10,054 research outputs found

    Underperforming policy networks : the biopesticides network in the United Kingdom

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    Loosely integrated and incomplete policy networks have been neglected in the literature. They are important to consider in terms of understanding network underperformance. The effective delivery and formulation of policy requires networks that are not incomplete or underperforming. The biopesticides policy network in the United Kingdom is considered and its components identified with an emphasis on the lack of integration of retailers and environmental groups. The nature of the network constrains the actions of its agents and frustrates the achievement of policy goals. A study of this relatively immature policy network also allows for a focus on network formation. The state, via an external central government department, has been a key factor in the development of the network. Therefore, it is important to incorporate such factors more systematically into understandings of network formation. Feedback efforts from policy have increased interactions between productionist actors but the sphere of consumption remains insufficiently articulated

    Potential of Interplanetary Torques and Solar Modulation for Triggering Terrestrial Atmospheric and Lithospheric Events

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    The Sun is forced into an orbit around the barycenter of the solar system because of the changing mass distribution of the planets. Solar-planetary-lunar dynamic relationships may form a new basis for understanding and predicting cyclic solar forcing functions on the Earth's climate.Comment: Invited Paper at the Fourth UN/ESA Workshop on Basic Space Science, Cairo, Egypt, July 1994. 7 pages LaTeX. Accepted for publication in the journal Earth, Moon, and Planet

    Chitobiose utilization in Borrelia burgdorferi is dually regulated by RpoD and RpoS

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    <p>Abstract</p> <p>Background</p> <p><it>Borrelia burgdorferi </it>has limited biosynthetic capabilities and must scavenge N-acetylglucosamine (GlcNAc), an essential component of the microbial cell wall, from the surrounding environment. Spirochetes cultured in the absence of free GlcNAc exhibit biphasic growth; however, addition of chitobiose (a dimer of GlcNAc) substitutes for free GlcNAc resulting in a single exponential phase. We evaluated the effect of RpoS and RpoN, the only alternative sigma factors in <it>B. burgdorferi</it>, on biphasic growth and chitobiose utilization in the absence of free GlcNAc. In addition, we investigated the source of GlcNAc in the second exponential phase.</p> <p>Results</p> <p>By comparing the growth of wild-type cells to insertional mutants for <it>rpoS </it>and <it>rpoN </it>we determined that RpoS, but not RpoN, partially regulates both biphasic growth and chitobiose utilization. The <it>rpoS </it>mutant, cultured in the absence of free GlcNAc, exhibited a significant delay in the ability to initiate a second exponential phase compared to the wild type and <it>rpoS </it>complemented mutant. Expression analysis of <it>chbC</it>, which encodes the membrane-spanning protein of the chitobiose phosphotransferase system, suggests the delay is due to the inability of the <it>rpoS </it>mutant to up regulate <it>chbC</it>. Furthermore, supplementing GlcNAc starved cultures with high concentrations (75 or 150 μM) of chitobiose resulted in biphasic growth of the <it>rpoS </it>mutant compared to a single exponential phase for the wild type and <it>rpoS </it>complemented mutant. In contrast, growth of the <it>rpoN </it>mutant under all conditions was similar to the wild type. 5' Rapid amplification of cDNA ends (5' RACE) revealed the transcriptional start site for <it>chbC </it>to be 42 bp upstream of the translational start site. Analysis of the <it>chbC </it>promoter region revealed homology to previously described RpoD and RpoS <it>B. burgdorferi </it>promoters. We also determined that yeastolate, a component of the growth medium (BSK-II), is not essential for second exponential phase growth.</p> <p>Conclusion</p> <p>Together these results suggest that RpoD and RpoS, but not RpoN, regulate biphasic growth and chitobiose utilization in <it>B. burgdorferi </it>by regulating the expression of the chitobiose transporter (<it>chbC</it>). The data also demonstrate that the second exponential phase observed in wild-type cells in the absence of free GlcNAc is not due to free chitobiose or GlcNAc oligomers present in the medium.</p

    Competition among Sellers in Securities Auctions

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    We study simultaneous security-bid second-price auctions with competition among sellers for potential bidders. The sellers compete by designing ordered sets of securities that the bidders can offer as payment for the assets. Upon observing auction designs, potential bidders decide which auctions to enter. We characterize all symmetric equilibria and show that there always exist equilibria in which auctions are in standard securities or their combinations. In large markets the unique equilibrium is auctions in pure cash. We extend the model for competition in reserve prices and show that binding reserve prices never constitute equilibrium as long as equilibrium security designs are not call options. (JEL D44, D82, G10)

    The chitobiose transporter, chbC, is required for chitin utilization in Borrelia burgdorferi

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    <p>Abstract</p> <p>Background</p> <p>The bacterium <it>Borrelia burgdorferi</it>, the causative agent of Lyme disease, is a limited-genome organism that must obtain many of its biochemical building blocks, including N-acetylglucosamine (GlcNAc), from its tick or vertebrate host. GlcNAc can be imported into the cell as a monomer or dimer (chitobiose), and the annotation for several <it>B. burgdorferi </it>genes suggests that this organism may be able to degrade and utilize chitin, a polymer of GlcNAc. We investigated the ability of <it>B. burgdorferi </it>to utilize chitin in the absence of free GlcNAc, and we attempted to identify genes involved in the process. We also examined the role of RpoS, one of two alternative sigma factors present in <it>B. burgdorferi</it>, in the regulation of chitin utilization.</p> <p>Results</p> <p>Using fluorescent chitinase substrates, we demonstrated an inherent chitinase activity in rabbit serum, a component of the <it>B. burgdorferi </it>growth medium (BSK-II). After inactivating this activity by boiling, we showed that wild-type cells can utilize chitotriose, chitohexose or coarse chitin flakes in the presence of boiled serum and in the absence of free GlcNAc. Further, we replaced the serum component of BSK-II with a lipid extract and still observed growth on chitin substrates without free GlcNAc. In an attempt to knockout <it>B. burgdorferi </it>chitinase activity, we generated mutations in two genes (<it>bb0002 </it>and <it>bb0620</it>) predicted to encode enzymes that could potentially cleave the β-(1,4)-glycosidic linkages found in chitin. While these mutations had no effect on the ability to utilize chitin, a mutation in the gene encoding the chitobiose transporter (<it>bbb04</it>, <it>chbC</it>) did block utilization of chitin substrates by <it>B. burgdorferi</it>. Finally, we provide evidence that chitin utilization in an <it>rpoS </it>mutant is delayed compared to wild-type cells, indicating that RpoS may be involved in the regulation of chitin degradation by this organism.</p> <p>Conclusions</p> <p>The data collected in this study demonstrate that <it>B. burgdorferi </it>can utilize chitin as a source of GlcNAc in the absence of free GlcNAc, and suggest that chitin is cleaved into dimers before being imported across the cytoplasmic membrane via the chitobiose transporter. In addition, our data suggest that the enzyme(s) involved in chitin degradation are at least partially regulated by the alternative sigma factor RpoS.</p

    Lognormal scale invariant random measures

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    In this article, we consider the continuous analog of the celebrated Mandelbrot star equation with lognormal weights. Mandelbrot introduced this equation to characterize the law of multiplicative cascades. We show existence and uniqueness of measures satisfying the aforementioned continuous equation; these measures fall under the scope of the Gaussian multiplicative chaos theory developed by J.P. Kahane in 1985 (or possibly extensions of this theory). As a by product, we also obtain an explicit characterization of the covariance structure of these measures. We also prove that qualitative properties such as long-range independence or isotropy can be read off the equation.Comment: 31 pages; Probability Theory and Related Fields (2012) electronic versio
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