4,587 research outputs found

    Mediation of Long Range Charge Transfer by Kondo Bound States

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    We present a theory of non-equilibrium long range charge transfer between donor and acceptor centers in a model polymer mediated by magnetic exciton (Kondo) bound states. Our model produces electron tunneling lengths easily exceeding 10A˚\AA, as observed recently in DNA and organic charge transfer systems. This long ranged tunneling is effective for weak to intermediate donor-bridge coupling, and is enhanced both by weak to intermediate strength Coulomb hole-electron attraction (through the orthogonality catastrophe) and by coupling to local vibrational modes.Comment: Revised content (broadened scope, vibrations added), submitted to Phys Rev Lett, added autho

    Optical conductivity of wet DNA

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    Motivated by recent experiments we have studied the optical conductivity of DNA in its natural environment containing water molecules and counter ions. Our density functional theory calculations (using SIESTA) for four base pair B-DNA with order 250 surrounding water molecules suggest a thermally activated doping of the DNA by water states which generically leads to an electronic contribution to low-frequency absorption. The main contributions to the doping result from water near DNA ends, breaks, or nicks and are thus potentially associated with temporal or structural defects in the DNA.Comment: 4 pages, 4 figures included, final version, accepted for publication in Phys. Rev. Let

    United States Food Law Update: Moving Toward a More Balanced Food Regulatory Regime

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    For decades, the federal government has played a significant role in promoting healthy eating. In the early 1900s, the United States Department of Agriculture (USDA) promoted a foundational diet of milk, proteins, fruits and vegetables, and grains. Most Americans are at least somewhat familiar, although perhaps confused, with the more nuanced healthy eating recommendations contained in the food pyramid - first employed in 1992. And virtually every American has experienced the federally supported school lunch program. In the first half of 2011, these two iconic programs underwent significant change as part of a stepped-up effort to improve the health of the country through better food choices. Part I of this article describes the MyPlate initiative that replaces the iconic USDA food pyramid and menu revisions to the national school lunch and school breakfast programs. This section also profiles administrative decisions in two school districts to ban, on health grounds, brown- bag lunches in favor of school- provided lunches. Finally, this section describes some of the challenges of implementing a rule for chain restaurant menu labeling under the Patient Protection and Affordable Care Act
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