Quantum oscillations of nitrogen atoms in uranium nitride

The vibrational excitations of crystalline solids corresponding to acoustic or optic one phonon modes appear as sharp features in measurements such as neutron spectroscopy. In contrast, many-phonon excitations generally produce a complicated, weak, and featureless response. Here we present time-of-flight neutron scattering measurements for the binary solid uranium nitride (UN), showing well-defined, equally-spaced, high energy vibrational modes in addition to the usual phonons. The spectrum is that of a single atom, isotropic quantum harmonic oscillator and characterizes independent motions of light nitrogen atoms, each found in an octahedral cage of heavy uranium atoms. This is an unexpected and beautiful experimental realization of one of the fundamental, exactly-solvable problems in quantum mechanics. There are also practical implications, as the oscillator modes must be accounted for in the design of generation IV nuclear reactors that plan to use UN as a fuel.Comment: 25 pages, 10 figures, submitted to Nature Communications, supplementary information adde

Shedding light on plant litter decomposition: Advances, implications and new directions in understanding the role of photodegradation

Litter decomposition contributes to one of the largest fluxes of carbon (C) in the terrestrial biosphere and is a primary control on nutrient cycling. The inability of models using climate and litter chemistry to predict decomposition in dry environments has stimulated investigation of non-traditional drivers of decomposition, including photodegradation, the abiotic decomposition of organic matter via exposure to solar radiation. Recent work in this developing field shows that photodegradation may substantially influence terrestrial C fluxes, including abiotic production of carbon dioxide, carbon monoxide and methane, especially in arid and semi-arid regions. Research has also produced contradictory results regarding controls on photodegradation. Here we summarize the state of knowledge about the role of photodegradation in litter decomposition and C cycling and investigate drivers of photodegradation across experiments using a meta-analysis. Overall, increasing litter exposure to solar radiation increased mass loss by 23% with large variation in photodegradation rates among and within ecosystems. This variation was tied to both litter and environmental characteristics. Photodegradation increased with litter C to nitrogen (N) ratio, but not with lignin content, suggesting that we do not yet fully understand the underlying mechanisms. Photodegradation also increased with factors that increased solar radiation exposure (latitude and litter area to mass ratio) and decreased with mean annual precipitation. The impact of photodegradation on C (and potentially N) cycling fundamentally reshapes our thinking of decomposition as a solely biological process and requires that we define the mechanisms driving photodegradation before we can accurately represent photodegradation in global C and N models. © 2012 US Government

Mechanism of copper(II)-induced misfolding of Parkinson's disease protein

α-synuclein (aS) is a natively unfolded pre-synaptic protein found in all Parkinson's disease patients as the major component of fibrillar plaques. Metal ions, and especially Cu(II), have been demonstrated to accelerate aggregation of aS into fibrillar plaques, the precursors to Lewy bodies. In this work, copper binding to aS is investigated by a combination of quantum and molecular mechanics simulations. Starting from the experimentally observed attachment site, several optimized structures of Cu-binding geometries are examined. The most energetically favorable attachment results in significant allosteric changes, making aS more susceptible to misfolding. Indeed, an inverse kinematics investigation of the configuration space uncovers a dynamically stable β-sheet conformation of Cu-aS that serves as a nucleation point for a second β-strand. Based on these findings, we propose an atomistic mechanism of copper-induced misfolding of aS as an initial event in the formation of Lewy bodies and thus in PD pathogenesis

The state of pediatric asthma in Chicago's Humboldt Park: a community-based study in two local elementary schools

Abstract Background Pediatric asthma is a serious public health problem in Chicago and has been designated a high priority concern by residents of Chicago's Humboldt Park, a diverse community area with a large number of Puerto Rican, African American, and Mexican American families. Methods In May 2009, following the principles of community-based participatory research, a cross-sectional asthma screening survey was administered to adult caregivers of children attending two Humboldt Park elementary schools. Data were analyzed to determine the prevalence of diagnosed and probable asthma as well as the degree of asthma control among affected children; associations between asthma outcomes and mutable triggers were evaluated. Results Surveys from 494 children were evaluated. Physician-diagnosed asthma was reported for 24.9% of children and probable asthma identified in an additional 16.2% of children. Asthma was poorly or moderately controlled in 60.0% of diagnosed children. Smoking occurred inside 25.0% of households and 75.0% of caregivers reported idling of vehicles in their community. Report of general stress among caregivers, stress due to community crime, and/or an inability to cope with everyday life were significantly and positively associated with poor asthma morbidity and control among affected children. Conclusions Despite high prevalence rates and poor asthma morbidity and control in Humboldt Park, the association of these measures with mutable variables is promising. A community-based asthma intervention to address the issues identified in this study is needed to affect positive change.http://deepblue.lib.umich.edu/bitstream/2027.42/112574/1/12887_2010_Article_357.pd

Oxidation behavior of graphene-coated copper at intrinsic graphene defects of different origins

The development of ultrathin barrier films is vital to the advanced semiconductor industry. Graphene appears to hold promise as a protective coating; however, the polycrystalline and defective nature of engineered graphene hinders its practical applications. Here, we investigate the oxidation behavior of graphene-coated Cu foils at intrinsic graphene defects of different origins. Macro-scale information regarding the spatial distribution and oxidation resistance of various graphene defects is readily obtained using optical and electron microscopies after the hot-plate annealing. The controlled oxidation experiments reveal that the degree of structural deficiency is strongly dependent on the origins of the structural defects, the crystallographic orientations of the underlying Cu grains, the growth conditions of graphene, and the kinetics of the graphene growth. The obtained experimental and theoretical results show that oxygen radicals, decomposed from water molecules in ambient air, are effectively inverted at Stone-Wales defects into the graphene/Cu interface with the assistance of facilitators