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- Pink, David A., et al.
(författare)
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Modeling the solid-liquid phase transition in saturated triglycerides
- 2010
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 132:5, s. 054502/1-054502/11
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Tidskriftsartikel (refereegranskat)abstract
- We investigated theor. two competing published scenarios for the melting transition of the triglyceride trilaurin (TL): those of (1) Corkery et al., in which the av. state of each TL mol. in the liq. phase is a discotic "Y" conformer whose three chains are dynamically twisted, with an av. angle of ∌120° between them, and those of (2) Cebula et al., in which the liq.-state conformation of the TL mol. in the liq. phase is a nematic h*-conformer whose three chains are in a modified "chair" conformation. We developed two competing models for the two scenarios, in which TL mols. are in a nematic compact-chair (or "h") conformation, with extended, possibly all-trans, chains at low-temps., and in either a Y conformation or an h* conformation in the liq. state at temps. higher than the phase-transition temp., T* = 319 K. We defined an h-Y model as a realization of the proposal of R. Corkery et al. (2007), and explored its predictions by mapping it onto an Ising model in a temp.-dependent field, performing a mean-field approxn., and calcg. the transition enthalpy ΔH. We found that the most plausible realization of the h-Y model, as applied to the solid-liq. phase transition in TL, and likely to all satd. triglycerides, gave a value of ΔH in reasonable agreement with the expt. We then defined an alternative h-h* model as a realization of the proposal of D. J. Cebula et al. (1992), in which the liq. phase exhibits an av. symmetry breaking similar to an h conformation, but with twisted chains, to see whether it could describe the TL phase transition. The h-h* model gave a value of ΔH that was too small by a factor of ∌3-4. We also predicted the temp. dependence of the 1132 cm-1 Raman band for both models, and performed measurements of the ratios of three TL Raman bands in the temp. range of -20° ≀ T ≀ 90°. The exptl. results were in accord with the predictions of the h-Y model and support the proposal of that the liq. state is made up of mols. that are each, on av., in a Y conformation. Finally, we carried out computer simulations of minimal-model TLs in the liq. phase, and concluded that although the individual TL mols. are, on av., Y conformers, long-range discotic order is unlikely to exist.
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| 3. |
- Pink, David A, et al.
(författare)
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Modeling the solid-liquid phase transition in saturated triglycerides
- 2010
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Ingår i: Journal of Chemical Physics. - 0021-9606 .- 1089-7690. ; 132:5
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Tidskriftsartikel (refereegranskat)abstract
- We investigated theoretically two competing published scenarios for the melting transition of the triglyceride trilaurin (TL): those of (1) Corkery et al. [Langmuir 23, 7241 (2007)], in which the average state of each TL molecule in the liquid phase is a discotic "Y" conformer whose three chains are dynamically twisted, with an average angle of similar to 120 degrees between them, and those of (2) Cebula et al. [J. Am. Oil Chem. Soc. 69, 130 (1992)], in which the liquid-state conformation of the TL molecule in the liquid phase is a nematic h*-conformer whose three chains are in a modified "chair" conformation. We developed two competing models for the two scenarios, in which TL molecules are in a nematic compact-chair (or "h") conformation, with extended, possibly all-trans, chains at low-temperatures, and in either a Y conformation or an h* conformation in the liquid state at temperatures higher than the phase-transition temperature, T*=319 K. We defined an h-Y model as a realization of the proposal of Corkery et al. [Langmuir 23, 7241 (2007)], and explored its predictions by mapping it onto an Ising model in a temperature-dependent field, performing a mean-field approximation, and calculating the transition enthalpy Delta H. We found that the most plausible realization of the h-Y model, as applied to the solid-liquid phase transition in TL, and likely to all saturated triglycerides, gave a value of Delta H in reasonable agreement with the experiment. We then defined an alternative h-h* model as a realization of the proposal of Cebula et al. [J. Am. Oil Chem. Soc. 69, 130 (1992)], in which the liquid phase exhibits an average symmetry breaking similar to an h conformation, but with twisted chains, to see whether it could describe the TL phase transition. The h-h* model gave a value of Delta H that was too small by a factor of similar to 3-4. We also predicted the temperature dependence of the 1132 cm(-1) Raman band for both models, and performed measurements of the ratios of three TL Raman bands in the temperature range of -20 degrees C <= T <= 90 degrees C. The experimental results were in accord with the predictions of the h-Y model and support the proposal of Corkery et al. [Langmuir 23, 7241 (2007)] that the liquid state is made up of molecules that are each, on average, in a Y conformation. Finally, we carried out computer simulations of minimal-model TLs in the liquid phase, and concluded that although the individual TL molecules are, on average, Y conformers, long-range discotic order is unlikely to exist.
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- Rahman, Jakaria, 1977, et al.
(författare)
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Assessment of expertise overlap between an expert panel and research groups
- 2014
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Ingår i: Proceedings of the science and technology indicators conference. ; , s. 295-301
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Konferensbidrag (refereegranskat)abstract
- Discipline-specific research evaluation exercises are typically carried out by committees of peers, expert panels. Currently, there are no available methods that can measure overlap in expertise between a panel and the units of assessment. This research in progress paper explores a bibliometric approach to determining the overlap of expertise, using the 2010 research evaluation of nine physics research groups of the University of Antwerp as a test case. Overlay maps were applied to visualize to what extent the groups and panel members publish in different Web of Science subject categories. There seems to be a moderate disparity between the panel’s and the groups’ expertise. The panel was not as diverse as the groups that needed to be assessed. Future research will focus on journal level overlay maps, similarity testing, and a comparison with other disciplines.
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