2 resultados para PH

em Bucknell University Digital Commons - Pensilvania - USA


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We propose a new model, the Author Affiliation Index (AAI), for examining journal quality, explain how the AAI is calculated, and report the resulting scores for 35 accounting and accounting-related journals. Next, we compare AAI journal rankings with those from other published studies and examine the correlations between them to show how the AAI can be used to evaluate relatively new journals, such as Accounting and the Public Interest, that are not included in extant ranking lists. By explaining its flexibility, we demonstrate that the AAI model can serve as a valuable tool for measuring journal quality and for meeting AACSB accreditation requirements for faculty groups as well as individual faculty. The AAI is based on the principle that as the percentage of authors in a journal who are accounting faculty at doctoral-granting institutions increases, the perceived value of that journal in terms of quality to Ph.D.-granting accounting programs also increases. Although our illustrations focus on the construction of this measure for use by Ph.D.-granting institutions, we describe how it can be adapted for use by other faculty groups.

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Micelle-forming bile salts have previously been shown to be effective pseudo-stationary phases for separating the chiral isomers of binaphthyl compounds with micellar electrokinetic capillary chromatography (MEKC). Here, cholate micelles are systematically investigated via electrophoretic separations and NMR using R, S-1, 1¿- binaphthyl- 2, 2¿-diylhydrogenphosphate (BNDHP) as a model chiral analyte. The pH, temperature, and concentration of BNDHP were systematically varied while monitoring the chiral resolution obtained with MEKC and the chemical shift of various protons in NMR. NMR data for each proton on BNDHP is monitored as a function of cholate concentration: as cholate monomers begin to aggregate and the analyte molecules begin to sample the micelle aggregate we observe changes in the cholate methyl and S-BNDHP proton chemical shifts. From such NMR data, the apparent CMC of cholate at pH 12 is found to be about 13-14 mM, but this value decreases at higher pH, suggesting that more extreme pHs may give rise to more effective separations. In general, CMCs increase with temperature indicating that one may be able to obtain better separations at lower temperatures. S-BNDHP concentrations ranging from 50 ¿M to 400 ¿M (pH 12.8) gave rise to apparent cholate CMC values from 10 mM to 8 mM, respectively, indicating that S-BNDHP, the chiral analyte molecule, may play an active role in stabilizing cholate aggregates. In all, these data show that NMR can be used to systematically investigate a complex multi-variable landscape of potential optimizations of chiral separations.