Smoke-Free Policy in Vermont Public Housing Authorities

Introduction. Millions of adults and children living in public housing face exposure to second hand smoke from adjacent apartments. These tenants are less able to escape smoke exposure by moving, and Housing Authorities are beginning to implement smoke-free policies. We assessed the status of smoke-free policy in Vermont public housing, and explored the experience of tenants and managers in Burlington who recently implemented such a policy.https://scholarworks.uvm.edu/comphp_gallery/1080/thumbnail.jp

Crossover from 2-dimensional to 1-dimensional collective pinning in NbSe3

We have fabricated NbSe$_3$ structures with widths comparable to the Fukuyama-Lee-Rice phase-coherence length. For samples already in the 2-dimensional pinning limit, we observe a crossover from 2-dimensional to 1-dimensional collective pinning when the crystal width is less than 1.6 $\mu$m, corresponding to the phase-coherence length in this direction. Our results show that surface pinning is negligible in our samples, and provide a means to probe the dynamics of single domains giving access to a new regime in charge-density wave physics.Comment: 4 pages, 2 figures, and 1 table. Accepted for publication in Physical Review

Many-body Theory vs Simulations for the pseudogap in the Hubbard model

The opening of a critical-fluctuation induced pseudogap (or precursor pseudogap) in the one-particle spectral weight of the half-filled two-dimensional Hubbard model is discussed. This pseudogap, appearing in our Monte Carlo simulations, may be obtained from many-body techniques that use Green functions and vertex corrections that are at the same level of approximation. Self-consistent theories of the Eliashberg type (such as the Fluctuation Exchange Approximation) use renormalized Green functions and bare vertices in a context where there is no Migdal theorem. They do not find the pseudogap, in quantitative and qualitative disagreement with simulations, suggesting these methods are inadequate for this problem. Differences between precursor pseudogaps and strong-coupling pseudogaps are also discussed.Comment: Accepted, Phys. Rev. B15 15Mar00. Expanded version of original submission, Latex, 8 pages, epsfig, 5 eps figures (Last one new). Discussion on fluctuation and strong coupling induced pseudogaps expande

Temporally ordered collective creep and dynamic transition in the charge-density-wave conductor NbSe3

We have observed an unusual form of creep at low temperatures in the charge-density-wave (CDW) conductor NbSe$_3$. This creep develops when CDW motion becomes limited by thermally-activated phase advance past individual impurities, demonstrating the importance of local pinning and related short-length-scale dynamics. Unlike in vortex lattices, elastic collective dynamics on longer length scales results in temporally ordered motion and a finite threshold field. A first-order dynamic phase transition from creep to high-velocity sliding produces "switching" in the velocity-field characteristic.Comment: 4 pages, 4 eps figures; minor clarifications To be published in Phys. Rev. Let

Convective Term and Transversely Driven Charge-Density Waves

We derive the convective terms in the damping which determine the structure of the moving charge-density wave (CDW), and study the effect of a current flowing transverse to conducting chains on the CDW dynamics along the chains. In contrast to a recent prediction we find that the effect is orders of magnitude smaller, and that contributions from transverse currents of electron- and hole-like quasiparticles to the force exerted on the CDW along the chains act in the opposite directions. We discuss recent experimental verification of the effect and demonstrate experimentally that geometry effects might mimic the transverse current effect.Comment: RevTeX, 9 pages, 1 figure, accepted for publications in PR

Salt marsh ecosystem biogeochemical responses to nutrient enrichment : a paired 15N tracer study

Author Posting. © Ecological Society of America, 2009. This article is posted here by permission of Ecological Society of America for personal use, not for redistribution. The definitive version was published in Ecology 90 (2009): 2535-2546, doi:10.1890/08-1051.1.We compared processing and fate of dissolved NO3− in two New England salt marsh ecosystems, one receiving natural flood tide concentrations of 1–4 μmol NO3−/L and the other receiving experimentally fertilized flood tides containing 70–100 μmol NO3−/L. We conducted simultaneous 15NO3− (isotope) tracer additions from 23 to 28 July 2005 in the reference (8.4 ha) and fertilized (12.4 ha) systems to compare N dynamics and fate. Two full tidal cycles were intensively studied during the paired tracer additions. Resulting mass balances showed that essentially 100% (0.48–0.61 mol NO3-N·ha−1·h−1) of incoming NO3− was assimilated, dissimilated, sorbed, or sedimented (processed) within a few hours in the reference system when NO3− concentrations were 1.3–1.8 μmol/L. In contrast, only 50–60% of incoming NO3− was processed in the fertilized system when NO3− concentrations were 84–96 μmol/L; the remainder was exported in ebb tidewater. Gross NO3− processing was 40 times higher in the fertilized system at 19.34–24.67 mol NO3-N·ha−1·h−1. Dissimilatory nitrate reduction to ammonium was evident in both systems during the first 48 h of the tracer additions but <1% of incoming 15NO3− was exported as 15NH4+. Nitrification rates calculated by 15NO3− dilution were 6.05 and 4.46 mol·ha−1·h−1 in the fertilized system but could not be accurately calculated in the reference system due to rapid (<4 h) NO3− turnover. Over the five-day paired tracer addition, sediments sequestered a small fraction of incoming NO3−, although the efficiency of sequestration was 3.8% in the reference system and 0.7% in the fertilized system. Gross sediment N sequestration rates were similar at 13.5 and 12.6 mol·ha−1·d−1, respectively. Macrophyte NO3− uptake efficiency, based on tracer incorporation in aboveground tissues, was considerably higher in the reference system (16.8%) than the fertilized system (2.6%), although bulk uptake of NO3− by plants was lower in the reference system (1.75 mol NO3−·ha−1·d−1) than the fertilized system (10 mol NO3−·ha−1·d−1). Nitrogen processing efficiency decreased with NO3− load in all pools, suggesting that the nutrient processing capacity of the marsh ecosystem was exceeded in the fertilized marsh.This work was funded by National Science Foundation Grant DEB 0213767 and OCE 9726921

Defects, order, and hysteresis in driven charge-density waves

We model driven two-dimensional charge-density waves in random media via a modified Swift-Hohenberg equation, which includes both amplitude and phase fluctuations of the condensate. As the driving force is increased, we find that the defect density first increases and then decreases. Furthermore, we find switching phenomena, due to the formation of channels of dislocations. These results are in qualitative accord with recent dynamical x-ray scattering experiments by Ringlandet al. and transport experiments by Lemay et al.Comment: Accepted to Phys. Rev. Lett. Click here for "http://www-theory.mpip-mainz.mpg.de/~karttune/CDW/", movies of driven CDW

Understanding the errors of SHAPE-directed RNA structure modeling

Single-nucleotide-resolution chemical mapping for structured RNA is being rapidly advanced by new chemistries, faster readouts, and coupling to computational algorithms. Recent tests have shown that selective 2'-hydroxyl acylation by primer extension (SHAPE) can give near-zero error rates (0-2%) in modeling the helices of RNA secondary structure. Here, we benchmark the method using six molecules for which crystallographic data are available: tRNA(phe) and 5S rRNA from Escherichia coli, the P4-P6 domain of the Tetrahymena group I ribozyme, and ligand-bound domains from riboswitches for adenine, cyclic di-GMP, and glycine. SHAPE-directed modeling of these highly structured RNAs gave an overall false negative rate (FNR) of 17% and a false discovery rate (FDR) of 21%, with at least one helix prediction error in five of the six cases. Extensive variations of data processing, normalization, and modeling parameters did not significantly mitigate modeling errors. Only one varation, filtering out data collected with deoxyinosine triphosphate during primer extension, gave a modest improvement (FNR = 12%, and FDR = 14%). The residual structure modeling errors are explained by the insufficient information content of these RNAs' SHAPE data, as evaluated by a nonparametric bootstrapping analysis. Beyond these benchmark cases, bootstrapping suggests a low level of confidence (<50%) in the majority of helices in a previously proposed SHAPE-directed model for the HIV-1 RNA genome. Thus, SHAPE-directed RNA modeling is not always unambiguous, and helix-by-helix confidence estimates, as described herein, may be critical for interpreting results from this powerful methodology.Comment: Biochemistry, Article ASAP (Aug. 15, 2011

Noise Stabilization of Self-Organized Memories

We investigate a nonlinear dynamical system which ``remembers'' preselected values of a system parameter. The deterministic version of the system can encode many parameter values during a transient period, but in the limit of long times, almost all of them are forgotten. Here we show that a certain type of stochastic noise can stabilize multiple memories, enabling many parameter values to be encoded permanently. We present analytic results that provide insight both into the memory formation and into the noise-induced memory stabilization. The relevance of our results to experiments on the charge-density wave material $NbSe_3$ is discussed.Comment: 29 pages, 6 figures, submitted to Physical Review