2 research outputs found
Sensitivity analysis and choosing between alternative polytomous IRT models using Bayesian model comparison criteria
<p>Polytomous Item Response Theory (IRT) models are used by specialists to score assessments and questionnaires that have items with multiple response categories. In this article, we study the performance of five model comparison criteria for comparing fit of the graded response and generalized partial credit models using the same dataset when the choice between the two is unclear. Simulation study is conducted to analyze the sensitivity of priors and compare the performance of the criteria using the No-U-Turn Sampler algorithm, under a Bayesian approach. The results were used to select a model for an application in mental health data.</p
Remarkable Viscoelasticity in Mixtures of Cyclodextrins and Nonionic Surfactants
We report the effect of native cyclodextrins
(α, β,
and γ) and selected derivatives in modulating the self-assembly
of the nonionic surfactant polyoxyethylene cholesteryl ether (ChEO<sub>10</sub>) and its mixtures with triethylene glycol monododecyl ether
(C<sub>12</sub>EO<sub>3</sub>), which form wormlike micelles. Cyclodextrins
(CDs) generally induce micellar breakup through a host–guest
interaction with surfactants; instead, we show that a constructive
effect, leading to gel formation, is obtained with specific CDs and
that the widely invoked host–guest interaction may not be the
only key to the association. When added to wormlike micelles of ChEO<sub>10</sub> and C<sub>12</sub>EO<sub>3</sub>, native β-CD, 2-hydroxyethyl-β-CD
(HEBCD), and a sulfated sodium salt of β-CD (SULFBCD) induce
a substantial increase of the viscoelasticity, while methylated CDs
rupture the micelles, leading to a loss of the viscosity, and the
other CDs studied (native α- and γ- and hydroxypropylated
CDs) show a weak interaction. Most remarkably, the addition of HEBCD
or SULFBCD to pure ChEO<sub>10</sub> solutions (which are low-viscosity,
Newtonian fluids of small, ellipsoidal micelles) induces the formation
of transparent gels. The combination of small-angle neutron scattering,
dynamic light scattering, and cryo-TEM reveals that both CDs drive
the elongation of ChEO<sub>10</sub> aggregates into an entangled network
of wormlike micelles. <sup>1</sup>H NMR and fluorescence spectroscopy
demonstrate the formation of inclusion complexes between ChEO<sub>10</sub> and methylated CDs, consistent with the demicellization
observed. Instead, HEBCD forms a weak complex with ChEO<sub>10</sub>, while no complex is detected with SULFBCD. This shows that inclusion
complex formation is not the determinant event leading to micellar
growth. HEBCD:ChEO<sub>10</sub> complex, which coexists with the aggregated
surfactant, could act as a cosurfactant with a different headgroup
area. For SULFBCD, intermolecular interactions via the external surface
of the CD may be more relevant