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A molecular beam scattering investigation of the oxidation of CO on Rh(111). II. Angular and velocity distributions of the CO2 product (1989)

Brown, L. S. ; Sibener, S. J.

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 90 (1989), S. 2807-2815

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ISSN: 1089-7690

Source: AIP Digital Archive

Topics: Physics , Chemistry and Pharmacology

Notes: Molecular beam and time of flight methods have been used to examine the angular distributions and velocity distributions of the CO2 product molecules formed in the catalytic oxidation of CO on a Rh(111) single crystal in the surface temperature range 700–1000 K. The angular distribution was sharply peaked about the surface normal, and cannot be described by a simple cosn θ expression. No temperature dependence was observed in the angular distribution over the range of temperatures studied here. Observed velocity distributions were clearly non-Maxwellian and had average translational energies in excess of those expected at the surface temperatures. Furthermore, the average velocity depended strongly on the desorption angle. Molecules desorbing along the surface normal had an average translational energy of ∼8 kcal/mol. The average energy decreased with increasing angle, reaching a value of ∼4 kcal/mol at an angle of 60°. All of the observed velocity distributions were narrower than Maxwellian distributions with the same average energies. Product velocity distributions did not appear to vary with surface temperature. The observed excess energies are believed to arise from the crossing of the activation barrier to reaction, with a fraction of the reaction energy being carried away from the surface by the product molecules.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.455930

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The influence of age, race, and gender on peripheral blood mononuclear-cell subsets in healthy nonsmokers (1989)

Tollerud, D. J. ; Clark, J. W. ; Brown, L. Morris ; [et al.]

Springer

Journal of clinical immunology 9 (1989), S. 214-222

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ISSN: 1573-2592

Keywords: Lymphocyte subsets ; normal values ; flow cytometry ; age ; race ; gender

Source: Springer Online Journal Archives 1860-2000

Topics: Medicine

Notes: Abstract To investigate the influence of age, race, and gender on the cellular immune system, we determined T-cell, B-cell, monocyte, natural killer (NK)-cell, and HLA-DR+-cell subsets in 266 nonsmokers from a population-based random sample of healthy adults using monoclonal antibodies and flow cytometry. Blacks had a lower total white blood-cell count than whites (P≤0.0001), due primarily to a decrease in granulocytes. There was no significant difference in absolute lymphocyte count between blacks and whites. Blacks had a higher proportion of CD19+ cells (Leu 12+ B cells) and a lower proportion of CD3+ cells (OKT3+ T cells) than whites (P≤0.01). Female sex and increasing age were independently associated with an increased percentage of CD4+ cells (OKT4A+ helper-inducer T-cell subset), resulting in a higher helper/suppressor ratio among women and older individuals (P≤0.05). Black race and increasing age were independently associated with an increased proportion of HLA-DR+ cells (P≤0.0001) which was not attributable to B cells or monocytes. No significant age, race, or gender effects were observed for CD14+ cells (Leu M3+ monocytes) or CD16+ cells (Leu 11A+ natural killer cells). These data demonstrate that age, race, and gender are each associated with significant differences in peripheral blood monouclear-cell subsets. Population-based data such as these provide an important foundation for future design and interpretation of human flow cytometry data.