4,587 research outputs found
Mediation of Long Range Charge Transfer by Kondo Bound States
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 10, 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
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
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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