Missouri Research Reactor publications (MU)
Permanent URI for this collection
Items in this collection are scholarly publications made by University of Missouri Research Reactor Center faculty, staff, and students, either alone or as co-authors, and which may or may not have been published in an alternate format. Items may contain more than one file type.
Browse
Recent Submissions
Item Design of an Epidemiologic Study of Drinking Water Arsenic Exposure and Skin and Bladder Cancer Risk in a U.S. Population(National Institute of Environmental Health Sciences, 1999) Karagas, Margaret R.; Tosteson, Tor D.; Blum, Joel; Morris, Steve; Baron, John; Klaue, BjoernIngestion of arsenic-contaminated drinking water is associated with an increased risk of several cancers, including skin and bladder malignancies; but it is not yet clear whether such adverse effects are present at levels to which the U.S. population is exposed. In New Hampshire, detectable levels of arsenic have been reported in drinking water supplies throughout the state. Therefore, we have begun a population-based epidemiologic case-control study in which residents of New Hampshire diagnosed with primary squamous cell (n=900) and basal cell (n=1200) skin cancers are being selected from a special statewide skin cancer incidence survey ; patients diagnosed with primary bladder cancers (n=450) are being identified through the New Hampshire State Cancer Registry. Exposure histories of these patients will be compared to a control group of individuals randomly selected from population lists (n=1200) . Along with a detailed personal interview, arsenic and other trace elements are being measured in toenail clipping samples using instrumental neutron activation analysis. Household water samples are being tested on selected participants using a hydride generation technique with high-resolution inductively coupled plasma mass spectrometry. In the first 793 households tested, arsenic concentrations ranged from undetectable (0.01 [mu]g/l) to 180 [mu]g/l. Over 10% of the private wells contained levels above 10 [mu]g/l and 2.5% were above 50 [mu]g/l. Based on our projected sample size, we expect at least 80% power to detect a 2-fold risk of basal cell or squamous cell skin cancer or bladder cancer among individuals with the highest 5% toenail concentrations of arsenic.Item Application of empirical interatomic potentials to the calculation of the structure and dynamics of paraffin molecules adsorbed on graphite(American Physical Society, 1979) Hansen, Flemming Y.; Taub, HaskellThe adsorption of a single molecule of ethane, propane, and butane on a basal-plane surface of graphite is investigated using empirically derived carbon-hydrogen and carbon-carbon potentials. The principal motivation for this study is the calculation of a number of structural and dynamical properties which can be compared with neutron scattering experiments on monolayer paraffin films adsorbed on graphite. For each molecule the equilibrium orientation and position with respect to the surface and contours of minimum potential energy have been calculated. We find that these molecules prefer to align themselves with their carbon skeleton parallel to the graphite basal plane with the hydrogen atoms closest to the surface occupying the center of the graphite carbon hexagons. We have also found that each of the molecules tends to distort upon adsorption by small antisymmetric rotation of the CH3 groups about the terminal C-C bonds. Two different force-constant models have been used to calculate the frequencies of the surface vibratory modes of the adsorbed molecules. The calculated frequencies and, with few exceptions, the force constants are in reasonable agreement with values inferred previously from inelastic-neutron-scattering spectra of monolayer butane films. Finally, the anharmonicity of the molecule-substrate potential has been briefly studied by examining the temperature dependence of the height of a butane molecule above the graphite basal plane and of the frequency of the molecular vibration normal to the surface.Item Structure and melting of submonolayer ethane films on graphite(American Physical Society, 1979) Coulomb, J. P.; Biberian, Jean-Paul; Suzanne, J.; Thomy, A.; Trott, Gary J. (Gary John), 1952-; Taub, Haskell; Danner, H. R.; Hansen, Flemming Y.Elastic neutron diffraction has been used to study the structure and melting of submonolayer ethane films physisorbed on exfoliated graphite. Analysis of the relative intensity of seven Bragg reflections of the film yields the molecular orientation in the close-packed solid structure observed below 63 K. At higher temperature a novel melting process occurs which we tentatively interpret as a first-order transition to an intermediate phase followed by continuous transition to the disordered state.Item Structure and growth of butane films adsorbed on graphite(American Physical Society, 1994) Herwig, K. W.; Newton, James C.; Taub, HaskellThe structure of deuterated n-butane [CD3(CD2)2CD3] adsorbed on the (0001) surfaces of an exfoliated graphite substrate has been investigated by elastic neutron diffraction. The aim of this study was to elucidate the effect of steric properties, particularly the rodlike shape of the molecule, on both the monolayer and multilayer film structure. Our principal findings are as follows: (1) The solid monolayer has a rectangular unit cell commensurate with the graphite lattice in one direction (2[square root]3 x [infinity]). Profile analysis of the monolayer diffraction pattern shows an improved fit with two molecules in the unit cell arranged in a herringbone (HB) pattern rather than the rectangular-centered structure originally proposed. The HB structure also yields a lower potential energy calculated for a monolayer cluster. (2) The growth mode of the film is ''quasiepitaxial'' at low temperature consisting of the following steps: (a) adsorption of the crystalline monolayer, (b) adsorption of a disordered second layer and compression of the monolayer, (c) onset of preferentially oriented bulk growth with continued adsorption of disordered material, (d) bilayer crystallization, and (e) reentrant growth of preferentially oriented bulk particles and disordered material. (3) A Rietveld profile analysis of the diffraction pattern obtained at a coverage of six layers is consistent with the (100) plane of the bulk butane monoclinic phase parallel to the graphite surface. (4) For coverages of two to three layers, there is evidence of a wetting transition at ~133 K, about 2 K below the bulk melting point. Both the monolayer and bulk Bragg peaks disappear and are replaced by a diffraction pattern characteristic of a liquid film with a high degree of short-range order. It is suggested that the butane molecule's steric properties are responsible for the incomplete wetting of the film as well as for the preferential orientation of the bulk phase. Our quasiepitaxial growth model for butane is similar to one proposed previously for nitrogen films on graphite. After comparing the structure and growth of the two films, we suggest that it may apply to a number of other physisorbed films composed of rod- shaped molecules having a larger aspect ratio than butane.Item Solvent effects on the monolayer structure of long n-alkane molecules adsorbed on graphite(American Physical Society, 1995) Herwig, K. W.; Matthies, Blake E. (Blake Edward), 1968-; Taub, HaskellNeutron diffraction patterns of dotriacontane ( n-C32D66) monolayers adsorbed on an exfoliated graphite substrate from a heptane ( n-C7D16) solution reveal striking differences in the molecular orientation, lattice constant, and coherence length from those of the same monolayer adsorbed from the gas phase. Neither n-C32D66 monolayer phase appears to be fully consistent with Groszek's model of n-alkane registry on the graphite (0001) surface. A reversible transformation between the two monolayer phases can be induced by adding as little as a monolayer of the heptane solvent.