A Model for Estimating Future Emissions of Sulfur Hexafluoride and Perfluorocarbons

Sulfur hexafluoride (SF6), perfluoromethane (CF4) and perfluoroethane (C2F6) are strong greenhouse gases with long atmospheric residence times. Under the Kyoto Protocol to the Framework Convention on Climate Change adopted in December 1997, industrialized nations agreed to regulate their emissions of these gases. Here we present a simple spreadsheet model that is useful for projecting future emissions and analyzing compliance with regulatory commitments. We use atmospheric measurements of these gases and engineering studies to derive emission factors and scenarios for each of the major anthropogenic sources (leakage from electrical equipment, magnesium casting, aluminum smelting and semiconductor fabrication). Our model is useful for policy analysis because it divides the world into regions of nations that correspond with the political coalitions that dominate the international negotiations through which regulatory commitments are adopted. We show that although firms in many industrialized countries are already limiting emissions, without further policy intervention global emissions will rise 150% (CF4 and C2F6) and 210% (SF6) between 1990 to 2050; radiative forcing will increase 0.026 W m-2. Full application of available low- and negative-cost policies in industrialized nations would cut that radiative forcing by one-quarter. We also quantify plausible future manipulations to governmental data and show their possible effect on compliance with the targets of the Kyoto Protocol. West European nations can "cut" their emissions of these gases by half by 2010 simply by manipulating emission factors within the current bounds of uncertainty. The need for more complete and transparent data on these gases is urgent

Role of disorder in half-filled high Landau levels

We study the effects of disorder on the quantum Hall stripe phases in half-filled high Landau levels using exact numerical diagonalization. We show that, in the presence of weak disorder, a compressible, striped charge density wave, becomes the true ground state. The projected electron density profile resembles that of a smectic liquid. With increasing disorder strength W, we find that there exists a critical value, W_c \sim 0.12 e^2/\epsilon l, where a transition/crossover to an isotropic phase with strong local electron density fluctuations takes place. The many-body density of states are qualitatively distinguishable in these two phases and help elucidate the nature of the transition.Comment: 4 pages, 4 figure

Perturbation theories for the S=1/2 spin ladder with four-spin ring exchange

The isotropic S=1/2 antiferromagnetic spin ladder with additional four-spin ring exchange is studied perturbatively in the strong coupling regime with the help of cluster expansion technique, and by means of bosonization in the weak coupling limit. It is found that a sufficiently large strength of ring exchange leads to a second-order phase transition, and the shape of the boundary in the vicinity of the known exact transition point is obtained. The critical exponent for the gap is found to be $\eta\simeq1$, in agreement both with exact results available for the dimer line and with the bosonization analysis. The phase emerging for high values of the ring exchange is argued to be gapped and spontaneously dimerized. The results for the transition line from strong coupling and from weak coupling match with each other naturally.Comment: 8 pages, 4 figures, some minor changes in text and reference

Quantum-Hall Quantum-Bits

Bilayer quantum Hall systems can form collective states in which electrons exhibit spontaneous interlayer phase coherence. We discuss the possibility of using bilayer quantum dot many-electron states with this property to create two-level systems that have potential advantages as quantum bits.Comment: 4 pages, 4 figures included, version to appear in Phys. Rev. B (Rapid Communications

Orbital and spin contributions to the gg-tensors in metal nanoparticles

We present a theoretical study of the mesoscopic fluctuations of $g$-tensors in a metal nanoparticle. The calculations were performed using a semi-realistic tight-binding model, which contains both spin and orbital contributions to the $g$-tensors. The results depend on the product of the spin-orbit scattering time $\tau_{\textrm{\small so}}$ and the mean-level spacing $\delta$, but are otherwise weakly affected by the specific shape of a {\it generic} nanoparticle. We find that the spin contribution to the $g$-tensors agrees with Random Matrix Theory (RMT) predictions. On the other hand, in the strong spin-orbit coupling limit $\delta \tau_{\textrm{\small so}}/\hbar \to 0$, the orbital contribution depends crucially on the space character of the quasi-particle wavefunctions: it levels off at a small value for states of $d$ character but is strongly enhanced for states of $sp$ character. Our numerical results demonstrate that when orbital coupling to the field is included, RMT predictions overestimate the typical $g$-factor of orbitals that have dominant $d$-character. This finding points to a possible source of the puzzling discrepancy between theory and experiment.Comment: 21 pages, 6 figures; accepted for publication in Physical Review

Mean-field Phase Diagram of Two-Dimensional Electrons with Disorder in a Weak Magnetic Field

We study two-dimensional interacting electrons in a weak perpendicular magnetic field with the filling factor $\nu \gg 1$ and in the presence of a quenched disorder. In the framework of the Hartree-Fock approximation, we obtain the mean-field phase diagram for the partially filled highest Landau level. We find that the CDW state can exist if the Landau level broadening $1/2\tau$ does not exceed the critical value $1/2\tau_{c}=0.038\omega_{H}$. Our analysis of weak crystallization corrections to the mean-field results shows that these corrections are of the order of $(1/\nu)^{2/3}\ll 1$ and therefore can be neglected

Interacting Electrons on a Fluctuating String

We consider the problem of interacting electrons constrained to move on a fluctuating one-dimensional string. An effective low-energy theory for the electrons is derived by integrating out the string degrees of freedom to lowest order in the inverse of the string tension and mass density, which are assumed to be large. We obtain expressions for the tunneling density of states, the spectral function and the optical conductivity of the system. Possible connections with the phenomenology of the cuprate high temperature superconductors are discussed.Comment: 14 pages, 1 figur

Theory of the Quantum Hall Smectic Phase II: Microscopic Theory

We present a microscopic derivation of the hydrodynamic theory of the Quantum Hall smectic or stripe phase of a two-dimensional electron gas in a large magnetic field. The effective action of the low energy is derived here from a microscopic picture by integrating out high energy excitations with a scale of the order the cyclotron energy.The remaining low-energy theory can be expressed in terms of two canonically conjugate sets of degrees of freedom: the displacement field, that describes the fluctuations of the shapes of the stripes, and the local charge fluctuations on each stripe.Comment: 20 pages, RevTex, 3 figures, second part of cond-mat/0105448 New and improved Introduction. Final version as it will appear in Physical Review

What is the fate of the river waters of Hudson Bay?

Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Journal of Marine Systems 88 (2011): 352-361, doi:10.1016/j.jmarsys.2011.02.004.We examine the freshwater balance of Hudson and James bays, two shallow and fresh seas that annually receive 12% of the pan- Arctic river runoff. The analyses use the results from a 3–D sea ice-ocean coupled model with realistic forcing for tides, rivers, ocean boundaries, precipitation, and winds. The model simulations show that the annual freshwater balance is essentially between the river input and a large outflow toward the Labrador shelf. River waters are seasonally exchanged from the nearshore region to the interior of the basin, and the volumes exchanged are substantial (of the same order of magnitude as the annual river input). This lateral exchange is mostly caused by Ekman transport, and its magnitude and variability are controlled by the curl of the stress at the surface of the basin. The average transit time of the river waters is 3.0 years, meaning that the outflow is a complex mixture of the runoff from the three preceding years.We thank NSERC and the Canada Research Chairs program for funding. FS acknowledges support from NSF OCE-0751554 and ONR N00014-08-10490

Partial anomalous pulmonary venous drainage in patients presenting with suspected pulmonary hypertension: A series of 90 patients from the ASPIRE registry

Background and objective There are limited data regarding patients with PAPVD with suspected and diagnosed PH. Methods Patients with PAPVD presenting to a large PH referral centre during 2007–2017 were identified from the ASPIRE registry. Results Ninety patients with PAPVD were identified; this was newly diagnosed at our unit in 71 patients (78%), despite 69% of these having previously undergone CT. Sixty‐seven percent had a single right superior and 23% a single left superior anomalous vein. Patients with an SV‐ASD had a significantly larger RV area, pulmonary artery and L‐R shunt and a higher % predicted DLCO (all P  3 WU. Seven of these patients had isolated PAPVD, five of whom (8% of those patients with PH) had anomalous drainage of a single pulmonary vein. Conclusion Undiagnosed PAPVD with or without ASD may be present in patients with suspected PH; cross‐sectional imaging should therefore be specifically assessed whenever this diagnosis is considered. Radiological and physiological markers of L‐R shunt are higher in patients with an associated SV‐ASD. Although many patients with PAPVD and PH may have other potential causes of PH, a proportion of patients diagnosed with PAH have isolated PAPVD in the absence of other causative conditions