1,178 research outputs found

    Exact renormalization group equation in presence of rescaling anomaly

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    Wilson's approach to renormalization group is reanalyzed for supersymmetric Yang-Mills theory. Usual demonstration of exact renormalization group equation must be modified due to the presence of the so called Konishi anomaly under the rescaling of superfields. We carry out the explicit computation for N=1 SUSY Yang-Mills theory with the simpler, gauge invariant regularization method, recently proposed by Arkani-Hamed and Murayama. The result is that the Wilsonian action S_M consists of two terms, i.e. the non anomalous term, which obeys Polchinski's flow equation and Fujikawa-Konishi determinant contribution. This latter is responsible for Shifman-Vainshtein relation of exact beta-function.Comment: 19 pages, no figures; an appendix and reference added; typos correcte

    Bio-logic: gene expression and the laws of combinatorial logic

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    Original article can be found at: http://www.mitpressjournals.org/ Copyright MIT Press DOI: 10.1162/artl.2008.14.1.121At the heart of the development of fertilized eggs into fully formed organisms and the adaptation of cells to changed conditions are genetic regulatory networks (GRNs). In higher multi-cellular organisms, signal selection and multiplexing is performed at the cis-regulatory domains of genes, where combinations of transcription factors (TFs) regulate the rates at which the genes are transcribed into mRNA. To be able to act as activators or repressors of gene transcription, TFs must first bind to target sequences on the regulatory domains. Two TFs that act in concert may bind entirely independently of each other, but more often binding of the first one will alter the affinity of the other for its binding site. This paper presents a systematic investigation into the effect of TF binding dependencies on the predicted regulatory function of this “bio-logic”. Four extreme scenarios, commonly used to classify enzyme activation and inhibition patterns, for the binding of two TFs were explored: independent (the TFs bind without affecting each other’s affinities), competitive (the TFs compete for the same binding site), ordered (the TFs bind in a compulsory order), and joint binding (the TFs either bind as a preformed complex, or binding of one is virtually impossible in the absence of the other). The conclusions are: 1) the laws of combinatorial logic hold only for systems with independently binding TFs; 2) systems formed according to the other scenarios can mimic the functions of their Boolean logical counterparts, but cannot be combined or decomposed in the same way; and 3) the continuously scaled output of systems consisting of competitively binding activators and repressors can be more robustly controlled than that of single TF or (quasi-) logical multi-TF systems. Keywords: Transcription regulation, Genetic regulatory networks, Enzyme kinetics, Combinatorial logic, Non-Boolean continuous logic, Modelling.Peer reviewe

    On the construction of QED using ERG

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    It has been known for some time that a smooth momentum cutoff is compatible with local gauge symmetries. In this paper we show concretely how to construct QED using the exact renormalization group (ERG). First, we give a new derivation of the Ward identity for the Wilson action using the technique of composite operators. Second, parameterizing the theory by its asymptotic behavior for a large cutoff, we show how to fine-tune the parameters to satisfy the identity. Third, we recast the identity as invariance of the Wilson action under a non-linear BRST transformation.Comment: 18 pages, LaTeX2e; added appendix A to improve sects. 2 and 4; added ref. 1

    A coupled stability and eco-hydrological model to predict shallow landslides

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    Knowledge of spatio-temporal dynamics of soil water content, groundwater and infiltration processes is of considerable importance for the understanding and prediction of landslides. Rainfall and consequent water infiltration affect slope stability in various ways, mainly acting on the pore pressure distribution whose increase causes a decrease of the shearing resistance of the soil. For such reasons rainfall and transient changes in the hydrological systems are considered the most common triggers of landslides. So far, the difficulty to monitor groundwater levels or soil moisture contents in unstable terrain have made modeling of landslide a complex issue. At the present, the availability of sophisticated hydrological and physically based models, able to simulate the main hydrological processes, has allowed the development of coupled hydrologicalstability models able to predict when and where a failure could occur. In this study, a slope-failure module, with capability to predict shallow landslides, implemented into an ecohydrological model, tRIBS-VEGGIE (Triangulated Irregular Network (TIN)-based Real-time Integrated Basin Simulator with VEGetation Generator for Interactive Evolution), is presented. The model evaluates the stability dynamics in term of factor of safety consequent to the soil moisture dynamics, strictly depending on the textural soil characteristics and hillslope geometry. Failure criterion used to derive factor of safety equation accounts for the stabilizing effect of matric suction arising in unsaturated soils. The eco-hydrological framework allows also to take into account the effect of vegetation with its cohesive effect as well as its weight load. The Mameyes basin, located in the Luquillo Experimental Forest in Puerto Rico, has been selected for modeling based on the availability of soil, vegetation, topographical, meteorological and historic landslide data. A static analysis based on susceptibility mapping approach was also carried out on the same area at a larger spatial scale, providing the hot spot of landsliding area. Application of the model yields a temporal and spatial distribution of predicted rainfall-induced landslides. Moreover, stability dynamics have been assessed for different meteorological forcing and soil types, to better evaluate the influence of hydrological dynamics on slope stability

    Agricultural Trade Liberalization and Capital Flows in the Americas

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    In the second of three related papers, the authors develop a model that estimates the effects on prices, outputs, and trade flows arising from the elimination of U.S. import tariffs on contemplate agricultural commodities from Latin America. Eight agricultural commodities and six countries were selected for analysis. The authors also assess how the increased trade flows from Latin America to the United States are likely to create additional investment in the agricultural sector in Latin American countries

    A Dynamic Comparative Advantage Analysis of Fresh Fruit and Vegetable Trade Between Latin America and the United States

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    In the first of three related papers, the authors analyze the dynamic pattern of comparative advantage in fruit and vegetable trade flows between the United States and Latin America. Their examination of several factors--including market demand, improving investment climates, technological advances, and trade liberalization--indicates a significant potential for the development and expansion of trade flows to meet open windows of opportunity in the United States

    Fabrication and Characterization of Polymeric Optical Waveguides Using Standard Silicon Processing Technology

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    We report the fabrication and characterization of a rib polymeric waveguide having a thick layer of oxidized porous silicon as an innovative solution for the lower cladding. The waveguide was fabricated using standard silicon substrates and Si-based technology. The multimodal guiding structure has a polymethylmetacrylate (PMMA) core and the innovative lower cladding was obtained by thermal oxidation of a porous silicon layer. The waveguide does not have the upper cladding. Propagation loss measurements were performed at 1.48 \u3bcm using the cut-back method. We obtained propagation loss of about 1.7 dB/cm, confirming the possibility to use the porous silicon oxide as the lower cladding layer, for low cost waveguide applications

    Institutional Rules and Mechanisms for Western Hemisphere Trade

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    In the third of three related papers, the authors discuss rules and mechanisms that could facilitate the expansion of the North American Free Trade Agreement (NAFTA) and promote freer trade and investment in the Americas. These mechanisms include macroeconomic policies that open trade and capital flows, and institutional policies that specify standards and requirements to protect investments and lower risks
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