Georgetown University

About: Georgetown University is a education organization based out in Washington D.C., District of Columbia, United States. It is known for research contribution in the topics: Population & Cancer. The organization has 23377 authors who have published 43718 publications receiving 1748598 citations. The organization is also known as: GU & Georgetown.

The Effects of Job Embeddedness on Organizational Citizenship, Job Performance, Volitional Absences, and Voluntary Turnover

Abstract: This study extends theory and research on job embeddedness, which was disaggregated into its two major subdimensions, on-the-job and off-the-job embeddedness. As hypothesized, regression analyses r...

Molecular organogels. Soft matter comprised of low-molecular-mass organic gelators and organic liquids.

Abstract: This Account presents recent advances in understanding how and why dilute solutions/sols of low-molecular-mass organic gelators (LMOGs) undergo microscopic phase separation to form self-assembled fibrillar networks in molecular organogels. Concepts are illustrated structurally at the subnanometer (molecular) to several millimeter (bulk) length scales and dynamically over time scales that follow the assembly of supersaturated solutions/sols into gel phases. Examples include both structurally complicated (ALS molecules with aromatic, linking, and steroidal groups) and simple (n-alkanes or n-alkanes along whose chains a hetero-group has been inserted) LMOGs in a wide range of organic liquids.

Active Tamoxifen Metabolite Plasma Concentrations After Coadministration of Tamoxifen and the Selective Serotonin Reuptake Inhibitor Paroxetine

Abstract: Background: Tamoxifen, a selective estrogen receptor modulator (SERM), is converted to 4-hydroxy-tamoxifen and other active metabolites by cytochrome P450 (CYP) enzymes. Selective serotonin reuptake inhibitors (SSRIs), which are often prescribed to alleviate tamoxifen-associated hot flashes, can inhibit CYPs. In a prospective clinical trial, we tested the effects of coadministration of tamoxifen and the SSRI paroxetine, an inhibitor of CYP2D6, on tamoxifen metabolism. Methods: Tamoxifen and its metabolites were measured in the plasma of 12 women of known CYP2D6 genotype with breast cancer who were taking adjuvant tamoxifen before and after 4 weeks of coadministered paroxetine. We assessed the inhibitory activity of pure tamoxifen metabolites in an estradiol-stimulated MCF7 cell proliferation assay. To determine which CYP isoforms were involved in the metabolism of tamoxifen to specific metabolites, we used CYP isoform‐specific inhibitors. All statistical tests were two-sided. Results: We separated, purified, and identified the metabolite 4-hydroxy-N-desmethyl-tamoxifen, which we named endoxifen. Plasma concentrations of endoxifen statistically significantly decreased from a mean of 12.4 ng/mL before paroxetine coadministration to 5.5 ng/mL afterward (difference 6.9 ng/mL, 95% confidence interval [CI] 2.7 to 11.2 ng/mL) (P .004). Endoxifen concentrations decreased by 64% (95% CI 39% to 89%) in women with a wild-type CYP2D6 genotype but by only 24% (95% CI 23% to 71%) in women with a variant CYP2D6 genotype (P .03). Endoxifen and 4-hydroxy-tamoxifen inhibited estradiol-stimulated MCF7 cell proliferation with equal potency. In vitro, troleandomycin, an inhibitor of CYP3A4, inhibited the demethylation of tamoxifen to N-desmethyl-tamoxifen by 78% (95% CI 65% to 91%), and quinidine, an inhibitor of CYP2D6, reduced the subsequent hydroxylation of N-desmethyl-tamoxifen to endoxifen by 79% (95% CI 50% to 108%). Conclusions: Endoxifen is an active tamoxifen metabolite that is generated via CYP3A4-mediated N-demethylation and CYP2D6-mediated hydroxylation. Coadministration of paroxetine decreased the plasma concentration of endoxifen. Our data suggest that CYP2D6 genotype and drug interactions should be considered in women treated with tamoxifen. [J Natl Cancer Inst 2003;95:1758 ‐ 64]

Conversational Interaction and Second Language Development: Recasts, Responses, and Red Herrings?

Abstract: This article examines the effects of negotiated interaction on the production and development of question forms in English as a second language (ESL). The study focused on one feature of interaction, recasts, which have recently been the topic of interactional work in the SLA literature (Long, 1996; Long, Inagaki, & Ortega, this issue; Lyster & Ranta, 1997; Oliver, 1995). The study compared groups of learners who received interactionally modified input with learners who received the same input containing intensive recasts in order to investigate: (a) the effect of recasts on learners' short term interlanguage (IL) development, and (b) the nature and content of learners' responses to recasts. The results suggest that for more advanced learners, interaction with intensive recasts may be more beneficial than interaction alone in facilitating an increase in production of targeted higher-level morphosyntactic forms. These positive developmental effects were found for recasts even though, as is generally acknowledged in the discourse, recasts were usually not repeated and rarely elicited modification by the learners. This study, therefore, suggests that recasts may be beneficial for short term IL development even though they are not incorporated in learners' immediate responses. In fact, the responses may be red herrings.

Electronic survey methodology: A case study in reaching hard-to-involve internet users.

Abstract: Using the Internet to conduct quantitative research presents challenges not found in conventional research. Paper-based survey quality criteria cannot be completely adapted to electronic formats. Electronic surveys have distinctive technological, demographic, and response characteristics that affect their design, use, and implementation. Survey design, participant privacy and confidentiality, sampling and subject solicitation, distribution methods and response rates, and survey piloting are critical methodological components that must be addressed. In this article, quality criteria for electronic survey design and use based on an investigation of recent electronic survey literature are presented. The application of these criteria to reach a hard-to-involve online population-nonpublic participants of online communities (also known as "lurkers")-and survey them on their community participation, a topic not salient to the purpose of their online communities is demonstrated in a case study. The results show t...