Hot Spots and Pseudogaps for Hole- and Electron-Doped High-Temperature Superconductors

Using cluster perturbation theory, it is shown that the spectral weight and pseudogap observed at the Fermi energy in recent Angle Resolved Photoemission Spectroscopy (ARPES) of both electron and hole-doped high-temperature superconductors find their natural explanation within the t-t'-t''-U Hubbard model in two dimensions. The value of the interaction U needed to explain the experiments for electron-doped systems at optimal doping is in the weak to intermediate coupling regime where the t-J model is inappropriate. At strong coupling, short-range correlations suffice to create a pseudogap but at weak coupling long correlation lengths associated with the antiferromagnetic wave vector are necessary.Comment: RevTeX 4, 4 pages, 5 figures (2 in color

Les leçons à tirer de l’expérience de SOS-Églises

Que doivent faire les Acadiens pour s’assurer que leur patrimoine architectural religieux ne soit pas mis en péril par des décisions diocésaines de fermer et de détruire des églises paroissiales qui sont au coeur de leurs communautés? David Tremblay, stratège de la campagne menée par SOS-Églises dans le sud-ouest de l’Ontario pour sauver deux églises patrimoniales menacées de démolition, dégage de son expérience ce qu’il considère comme les éléments principaux d’un plan d’action efficace

Strong-Coupling Perturbation Theory of the Hubbard Model

The strong-coupling perturbation theory of the Hubbard model is presented and carried out to order (t/U)^5 for the one-particle Green function in arbitrary dimension. The spectral weight A(k,omega) is expressed as a Jacobi continued fraction and compared with new Monte-Carlo data of the one-dimensional, half-filled Hubbard model. Different regimes (insulator, conductor and short-range antiferromagnet) are identified in the temperature--hopping integral (T,t) plane. This work completes a first paper on the subject (Phys. Rev. Lett. 80, 5389 (1998)) by providing details on diagrammatic rules and higher-order results. In addition, the non half-filled case, infinite resummations of diagrams and the double occupancy are discussed. Various tests of the method are also presented.Comment: 28 pages, 19 figure

Explaining Sales Pay Strategy Using Agency, Transaction Cost and Resource Dependence Theories

The purpose of this study was to investigate, using data gathered from 325 French-Canadian organizations, the influence of key constructs related to agency, transaction cost and resource dependence theories on the proportion of salary in sales compensation. Level of task programmability, capacity to observe behavior, career opportunities and financial resources offered were associated with an increased use of salary pay. In contrast, difficulty of measuring result outcomes, availability of product/service-related resources and high marginal sales force productivity were associated with decreased use of the salary component. Results supported the argument that integration of multiple theoretical perspectives offered a better explanation of pay policy. However, the results have not supported the ability of market and selling uncertainty to predict the proportion of salary L'objectif de cette étude était d'examiner, auprès d'un échantillon de 325 organisations, l'influence des construits clés relatifs à la théorie de l'agence, la théorie des coûts de transaction et la théorie de la dépendence des ressource sur la proportion du salaire dans l'enveloppe de la rémunération directe du personnel de vente. Le niveau de programmation des tâches, la capacité à observer les comportements, les opportunités de carrière et les ressources financières offertes étaient associés à une augmentation du recours de la composante salariale. En revanche, le degré de difficulté à mesurer les résultats, la disponibilité de ressources reliés aux produits/services et un grand différentiel de performance étaient associés à une diminution de la composante salaire. Les résultats supportent l'argument de l'intégration d'une multitude de perspecttives théoriques pour expliquer le choix des stratégies salariales.Sales, compensation, agency theory, cost analysis theory, resource dependence theory, Représentants aux ventes, rémunération, théorie de l'agence, théorie des coûts de transaction, théorie de la dépendance des ressources

The Role of Organizational Justice in Pay and Employee Benefit Satisfaction, and Its Effects on Work Attitudes

The objective of our study is to provide a complementary approach with regard to organizational justice in the domain of compensation. It presents research undertaken on a sample of six hundred employees in three different Canadian organizations. The results reveal that employees distinguish clearly between pay satisfaction and benefit satisfaction, and that distributive justice perceptions are better predictors of pay satisfaction than procedural justice perceptions. This result is reversed for employee benefit satisfaction: procedural justice perceptions are better predictors than distributive justice perceptions. Lastly, the results show that distributive justice perceptions with regard to pay play a more important role than procedural justice in job satisfaction and satisfaction with the organization. Cet article a pour but d'apporter un éclairage complémentaire en ce qui concerne la justice organisationnelle dans le domaine de la rémunération. On y fait état de recherches réalisées auprès de six cents salariés appartenant à trois organisations canadiennes différentes. Les résultats révèlent que les salariés dissocient bien la satisfaction à l'égard du salaire, de la satisfaction à l'égard des avantages sociaux. Ils montrent également que les perceptions de justice distributives permettent de mieux prédire la satisfaction à l'égard du salaire que les perceptions de justice procédurales. Le résultat est inverse en ce qui concerne la satisfaction à l'égard des avantages sociaux : les perceptions de justice procédurales sont de meilleurs prédicteurs que les perceptions de justice distributives. Ils montrent enfin que la perception de justice distributive concernant les salaires joue un rôle plus important que la justice procédurale dans la satisfaction à l'égard du travail et à l'égard de l'entreprise.Organizational justice, pay and benefit satisfaction, work attitudes, Justice organisationnelle, satisfaction du salaire, satisfaction des avantages sociaux, attitudes au travail

d-Wave superconductivity on the checkerboard Hubbard model at weak and strong coupling

It has been argued that inhomogeneity generally can enhance superconductivity in the cuprate high-Tc materials. To check the validity of this claim, we study d-wave superconductivity on the checkerboard Hubbard model on a square lattice using the Cellular Dynamical Mean Field theory method with an exact diagonalization solver at zero temperature. The d-wave order parameter is computed for various inhomogeneity levels over the entire doping range of interest in both strong and weak coupling regimes. At a given doping, the size of the d-wave order parameter manifests itself directly in the height of the coherence peaks and hence is an appropriate measure of the strength of superconductivity. The weak coupling results reveal a suppression of the order parameter in the presence of inhomogeneity for small to intermediate hole dopings, while it is enhanced for large dopings. In contrast, for strong coupling there is a monotonic decrease in the maximum amplitude of the superconducting order parameter with inhomogeneity over the entire doping range of interest. Furthermore, at moderately high inhomogeneity, the system undergoes a first-order transition from the superconducting to the normal state in the underdoped regime. In the overdoped regime, the change in the value of the superconducting order parameter correlates with the height of the lowest energy peak in the spectral weight of antiferromagnetic spin fluctuations, confirming the connection between antiferromagnetic fluctuations and d-wave superconductivity found in earlier studies on the homogeneous case. Our results are benchmarked by comparisons with numerically exact results on the checkerboard Hubbard ladder.Comment: Expanded version includes results on checkerboard Hubbard ladder: 10 pages, 12 figure

Neon diffusion kinetics and implications for cosmogenic neon paleothermometry in feldspars

Observations of cosmogenic neon concentrations in feldspars can potentially be used to constrain the surface exposure duration or surface temperature history of geologic samples. The applicability of cosmogenic neon to either application depends on the temperature-dependent diffusivity of neon isotopes. In this work, we investigate the kinetics of neon diffusion in feldspars of different compositions and geologic origins through stepwise degassing experiments on single, proton-irradiated crystals. To understand the potential causes of complex diffusion behavior that is sometimes manifest as nonlinearity in Arrhenius plots, we compare our results to argon stepwise degassing experiments previously conducted on the same feldspars. Many of the feldspars we studied exhibit linear Arrhenius behavior for neon whereas argon degassing from the same feldspars did not. This suggests that nonlinear behavior in argon experiments is an artifact of structural changes during laboratory heating. However, other feldspars that we examined exhibit nonlinear Arrhenius behavior for neon diffusion at temperatures far below any known structural changes, which suggests that some preexisting material property is responsible for the complex behavior. In general, neon diffusion kinetics vary widely across the different feldspars studied, with estimated activation energies (Ea) ranging from 83.3 to 110.7 kJ/mol and apparent pre-exponential factors (D0) spanning three orders of magnitude from 2.4 × 10−3 to 8.9 × 10−1 cm2 s−1. As a consequence of this variability, the ability to reconstruct temperatures or exposure durations from cosmogenic neon abundances will depend on both the specific feldspar and the surface temperature conditions at the geologic site of interest

Evidence from Intrinsic Shapes for Two Families of Elliptical Galaxies

Bright elliptical galaxies have a markedly different distribution of Hubble types than faint ellipticals; the division occurs near M_B=-20 and bright ellipticals are rounder on average. The Hubble types of galaxies in both groups are narrowly clustered, around E1.5 in the case of the bright galaxies and around E3 for the fainter ones. The Hubble-type distribution of the faint ellipticals is consistent with oblate symmetry, but the oblate hypothesis fails for the bright ellipticals. However a distribution of triaxial intrinsic shapes can successfully reproduce the apparent shape data for either group. The distribution of intrinsic, short-to-long axis ratios is peaked around 0.75 for bright galaxies and 0.65 for faint galaxies. Our results provide further evidence that elliptical galaxies should be divided into two, morphologically distinct families.Comment: 9 TEX pages, 4 PostScript figures, uses AASTEX, epsf.sty. Submitted to The Astronomical Journal, January 1996; revised February 199