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Differential cross sections for ionization of water vapor by high-velocity bare ions and electrons (1987)

Miller, J. H. ; Wilson, W. E. ; Manson, S. T. ; [et al.]

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

The Journal of Chemical Physics 86 (1987), S. 157-162

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ISSN: 1089-7690

Source: AIP Digital Archive

Topics: Physics , Chemistry and Pharmacology

Notes: A semiempirical model of single differential cross sections (SDCS) for ionization of water vapor by fast electrons and bare ions is presented. At low secondary-electron energy, the model is based on an asymptotic expansion of the first Born approximation with coefficients, that are independent of projectile properties, evaluated from experimental photoabsorption and proton-impact ionization data. As the secondary-electron energy increases, the model converges to a binary-encounter approximation. Comparisons with measured differential, total, and dissociative cross sections for ionization of water by fast electrons are used to test the model. For primary electrons with energy greater than about 500 eV, agreement with these data is generally within experimental uncertainty; however, some discrepancies of uncertain origin exist.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.452774

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The role of asymmetric cell division in pteridophyte cell differentiation. I. Localized metal accumulation and differentiation inVittaria gemmae andOnoclea prothallia (1987)

Kotenko, J. L. ; Miller, J. H. ; Robinson, A. I.

Springer

Protoplasma 136 (1987), S. 81-95

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ISSN: 1615-6102

Keywords: Asymmetric cytokinesis ; Cell differentiation ; Localized Ca2+ accumulation ; Nuclear migration ; Onoclea ; Vittaria

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Summary In gemmae ofVittaria graminifolia and prothallia ofOnoclea sensibilis, cell differentiation is initiated by nuclear migration and geometrically asymmetric cell division. The small daughter cells inVittaria develop into antheridia in the presence of gibberellic acid or into rhizoids or new prothallia in its absence. Antheridial differentiation from asymmetric division is induced inOnoclea byPteridium antheridiogen, whereas rhizoid or vegetative cell formation occurs in its absence. Although asymmetric cytokinesis initiates differentiation, it does not in itself determine the developmental fate of the smaller cell. Several histochemical techniques demonstrate that prior to nuclear migration and cell division, Ca2+ accumulates in the cytoplasm and wall of the cell at the site where asymmetric division will occur, regardless of the developmental fate of the small cell. The cytoplasmic localization of Ca2+ appears to reflect a mobilization of Ca2+ from within the cell that eventually moves into the cell wall. We propose that this internal accumulation of Ca2+ leads to a localized decrease in cytosolic [Ca2+] which in turn may regulate developmental events such as nuclear migration.