Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data

Effect of Fluorinated Substituents on Solubility and Dielectric Properties of the Liquid Crystalline Poly(ester imides)

With the rapid advancement of 5G communication technology, much attention has been paid on high-performance polymers with a low dielectric constant (Dk), a low dielectric loss (Df) and good processability. In order to further research and improve dielectric properties of the liquid crystalline poly(ester imide)s (LCPEIs), four imide dicarboxylic acids (IAs) with fluorinated groups are designed and synthesized. They are then copolymerized with 1,3-phthalic acid (IPA), p-hydroxybenzoic acid (HBA), and bisphenol monomers via solution polycondensation to obtain fluorinated PEIs, whose fluorine content, position of the fluorinated group, and LC behavior are tunable by using different IAs and bisphenol monomers. These PEIs with the highest Tg of 238 °C are soluble in general organic solvents, such as m-cresol, N-methyl-2-pyrrolidone (NMP), chloroform, and so on. PEI-6F25AF exhibits the lowest Dk of 2.60, while LCPEI-6FD shows the lowest Df of 0.0053 at 10 GHz. It is found that high fluorine content and large pendent group can reduce the Dk, while the fluorinated group grafted close to the nitrogen atom and the LC rigid rod-like conformation lead to low Df. We devoutly expect that this research offers some reference for structure design of LCPEIs with both low Dk and Df at high frequency

Associations between individual and environmental factors and habitual physical activity among older Chinese adults: A social–ecological perspective

Purpose: To examine, within a social–ecological framework, associations between multifaceted individual and environmental factors and habitual physical activity (HPA) among older Chinese adults. Methods: Through a mix of qualitative and quantitative methods, a survey instrument assessing various factors underlying 3 social–ecological dimensions of intrapersonal, interpersonal, and community and environmental resources was developed. Using a cross-sectional design, older adults (n = 1580, aged 67 ± 7 years) recruited from 10 communities in Shandong province completed the social–ecological survey of HPA. Data were analyzed using Partial Least Squares Path Modeling. Results: Factors related to intrapersonal (medical knowledge, motivation, physical function, sport skills, socioeconomic status, and education), interpersonal (social support, social activity, and social norms), and community and physical environmental resources (safety, capacity, availability of and access to physical activity facilities) were found to be significantly associated with older adults' participation in HPA. Conclusion: The findings provide an initial validation of a social–ecological approach to the study of HPA in China, suggesting that strategies aimed at promoting physical activity in older adults should address multiple levels of factors that may contribute to the likelihood of older Chinese adults being physically active

Uniformly-Dispersed Black Phosphorene as Flame-Retardant Epoxy Composites via Iterative Dispersion Strategy

Black phosphorus (BP) nanosheets are widely used in flame retardant polymers, but the challenge of poor dispersion in polymers increases their additions and raises the cost of BP-based flame-retardant materials. Here, we propose an iterative dispersion strategy that gradually approaches a homogeneous dispersion state by separating aggregates and dispersions in the BP partial dispersion with multiple cycles. An iron(III) trifluoromethanesulfonate functionalized BP (BFF) is utilized for the flame retardant and reinforcing modification of the epoxy matrix to verify the reliability of this strategy, noting that the F element in BFF can achieve dynamic hydrogen bonds with the epoxy-amine system during the curing process, further promoting dispersion. Therefore, epoxy thermosets with only 0.2 wt % BFF loading achieve UL-94 V-0 level with a limiting oxygen index (LOI) of 29.2% through the synergistic effect of iterative dispersion and dynamic hydrogen bond. The formation of hydrogen bonds between BFF and the epoxy matrix also contributes to a significant increase in the mechanical properties. This work provides a reasonable and facile concept to achieve sufficient dispersion of inorganic nanosheets in polymer or organic matrices and also promotes the process of industrial large-scale manufacturing of BP-based fire-retardant materials

Uniformly-Dispersed Black Phosphorene as Flame-Retardant Epoxy Composites via Iterative Dispersion Strategy

Black phosphorus (BP) nanosheets are widely used in flame retardant polymers, but the challenge of poor dispersion in polymers increases their additions and raises the cost of BP-based flame-retardant materials. Here, we propose an iterative dispersion strategy that gradually approaches a homogeneous dispersion state by separating aggregates and dispersions in the BP partial dispersion with multiple cycles. An iron(III) trifluoromethanesulfonate functionalized BP (BFF) is utilized for the flame retardant and reinforcing modification of the epoxy matrix to verify the reliability of this strategy, noting that the F element in BFF can achieve dynamic hydrogen bonds with the epoxy-amine system during the curing process, further promoting dispersion. Therefore, epoxy thermosets with only 0.2 wt % BFF loading achieve UL-94 V-0 level with a limiting oxygen index (LOI) of 29.2% through the synergistic effect of iterative dispersion and dynamic hydrogen bond. The formation of hydrogen bonds between BFF and the epoxy matrix also contributes to a significant increase in the mechanical properties. This work provides a reasonable and facile concept to achieve sufficient dispersion of inorganic nanosheets in polymer or organic matrices and also promotes the process of industrial large-scale manufacturing of BP-based fire-retardant materials