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

A Voltage Control Strategy of VSG Based on Self-Adaptive Inertia Coefficient and Droop Coefficient

With the increasing penetration rate of distributed renewable energy in power systems, the control strategy of virtual synchronous generator (VSG) is widely used for several years. Some existing VSG control strategies have been able to solve the stability problems caused by the abnormal grid voltage, but the effects of the inertia coefficient and the droop coefficient on the voltage stability are not taken into account. In order to further improve the voltage stability of the microgrid system, a voltage control strategy of VSG based on self-adaptive inertia coefficient and droop coefficient is proposed in this paper. When the voltage is far from the steady state, the increase of the inertia coefficient can decrease the voltage deviation. On the contrary, when it is close to the steady state, the decrease of the inertia coefficient can make the system response speed accelerate. According to the real-time voltage deviation, the droop coefficient can change adaptively to decrease the adjusting time and the voltage deviation during the disturbance. Finally, the simulation model of VSG is built by MATLAB/Simulink for conducting simulation experiments. Compared with other strategies, the correctness and effectiveness of the proposed control strategy are validated

pH-Regulated Ionic Conductance in a Nanochannel with Overlapped Electric Double Layers

Accurately and rapidly analyzing the ionic current/conductance in a nanochannel, especially under the condition of overlapped electric double layers (EDLs), is of fundamental significance for the design and development of novel nanofluidic devices. To achieve this, an analytical model for the surface charge properties and ionic current/conductance in a pH-regulated nanochannel is developed for the first time. The developed model takes into account the effects of the EDL overlap, electroosmotic flow, Stern layer, multiple ionic species, and the site dissociation/association reactions on the channel walls. In addition to good agreement with the existing experimental data of nanochannel conductance available from the literature, our analytical model is also validated by the full model with the Poisson–Nernst–Planck and Navier–Stokes equations. The EDL overlap effect is significant at small nanochannel height, low salt concentration, and medium low pH. Neglecting the EDL overlap effect could result in a wrong estimation in the zeta potential and conductance of the nanochannel in a single measurement