Optical gyrotropy, the lifting of degeneracy between left and right\ncircularly polarized light, can be generated by either time-reversal or chiral\nsymmetry breaking. In the high-$T_c$ superconductor La$_{2-x}$Ba$_x$CuO$_4$\n(LBCO), gyrotropy onsets at the same temperature as charge stripe order,\nsuggesting that the rotation of the stripe direction from one plane to the next\ngenerates a helical pattern that breaks chiral symmetry. In order to further\ntest this chiral stacking hypothesis it is necessary to develop an\nunderstanding of the physical mechanism by which chirality generates gyrotropy.\nIn this paper we show that optical gyrotropy is a consequence of Berry\ncurvature in the momentum space of chiral metals. We describe a physical\npicture showing that gyrotropy in chiral metals is closely related to the\nanomalous Hall effect in itinerant ferromagnets. We then calculate the\nmagnitude of the gyrotropic response for a given Berry curvature using the\nsemiclassical picture of anomalous velocity and Boltzmann transport theory. To\nconnect this physical picture with experiment, we calculate the Berry curvature\nin two tight-binding models. The first model is motivated by the structure of\nLBCO and illustrates how the gyrotropy is created when the stripe perturbations\nare added to a simple cubic model. In the second model, we examine the dramatic\nenhancement of the gyrotropic coefficient when Rashba spin-orbit coupling is\nintroduced. The magnitude of the rotation of polarization on reflection\nexpected based these models is calculated and compared with experimental data.\n
Several methods for estimating surface energy balance components over a vegetated surface are compared. These include Penman-Monteith, Deardorff, and multilayer canopy (CANWHT) models for evaporation. Measurements taken during the 1991 DOE-sponsored Boardman Area Regional Flux Experiment over a Well-irrigated, closed wheat canopy are used in the comparison. The relative performance of each model is then evaluated. It is found that the Penman-Monteith approach using a simple parameterization for stomatal conductance performs best for evaporation flux. The Deardorff model is found to have the best relative performance for sensible heat, while the CANWHT model gives the best results for net radiation and soil heat flux. The Priestley-Taylor model for evaporation and a resistance-analog equation for sensible heat flux are also tested.
Distinguishing between two different schools of thought that are named after two different universities, Harvard and Berkeley, the article looks at the evolution, past and future, of the international monetary system. While the empirical view holds that the system will remain unipolar and dollar-based, the opposing view uses history to contend that it may potenially evolve away from the dollar into a multipolar system.
This paper gives sufficient conditions for an array of linearly coupled systems to synchronize. A typical result states that the array will synchronize if the nonzero eigenvalues of the coupling matrix have real parts that are negative enough. In particular, we show that the intuitive idea that strong enough mutual diffusive coupling will synchronize an array of identical cells is true in general. Sufficient conditions for synchronization for several coupling configurations will be considered. For coupling that leaves the array decoupled at the synchronized state, the cells each follow their natural uncoupled dynamics at the synchronized state. We illustrate this with an array of chaotic oscillators. Extensions of these results to general coupling are discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTCatalytic steam gasification of coalsP. Pereira, G. A. Somorjai, and H. HeinemannCite this: Energy Fuels 1992, 6, 4, 407–410Publication Date (Print):July 1, 1992Publication History Published online1 May 2002Published inissue 1 July 1992https://pubs.acs.org/doi/10.1021/ef00034a009https://doi.org/10.1021/ef00034a009research-articleACS PublicationsRequest reuse permissionsArticle Views352Altmetric-Citations23LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts
Mischungen von Cumarin-2- und Cumarin-343-Derivaten können sich auf einem Siliciumwafer zu Monoschichten selbstorganisieren, in denen Licht gesammelt und ein Energietransfer stattfinden kann (siehe schematische Darstellung). Photophysikalische Eigenschaften wie Fluoreszenzlöschung des Donors und Fluoreszenzverstärkung lassen sich durch Änderung des Molverhältnisses von Donor- zu Acceptorchromophor auf der Oberfläche einstellen oder – unter Verwendung eines dendritischen Linkers – durch Erhöhung der Zahl der Cumarin-2-Chromophore am Donoradsorbat.
Several new classes of transition metal-catalyzed reactions of amines with the CC bond of acrylic acid derivatives were discovered using a high-throughput colorimetric assay. This assay is general for the reactions of primary and secondary alkylamines with acrylic acid derivatives, and the screening of potential catalysts using this assay revealed a number of different metal/ligand combinations that promote these hydroaminations. The colorimetric assay revealed catalysts for the addition of piperidine to methacrylonitrile, crotononitrile, ethyl crotonate, and ethyl methacrylate, as well as catalysts for reactions of butylamine and aniline with methacrylonitrile. A catalyst for the addition of aniline to crotononitrile at 100 °C was also discovered. The products of these reactions are basic building blocks for the synthesis of β-amino acids, amino alcohols, and diamines. These reactions may ultimately produce an enantioselective route to optically active difunctional materials from commodity reagents.
The effect of intracellular polyphosphate on the phosphate-starvation response in Escherichia coli was studied by genetically manipulating the intracellular polyphosphate levels and by performing phosphate shifts on the genetically engineered strains. Strains that produced large quantities of polyphosphate and were able to degrade it induced the phosphate-starvation response to a lesser extent than wild-type strains, whereas strains that were unable to degrade a large intracellular polyphosphate pool induced the phosphate-starvation response to a greater extent than wild-type strains. These results have important implications for expression of heterologous genes under control of the phoA promoter. (c) 1996 John Wiley & Sons, Inc.
Campylobacter coli VC167 has been shown to undergo a reversible flagellar antigenic variation between antigenic type 1 (T1) and antigenic type 2 (T2). VC167 contains two flagellin genes, and the products of both genes are incorporated into a complex flagellar filament in both antigenic types. Although there are only minor amino acid changes in the flagellins expressed by T1 and T2 cells, the two antigenic types of flagellins can be distinguished by differences in apparent M(r) on sodium dodecyl sulfate-polyacrylamide gels and by immunoreactivity with T1-specific (LAH1) or T2-specific (LAH2) antiserum. The isolation of stable variants of T1 and T2 has allowed for the transfer via natural transformation of the flagellin structural genes from the T1 background into the T2 background and from the T2 background into the T1 background. In addition, the flagellin genes from VC167 T1 and T2 have been transferred into strains of Campylobacter jejuni. The results indicate that the observed antigenic variations of VC167 flagellins are dependent on the host genetic background and independent of the primary amino acid sequence. These data provide evidence that posttranslational modifications are responsible for the antigenic variation seen in VC167 flagellins.
We assemble an almost complete set of central bank statutes since 1800 to assess the legal independence of central banking institutions. We use these to extend existing indices of legal independence backward and forward in time. We document the trend toward increased independence post 1980 as well as an earlier, more limited movement in the direction of enhanced independence in the 1920s. We apply natural language processing to current statutes to corroborate our human-reader assessment. Using machine-learning methods, we quantify the extent to which topics in those statutes contribute to the independence measure based on our reading of the statutes. The topic with the largest positive contribution to explaining the cross-country variation in central bank independence encompasses disclosure, transparency, and reporting obligations. The topic with the largest negative contribution covers regulatory powers over inter alia securities markets that complicate the central bank's mandate, make accountability more complex, and render independence problematic.
Abstract A procedure based on rigorous non‐linear analysis is presented that estimates the peak deformation among all isolators in an asymmetric building due to strong ground motion. The governing equations are reduced to a form such that the median normalized deformation due to an ensemble of ground motions with given corner period T d depends primarily on four global parameters of the isolation system: the isolation period T b , the normalized strength η, the torsional‐to‐lateral frequency ratio Ω θ , and the normalized stiffness eccentricity e b /r . The median ratio of the deformations of the asymmetric and corresponding symmetric systems is shown to depend only weakly on T b , η, and Ω θ , but increases with e b /r . The equation developed to estimate the largest ratio among all isolators depends only on the stiffness eccentricity and the distance from the center of mass to the outlying isolator. This equation, multiplied by an earlier equation for the deformation of the corresponding symmetric system, provides a design equation to estimate the deformations of asymmetric systems. This design equation conservatively estimates the peak deformation among all isolators, but is generally within 10% of the ‘exact’ value. Relative to the non‐linear procedure presented, the peak isolator deformation is shown to be significantly underestimated by the U.S. building code procedures. Copyright © 2003 John Wiley & Sons, Ltd.
