• Journal of Global Scholars of Marketing Science
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• v.11
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• pp.129-146
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• 2003

This study explores whether a NBD type of model can be applied to characterize the underlying frequency distribution of online consumer's visit behavior. In this study, the following two research questions are addressed: (1) How can we characterize the underlying distribution pattern(s) of the number of repeat i i visits to a site? (2) How can consumer's Internet usages and his/her demographics affect the average number of visits to the site? Through the empirical investigation, this study found that NBD models are directly applicable to characterize the underlying distribution of visit frequency on the Internet. Furthermore, this study addresses some managerial implications for understanding how site visits are determined. Especially this study highlights the relationship between repeated visits and the visitors' Internet Usages and demographics. The proposed models are estimated and validated by online panel data that covers more than 1000 different sites and has 800,000 observations.

• Tuberculosis and Respiratory Diseases
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• v.42 no.2
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• pp.184-205
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• 1995

Background: Pulmonary toxicity by bleomycin has multiple mechanisms including direct tissue toxicity due to oxygen-derived free radicals and indirect toxicity through amplification of pulmonary inflammation. To evaluate the effect of chelators or free radical scavenger to lung damage induced by bleomycin, penicillamine as a copper chelator, deferoxamine as an iron chelator and vitamin E as a free radical scavenger were administered. Methods: Two hundred Wistar rats were divided into five groups: Control, bleomycin treated, bleomycin-penicillamine treated, bleomycin-deferoxamine treated, and bleomycin-vitamin E treated groups. Rats sacrificed on day 1, day 3, day 4, day 7, day 14, and day 28 after treatment. Bronchoalveolar lavage, light microscopic and immunohistologic studies for type I, III, IV collagens, fibronectin, laminin and NBD phallicidin were evaluated. Results: There was a significant increase in the total cell counts of bronchoalveolar lavage on day 1 from all treated animals and vitamin treated group showed an abrupt decrease in total cell counts with decrease of neutrophils on day 3. Bleomycin-vitamin E treated group had the least histologic changes such as pulmonary fibrosis. The alveolar basement membranes were positive for type IV collegen and laminin. Basement membranes of bleomycin, bleomycin-penicillamine, or bleomycin-deferoxamine treated groups were disrupted and fragmented on day 4 or 7. The bleomycin-vitamin E treated group had intact basement membranes until day 28. Conclusion: Bleomycin-induced pulmonary fibrosis was related to the severity of acute injury to oxygen radicals or activation of neutrophils and disruption of basement membrane. Vitamin E seemed to be the most effective antioxidant in the inhibition of bleomycin-induced pulmonary injury and fibrosis.

• Journal of the Korean Society of Food Science and Nutrition
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• v.26 no.4
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• pp.743-750
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• 1997

Direct measurement of the kinetics of free fatty acid transfer between phospholipid model membrane is technically limited by the rapid nature of the transfer process. Separation of membrane-bound fatty acid by centrifugation has shown that although the equilibrium distribution of free fatty acid is determined by this method, fatty acid transfer occurs too rapidly for accurate kinetic measurements. Recently fluorescence resonance energy transfer(FRET) assay has been developed to examine transfer of fatty acids between membranes. Donor membranes which has fluorescent fatty acid, anthroyloxy fatty acid(AOFA), is mixed with acceptor membranes which has non-interchangeable fluorescent quencher, nitrobenzo-xadiazol(NBD), using stopped flow apparatus. As the fluorescent fatty acids transfer from donor membrane to acceptor membrane, fluorescence intensity would be decreased and the rate and degree of fatty acid transfer can be analyzed. Fatty acid transfer between micelles is more complicated because of bile salt. Therefore in experiments with micelles, fluorescence self quenching assay is used. At high concentrations, a fluorophore tends to quench its own fluorescence causing a reduction in fluorescence intensity. Donor micelles contained self quenching concentrations of fluorophore and acceptor micelles had no fluorophore. Upon mixing of donor and acceptor micelles, the rate of transfer of the fluorophore from the donor to the acceptor was measured by monitoring the release in self quenching when its concentration in donor decreased over time.