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

On the use of geometrically exact shells for dynamic tire simulation

In the present work a tire is modeled by using geometrically exact shells. The discretization is done with the help of isoparametric quadrilateral finite elements. The interpolation is performed with linear Lagrangian polynomials for the midsurface as well as for the director field. As time stepping method for the resulting differential algebraic equation a modified backward differential formula rule is chosen. To handle the interaction with a rigid road surface, a one sided normal contact formulation is introduced. An orthotropic material model for geometrically exact shells derived from 3D continuum theory is introduced, to describe the anisotropic behavior of the tire material. Inflation pressure is taken into account with a configuration dependent force. The interaction between the multibody system of a car and the tire is realized via co-simulation. Some quasi-static simulations are presented and compared to measurements on a real tire

An ABAQUS Implementation of a Solid-Shell Element: Application to Low Velocity Impact

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