The Spectral Dimension of 2D Quantum Gravity

We show that the spectral dimension d_s of two-dimensional quantum gravity coupled to Gaussian fields is two for all values of the central charge c <= 1. The same arguments provide a simple proof of the known result d_s= 4/3 for branched polymers.Comment: 7 pages, Late

Some comments on the divergence of perturbation series in Quantum Eletrodynamics

It has been argued by Dyson that the perturbation series in coupling constant in QED can not be convergent. We find that similiar albeit slightly different arguments lead to the divergence of the series of $1/N_f$ expansion in QED.Comment: Final Version, To appear in Modern Physics Letters

The Americanization of Karen Refugee Youth: Exploring Attitudes Toward and Use of Methamphetamine

Drug use among refugee populations is a concerning trend in many urban American cities. For instance, Omaha, Nebraska is home to an estimated 7,000 refugees from Myanmar, with at least 75% of those being Karen refugees. The purpose of this paper is to explore methamphetamine use among Karen adolescents in Omaha and to examine whether Karen youth bring their drug use habits with them from refugee camps or if they learn about drugs from their American peers. Two focus groups of Karen youth and two focus groups of Karen parents were conducted to examine methamphetamine use among this population. Findings suggest, like most youth, the Karen children were reluctant to disclose their own use of drugs, but they did see the use of methamphetamine and other drugs in their schools. It appears drug use among the Karen youth is acquired during the “Americanization” of these children in Omaha schools

Microscopic theory of glassy dynamics and glass transition for molecular crystals

We derive a microscopic equation of motion for the dynamical orientational correlators of molecular crystals. Our approach is based upon mode coupling theory. Compared to liquids we find four main differences: (i) the memory kernel contains Umklapp processes, (ii) besides the static two-molecule orientational correlators one also needs the static one-molecule orientational density as an input, where the latter is nontrivial, (iii) the static orientational current density correlator does contribute an anisotropic, inertia-independent part to the memory kernel, (iv) if the molecules are assumed to be fixed on a rigid lattice, the tensorial orientational correlators and the memory kernel have vanishing l,l'=0 components. The resulting mode coupling equations are solved for hard ellipsoids of revolution on a rigid sc-lattice. Using the static orientational correlators from Percus-Yevick theory we find an ideal glass transition generated due to precursors of orientational order which depend on X and p, the aspect ratio and packing fraction of the ellipsoids. The glass formation of oblate ellipsoids is enhanced compared to that for prolate ones. For oblate ellipsoids with X <~ 0.7 and prolate ellipsoids with X >~ 4, the critical diagonal nonergodicity parameters in reciprocal space exhibit more or less sharp maxima at the zone center with very small values elsewhere, while for prolate ellipsoids with 2 <~ X <~ 2.5 we have maxima at the zone edge. The off-diagonal nonergodicity parameters are not restricted to positive values and show similar behavior. For 0.7 <~ X <~ 2, no glass transition is found. In the glass phase, the nonergodicity parameters show a pronounced q-dependence.Comment: 17 pages, 12 figures, accepted at Phys. Rev. E. v4 is almost identical to the final paper version. It includes, compared to former versions v2/v3, no new physical content, but only some corrected formulas in the appendices and corrected typos in text. In comparison to version v1, in v2-v4 some new results have been included and text has been change

Variational bound on energy dissipation in turbulent shear flow

We present numerical solutions to the extended Doering-Constantin variational principle for upper bounds on the energy dissipation rate in plane Couette flow, bridging the entire range from low to asymptotically high Reynolds numbers. Our variational bound exhibits structure, namely a pronounced minimum at intermediate Reynolds numbers, and recovers the Busse bound in the asymptotic regime. The most notable feature is a bifurcation of the minimizing wavenumbers, giving rise to simple scaling of the optimized variational parameters, and of the upper bound, with the Reynolds number.Comment: 4 pages, RevTeX, 5 postscript figures are available as one .tar.gz file from [email protected]

The regulated four parameter one dimensional point interaction

The general four parameter point interaction in one dimensional quantum mechanics is regulated. It allows the exact solution, but not the perturbative one. We conjecture that this is due to the interaction not being asymptotically free. We then propose a different breakup of unperturbed theory and interaction, which now is asymptotically free but leads to the same physics. The corresponding regulated potential can be solved both exactly and perturbatively, in agreement with the conjecture.Comment: 17 pages, no figures, Tex fil

Failing Homeostasis of Quadriceps Muscle Energy- and pH Balance During Bicycling in a Young Patient With a Fontan Circulation

Aims: Patients with a congenital heart condition palliated with a Fontan circulation generally present with decreased exercise capacity due to impaired cardiopulmonary function. Recently, a study in patients with a Fontan circulation reported evidence for abnormal vascular endothelial function in legmuscle. We investigated if abnormal skeletal muscle hemodynamics during exercise play a role in the limited exercise tolerance of Fontan patients. If so, abnormalities in intramuscular energy metabolism would be expected both during exercise as well as during post-exercise metabolic recovery. Methods: In a young patient with a Fontan circulation and his healthy twin brother we studied the in vivo dynamics of energy-and pH-balance in quadriceps muscle during and after a maximal in-magnet bicycling exercise challenge using 31-phosphorus magnetic resonance spectroscopy. An unrelated age-matched boy was also included as independent control. Results: Quadriceps phosphocreatine (PCr) depletion during progressive exercise was more extensive in the Fontan patient than in both controls (95% vs. 80%, respectively). Importantly, it failed to reach an intermittent plateau phase observed in both controls. Quadriceps pH during exercise in the Fontan patient fell 0.3 units at low to moderate workloads, dropping to pH 6.6 at exhaustion. In both controls quadriceps acidification during exercise was absent but for the maximal workload in the twin brother (pH 6.8). Post-exercise, the rate of metabolic recovery in the Fontan patient and both controls was identical (time constant of PCr recovery 32 +/- 4, 31 +/- 2, and 28 +/- 4 s, respectively). Conclusion: Homeostasis of quadriceps energy- and pH-balance during a maximal exercise test failed in the Fontan patient in comparison to his healthy twin brother and an age-matched independent control. Post-exercise metabolic recovery was normal which does not support the contribution of significant endothelial dysfunction affecting adequate delivery of oxidative substrates to the muscle to the lower exercise capacity in this particular Fontan patient. These results suggest that mitochondrial ATP synthetic capacity of the quadriceps muscle was intact but cardiac output to the leg muscles during exercise was insufficient to meet the muscular demand for oxygen. Therefore, improving cardiac output remains the main therapeutic target to improve exercise capacity in patients with a Fontan circulation

Gravitational Waves from Axisymmetric, Rotational Stellar Core Collapse

We have carried out an extensive set of two-dimensional, axisymmetric, purely-hydrodynamic calculations of rotational stellar core collapse with a realistic, finite-temperature nuclear equation of state and realistic massive star progenitor models. For each of the total number of 72 different simulations we performed, the gravitational wave signature was extracted via the quadrupole formula in the slow-motion, weak-field approximation. We investigate the consequences of variation in the initial ratio of rotational kinetic energy to gravitational potential energy and in the initial degree of differential rotation. Furthermore, we include in our model suite progenitors from recent evolutionary calculations that take into account the effects of rotation and magnetic torques. For each model, we calculate gravitational radiation wave forms, characteristic wave strain spectra, energy spectra, final rotational profiles, and total radiated energy. In addition, we compare our model signals with the anticipated sensitivities of the 1st- and 2nd-generation LIGO detectors coming on line. We find that most of our models are detectable by LIGO from anywhere in the Milky Way.Comment: 13 pages, 22 figures, accepted for publication in ApJ (v600, Jan. 2004). Revised version: Corrected typos and minor mistakes in text and references. Minor additions to the text according to the referee's suggestions, conclusions unchange

Dectin-1 plays a redundant role in the immunomodulatory activities of β-glucan-rich ligands in vivo

Copyright © 2013 Institut Pasteur. Published by Elsevier Masson SAS. All rights reserved.Peer reviewedPublisher PD

Discovery and quantitative spectral analysis of an Ofpe/WN9 (WN11) star in the Sculptor spiral galaxy NGC 300

We have discovered an Ofpe/WN9 (WN11 following Smith et al.) star in the Sculptor spiral galaxy NGC 300, the first object of this class found outside the Local Group, during a recent spectroscopic survey of blue supergiant stars obtained at the ESO VLT. The light curve over a five-month period in late 1999 displays a variability at the 0.1 mag level. The intermediate resolution spectra (3800-7200 A) show a very close resemblance to the Galactic LBV AG Car during minimum. We have performed a detailed non-LTE analysis of the stellar spectrum, and have derived a chemical abundance pattern which includes H, He, C, N, O, Al, Si and Fe, in addition to the stellar and wind parameters. The derived stellar properties and the He and N surface enrichments are consistent with those of other Local Group WN11 stars in the literature, suggesting a similar quiescent or post-LBV evolutionary status.Comment: 9 pages, 4 figures, 2 tables. Accepted for publication in the Astrophysical Journal Letter