has been known to display epoch-dependent spectroscopic, photometric and polarimetric variability for several decades. In this paper, we set out to verify if a simplified analytical model in which Corotating Interaction Regions (CIRs) threading an otherwise spherical wind is able to reproduce the many broadband continuum light curves from the literature with a reasonable set of parameters. We modified the optically thin model we developed in Ignace, St-Louis & Proulx-Giraldeau (2015) to approximately account for multiple scattering and used it to fit 13 separate datasets of this star. By including two CIRs in the wind, we obtained reasonable fits for all datasets with coherent values for the inclination of the rotation axis ($i_0=166^{\circ}$) and for its orientation in the plane of the sky, although in the latter case we obtained two equally acceptable values ($\psi=63^{\circ}$ and $\psi=152^{\circ}$) from the polarimetry. Additional line profile variation simulations using the Sobolev approximation for the line transfer allowed us to eliminate the $\psi=152^{\circ}$ solution. With the adopted configuration ($i_0=166^{\circ}$ and $\psi=63^{\circ}$), we were able to reproduce all datasets relatively well with two CIRs located near the stellar equator and always separated by $\sim 90^{\circ}$ in longitude. The epoch-dependency comes from the fact that these CIRs migrate along the surface of the star. Density contrasts smaller than a factor of two and large opening angles for the CIR ($\beta \geq 35^{\circ}$) were found to best reproduce the type of spectroscopic variability reported in the literature.Comment: 15 pages, 5 figures,5 table

Benchmark of a modified Iterated Perturbation Theory approach on the 3d FCC lattice at strong coupling

The Dynamical Mean-Field theory (DMFT) approach to the Hubbard model requires a method to solve the problem of a quantum impurity in a bath of non-interacting electrons. Iterated Perturbation Theory (IPT) has proven its effectiveness as a solver in many cases of interest. Based on general principles and on comparisons with an essentially exact Continuous-Time Quantum Monte Carlo (CTQMC) solver, here we show that the standard implementation of IPT fails away from half-filling when the interaction strength is much larger than the bandwidth. We propose a slight modification to the IPT algorithm that replaces one of the equations by the requirement that double occupancy calculated with IPT gives the correct value. We call this method IPT-$D$. We recover the Fermi liquid ground state away from half-filling. The Fermi liquid parameters, density of states, chemical potential, energy and specific heat on the FCC lattice are calculated with both IPT-$D$ and CTQMC as benchmark examples. We also calculated the resistivity and the optical conductivity within IPT-$D$. Particle-hole asymmetry persists even at coupling twice the bandwidth. Several algorithms that speed up the calculations are described in appendices.Comment: 17 pages, 15 figures, minor changes to improve clarit

The Role of Organizational Commitment and Citizenship Behaviors in Understanding Relations between Human Resources Practices and Turnover Intentions of IT Personnel

The primary objective of this study is to present and test an integrated model of turnover intentions which addresses the unique nature of the information technology (IT) profession. It identifies a multidimensional set of human resources (HR) practices likely to increase retention among IT employees. It also considers organizational citizenship behaviors and two distinct types of organizational commitment as key antecedents of turnover intentions. A second goal is to explore the moderating effects of organizational commitment and citizenship behaviors on HR practices-turnover intention relationships. A questionnaire was developed and sent to the Québec members of the Canadian Information Processing Society. Data from 394 respondents were used to validate the measures and test the research model. Findings reveal that IT specialists are particularly sensitive to four types of HR policies and practices: distributive justice, competence development, empowerment, and recognition. Results also provide additional support for the generalizability of the two-component model of organizational commitment in the IT context. This study is the first to show that the effects of various HR practices on turnover intentions among IT specialists depend upon the nature of their commitment to the organization. Similarly, we found that citizenship behaviors not only mediate but also moderate HR practicesturnover intention relationships. Implications of these results for practice and research are discussed. Dans cette étude, nous présentons et testons un modèle de recherche portant sur la rétention des spécialistes en TI. Ce modèle examine les relations entre diverses pratiques de GRH, les comportements discrétionnaires, l'engagement organisationnel et les intentions de quitter des spécialistes en TI. Un questionnaire fût développé et envoyé aux membres de la Fédération de l'Informatique du Québec (FIQ). Les données de 394 questionnaires ont servi aux fins d'analyses statistiques. Les résultats de cette étude révèlent que les spécialistes en TI au Québec sont particulièrement sensibles à quatre types de pratiques de GRH, soit: la justice distributive, la reconnaissance non-monétaire, le développement des compétences professionnelles et la responsabilisation. Notre étude est également la toute première à démontrer clairement que l'impact des pratiques de GRH sur l'intention de quitter des spécialistes en TI dépend à la fois du niveau d'engagement et de mobilisation des employés. Nos résultats confirment enfin l'importance relative de deux formes distinctes d'engagement organisationnel (affectif et continu) dans un tel contexte. Sur la base des résultats obtenus, nous faisons une série de recommandations aux hauts dirigeants.IS staffing issues, IS turnover, HRM practices, Gestion du personnel en TI, roulement du personnel en TI, pratiques de GRH

Fano Resonances in Mid-Infrared Spectra of Single-Walled Carbon Nanotubes

This work revisits the physics giving rise to the carbon nanotubes phonon bands in the mid- infrared. Our measurements of doped and undoped samples of single-walled carbon nanotubes in Fourier transform infrared spectroscopy show that the phonon bands exhibit an asymmetric lineshape and that their effective cross-section is enhanced upon doping. We relate these observations to electron-phonon coupling or, more specifically, to a Fano resonance phenomenon. We note that only the dopant-induced intraband continuum couples to the phonon modes and that defects induced in the sidewall increase the resonance probabilities.Comment: 5 pages, 4 figures and 1 Supplementary Information File (in pdf