Simultaneous Linking of Cross-Informant and Longitudinal Data Involving Positive Family Relationships.

Measurement invariance is a prerequisite when comparing different groups of individuals or when studying a group of individuals across time. This assures that the same construct is assessed without measurement artifacts. This investigation applied a novel approach of simultaneous parameter linking to cross-sectional and longitudinal measures of the construct of positive family relationships. Previously, a scale to measure this construct in mothers was developed longitudinally using the nominal response model of item response theory. In this study, this methodology was conducted for the first time to develop such a scale for children. The data for both informants derived from the Fullerton Longitudinal Study and encompassed 9 annual assessments spanning 8-years (age 9-17 years). This permitted linking across informants studied concurrently and prospectively. This procedure minimized measurement error, furnished a common metric across informants and time and established measurement invariance. Resulting thetas revealed a significant degree of concordance between informants across assessment waves as well as stability of individual differences for both informants over time. This psychometric investigation is unique because it simultaneously established invariance of a construct across informants and time. Implications for future research are discussed.

A Novel High-Throughput Viscometer.

A novel, rapid, parallel, and high-throughput system for measuring viscosity of materials under different conditions of shear rate, temperature, time, etc., has been developed. This unique system utilizes the transient flow of a complex fluid through pipettes. This approach offers significant practical advantages over microfluidic-based devices for viscosity screening: no cleanup is required, the method is high throughput (<1 h for 100 samples), and only small sample volumes (<1 mL) are used. This paper details for the first time the experimental and modeling efforts to implement this mass- and pressure-based viscosity measurement concept as a robust viscosity estimation tool. This approach is very well-suited for viscosity measurements in high-throughput formulation workflows, as it is rapid and parallel and operates directly on samples in various microtiter plate formats. We present systematic experimental observations together with numerical and analytical modeling approaches to characterize instrument capabilities and limitations. The complex transient flow of fluids through these pipettes leads to data-rich pressure profiles. Numerical and analytical modeling is then used to extract viscosity and other rheological parameters from these pressure profiles. We have successfully utilized this viscosity screening tool for a multitude of complex fluids including oils, paints, solvents, and detergents.