Quantum Hall Transition in the Classical Limit

We study the quantum Hall transition using the density-density correlation function. We show that in the limit h->0 the electron density moves along the percolating trajectories, undergoing normal diffusion. The localization exponent coincides with its percolation value \nu=4/3. The framework provides a natural way to study the renormalization group flow from percolation to quantum Hall transition. We also confirm numerically that the critical conductivity of a classical limit of quantum Hall transition is \sigma_{xx} = \sqrt{3}/4.Comment: 8 pages, 4 figures; substantial changes include the critical conductivity calculatio

Give it up for climate change : a defence of the beneficiary pays principle

This article focuses on the normative problem of establishing how the burdens associated with implementing policies designed to prevent, or manage, climate change should be shared amongst states involved in ongoing international climate change negotiations. This problem has three key features: identifying the nature and extent of the burdens that need to be borne; identifying the type of agent that should be allocated these burdens; and distributing amongst the particular ‘tokens’ of the relevant ‘agent type’ climatic burdens according to principles that none could reasonably reject. The article defends a key role in climatic burden-sharing policy for the principle that states benefiting most from activities that cause climate change should bear the greatest burden in terms of the costs of preventing dangerous climate change. I outline two versions of this ‘beneficiary pays’ principle; examine the strengths and weakness of each version; and explore how the most plausible version (which I call the ‘unjust enrichment’ account) could be operationalized in the context of global climate governance

Monte-Carlo study of scaling exponents of rough surfaces and correlated percolation

We calculate the scaling exponents of the two-dimensional correlated percolation cluster's hull and unscreened perimeter. Correlations are introduced through an underlying correlated random potential, which is used to define the state of bonds of a two-dimensional bond percolation model. Monte-Carlo simulations are run and the values of the scaling exponents are determined as functions of the Hurst exponent H in the range -0.75 <= H <= 1. The results confirm the conjectures of earlier studies

Short and Long Range Screening of Optical Singularities

Screening of topological charges (singularities) is discussed for paraxial optical fields with short and with long range correlations. For short range screening the charge variance in a circular region with radius $R$ grows linearly with $R$, instead of with $R^{2}$ as expected in the absence of screening; for long range screening it grows faster than $R$: for a field whose autocorrelation function is the zero order Bessel function J_{0}, the charge variance grows as R ln R$. A J_{0} correlation function is not attainable in practice, but we show how to generate an optical field whose correlation function closely approximates this form. The charge variance can be measured by counting positive and negative singularities inside the region A, or more easily by counting signed zero crossings on the perimeter of A. \For the first method the charge variance is calculated by integration over the charge correlation function C(r), for the second by integration over the zero crossing correlation function Gamma(r). Using the explicit forms of C(r) and of Gamma(r) we show that both methods of calculation yield the same result. We show that for short range screening the zero crossings can be counted along a straight line whose length equals P, but that for long range screening this simplification no longer holds. We also show that for realizable optical fields, for sufficiently small R, the charge variance goes as R^2, whereas for sufficiently large R, it grows as R. These universal laws are applicable to both short and pseudo-long range correlation functions

Metal-superconductor transition at zero temperature: A case of unusual scaling

An effective field theory is derived for the normal metal-to-superconductor quantum phase transition at T=0. The critical behavior is determined exactly for all dimensions d>2. Although the critical exponents \beta and \nu do not exist, the usual scaling relations, properly reinterpreted, still hold. A complete scaling description of the transition is given, and the physics underlying the unusual critical behavior is discussed. Quenched disorder leads to anomalously strong T_c-fluctuations which are shown to explain the experimentally observed broadening of the transition in low-T_c thin films.Comment: 4 pp., no figs, final version as publishe

Evolution of the universality class in slightly diluted (1>p>0.8) Ising systems

The crossover of a pure (undiluted) Ising system (spin per site probability p=1) to a diluted Ising system (spin per site probability p<0.8) is studied by means of Monte Carlo calculations with p ranging between 1 and 0.8 at intervals of 0.025. The evolution of the self averaging is analyzed by direct determination of the normalized square widths for magnetization and susceptibility as a function of p. We find a monotonous and smooth evolution from the pure to the randomly diluted universality class. The p-dependent transition is found to be independent of the size (L). This property is very convenient for extrapolation towards the randomly diluted universality class avoiding complications resulting from finite size effects.Comment: 15 pages, 6 figures, RevTe

Dynamical properties of the Landau-Ginzburg model with long-range correlated quenched impurities

We investigate the critical dynamics of the time-dependent Landau-Ginzburg model with non conserved n-component order parameter (Model A) in the presence of long-range correlated quenched impurities. We use a special kind of long-range correlations, previously introduced by Weinrib and Halperin. Using a double expansion in \epsilon and \delta we calculate the critical exponent z up to second order on the small parameters. We show that the quenched impurities of this kind affect the critical dynamics already in first order of \epsilon and \delta, leading to a relevant correction for the mean field value of the exponent zComment: 7 pages, REVTEX, to be published in Phys. Rev.

The Academic Profession in Canada: Perceptions of Canadian University Faculty about Research and Teaching

Previous scholarly attention to the experiences of faculty members has emphasized the contexts of US institutions, with minimal attention to the experiences of faculty members at Canadian universities.&nbsp; This paper presents the findings of the Canadian component of an international survey that was administered in 19 different jurisdictions to understand the perceptions of faculty members about the nature and scope of changes to academic work. As such, the paper explores the perceptions on research and teaching of full-time faculty members affiliated with Canadian universities. Overall, faculty members revealed that Canadian universities have strong, engaging, and vibrant research and teaching environments, yet there are also areas for improvement. Specifically, findings showed that faculty members perceived considerable autonomy with respect to research activities, despite the increasing need to secure external funding for research. Also, faculty expressed substantial commitment to teaching undergraduate students but a lack of clarity about some issues related to graduate teaching. The survey results provide an important baseline for future studies of Canadian universities and the working conditions of the professoriate in a time of rapid institutional and professional change. &nbsp;Jusqu’à présent, les études scientifiques sur l’expérience du corps professoral ont surtout porté sur le contexte étatsunien, accordant très peu d’attention à l’expérience vécue dans les universités canadiennes. Cet article présente les résultats de la partie canadienne d’un sondage international effectué dans 19 juridictions, et dont le but était de comprendre la perception du corps professoral envers la nature et la portée de changements modifiant le travail académique. Dans l’ensemble, les membres du corps professoral ont confié que le milieu de la recherche et de l’enseignement est solide, stimulant et dynamique, bien que des points restent à améliorer. Plus précisément, notre recherche révèle que les membres du corps professoral perçoivent une autonomie considérable sur le plan des activités de recherche, malgré le besoin grandissant d’obtenir du financement externe pour la recherche. De plus, les membres du corps professoral ont exprimé leur engagement capital envers l’enseignement au premier cycle, mais aussi un manque de clarté quant à certains problèmes liés à l’enseignement aux cycles supérieurs. Dans un contexte de changements institutionnels et professionnels rapides, les résultats du sondage fournissent un important point de départ pour de futures études sur les universités canadiennes et les conditions de travail du corps professoral

Explicit Renormalization Group for D=2 random bond Ising model with long-range correlated disorder

We investigate the explicit renormalization group for fermionic field theoretic representation of two-dimensional random bond Ising model with long-range correlated disorder. We show that a new fixed point appears by introducing a long-range correlated disorder. Such as the one has been observed in previous works for the bosonic ($\phi^4$) description. We have calculated the correlation length exponent and the anomalous scaling dimension of fermionic fields at this fixed point. Our results are in agreement with the extended Harris criterion derived by Weinrib and Halperin.Comment: 5 page