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

Research and optimization of acoustic environment in ordinary classrooms of middle school

A good classroom acoustic environment will contribute to teachers’ health and students’ learning. Comfortable acoustic environment requires suitable reverberation time, sufficient loudness, uniform sound field distribution, high language clarity, and no acoustic defects such as echo and acoustic focusing. In this study, the optimization strategy of acoustic environment is proposed through the investigation, field testing and numerical simulation analysis of a middle school classroom in Wenzhou under different ventilation conditions. The results show: the key factors affecting the classroom acoustic environment are outdoor activity noise, corridor noise, and classroom teacher-student activity noise. Through optimization, the quality of classroom acoustic environment is improved significantly. Classroom reverberation time (intermediate frequency) decreased from 1.5s to 0.7s; ALC decreased from 9.65% to 4.75%; STI increased from 0.534 to 0.664. The research results provided reference for acoustic design of secondary school classrooms in the future

High-Safety Nonaqueous Electrolytes and Interphases for Sodium-Ion Batteries

Rapidly developed Na-ion batteries are highly attractive for grid energy storage. Nevertheless, the safety issues of Na-ion batteries are still a bottleneck for large-scale applications. Similar to Li-ion batteries (LIBs), the safety of Na-ion batteries is considered to be tightly associated with the electrolyte and electrode/electrolyte interphase. Although the knowledge obtained from LIBs is helpful, designing safe electrolytes and obtaining stable interphases in Na-ion batteries is still a huge challenge. Therefore, it is of significance to investigate the key factors and develop new strategies for the development of high-safety Na-ion batteries. This comprehensive review introduces the recent efforts from nonaqueous electrolytes and interphase aspects of Na-ion batteries, proposes their design strategies and requirements for improving safety characteristics, and discusses the potential issues for practical applications. The insight to formulate safe electrolytes and design the stable interphase for Na-ion batteries with high safety is intended to be provided herein

Chromium-Modified Li₄Ti₅O₁₂ with a Synergistic Effect of Bulk Doping, Surface Coating, and Size Reducing

Bulk doping, surface coating, and size reducing are three strategies for improving the electrochemical properties of Li₄Ti₅O₁₂ (LTO). In this work, chromium (Cr)-modified LTO with a synergistic effect of bulk doping, surface coating, and size reducing is synthesized by a facile sol–gel method. X-ray diffraction (XRD) and Raman analysis prove that Cr dopes into the LTO bulk lattice, which effectively inhibits the generation of TiO₂ impurities. Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) verifies the surface coating of Li₂CrO₄ on the LTO surface, which decreases impedance of the LTO electrode. More importantly, the size of LTO particles can be significantly reduced from submicroscale to nanoscale as a result of the protection of the Li₂CrO₄ surface layer and the suppression from Cr atoms on the long-range order in the LTO lattice. As anode material, Li_4‑<i>x</i>Cr_3<i>x</i>Ti_{5–2<i>x</i>}O₁₂ (<i>x</i> = 0.1) delivers a reversible capacity of 141 mAh g^–1 at 10 °C, and over 155 mAh g^–1 at 1 °C after 1000 cycles. Therefore, the Cr-modified Li₄Ti₅O₁₂ prepared via a sol–gel method has potential for applications in high-power, long-life lithium-ion batteries

Preparation of N-doped porous carbon matrix in a solid–liquid coexisted NaCl template and its applications in Li–S batteries

Li–S batteries have beenconsidered as the most desirable candidate for next-generation batteries because of their high energy density and low cost, although the problems of the insulating nature of S and Li2S and the “shuttle effect” of polysulfides in Li–S batteries have to be addressed. In this work, we propose NaCl templates and a solid–liquid coexistence strategy to synthesize an N-doped carbon matrix with interconnected micro-mesoporous structure. Benefiting from the critical state of solid–liquid coexistence at the melting point of NaCl and a pretreatment by pressure, a unique porous structure with an interconnected network of micropores and mesopores is obtained. The micropores can prevent the dissolution of polysulfides, the mesopores can increase the S loading, and the interconnected pore network can significantly improve the usage of active materials. As a result, the cathode with the N-doped carbon matrix shows improved electrochemical performances

Lithium Difluorophosphate as a Dendrite-Suppressing Additive for Lithium Metal Batteries

The notorious lithium (Li) dendrites and the low Coulombic efficiency (CE) of Li anode are two major obstacles to the practical utilization of Li metal batteries (LMBs). Introducing a dendrite-suppressing additive into nonaqueous electrolytes is one of the facile and effective solutions to promote the commercialization of LMBs. Herein, Li difluorophosphate (LiPO₂F_2, LiDFP) is used as an electrolyte additive to inhibit Li dendrite growth by forming a vigorous and stable solid electrolyte interphase film on metallic Li anode. Moreover, the Li CE can be largely improved from 84.6% of the conventional LiPF₆-based electrolyte to 95.2% by the addition of an optimal concentration of LiDFP at 0.15 M. The optimal LiDFP-containing electrolyte can allow the Li||Li symmetric cells to cycle stably for more than 500 and 200 h at 0.5 and 1.0 mA cm^–2, respectively, much longer than the control electrolyte without LiDFP additive. Meanwhile, this LiDFP-containing electrolyte also plays an important role in enhancing the cycling stability of the Li||LiNi_1/3Co_1/3Mn_1/3O₂ cells with a moderately high mass loading of 9.7 mg cm^–2. These results demonstrate that LiDFP has extensive application prospects as a dendrite-suppressing additive in advanced LMBs