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

Cooperative localization of a cascading quadrilateral network

In this paper, we introduce a set of sensor networks, called the cascading quadrilateral network, and study how to compute the positions of its nodes in a cooperative way. We investigate the condition for determining whether all the sensor nodes are localizable. If not, we provide a method to detect the un-localizable nodes for the whole network. The necessary and sufficient conditions for the network localizability and node localizability are given from the view of algebraic property, respectively. Specifically, we provide algorithms to show how to detect un-localizable nodes from a partially localizable network. Numerical simulation is provided to show the effectiveness of the developed method of computing positions

Changes in the Ecological Footprint of Rural Populations in the Taihang Mountains, China

Due to massive rural–urban migration, population size and age structure are subject to significant changes in the mountainous areas of China. This can influence the ecological pressure of the mountainous areas correspondingly. In particular, large numbers of young laborers migrate from rural areas, which may greatly decrease the intensity of local human activities. However, it is still unclear how population changes (size and age structure) affect environmental changes and how to measure these changes. We analyzed changes in the ecological footprint (EF) in the Taihang Mountain region in northern China using field survey data. From 2000 to 2016, the population size in the study area decreased by 9.7%, while the EF declined by 32.1%. The EF per capita (EF_per) decreased more rapidly with decreasing elevation, which indicated that at lower elevations, households were less dependent on local resources. For households with more elderly people, the EF_per was considerably lower than for other households in 2000. However, in 2016, this was not the case, and the households with a share of the working-age population between 50–75% had the lowest EF_per. Our study is of great practical significance for reasonably guiding population migration and rural sustainable development

Data from: Response of net primary production to land use and climate changes in the middle-reaches of the Heihe River basin

Net primary production (NPP) supplies matter, energy, and services to facilitate the sustainable development of human society and ecosystem. The response mechanism of NPP to land use and climate changes is essential for food security and biodiversity conservation but lacks a comprehensive understanding, especially in arid and semi-arid regions. To this end, taking the middle-reaches of the Heihe River basin (MHRB) as an example, we uncovered the NPP responses to land use and climate changes by integrating multi-source data (e.g., MOD17A3 NPP, land use, temperature, and precipitation) and multiple methods. The results showed that: (1) land use intensity (LUI) increasing, and climate warming and wetting promoted NPP. From 2000 to 2014, the LUI, temperature and precipitation of MHRB increased by 1.46, 0.58 °C and 15.76 mm, respectively, resulting in an increase of 14.62 gC/m2 in annual average NPP. (2) The conversion of low-yield cropland to forest and grassland increased NPP. Although the widespread conversion of unused land and grassland to cropland boosted both LUI and NPP, it was not conducive to ecosystem sustainability and stability due to huge water consumption and human-appropriated NPP. Urban sprawl occupied cropland, forest and grassland, and reduced NPP. (3) Increase in temperature and precipitation generally improved NPP. The temperature decreasing less than 1.2 °C also promoted the NPP of hardy vegetation due to the simultaneous precipitation increasing. However, warming-induced water stress compromised the NPP in arid sparse grassland and deserts. Cropland had greater NPP and NPP increase than natural vegetation due to the irrigation, fertilizers and other artificial inputs it received. Decrease in both temperature and precipitation generally reduced NPP, but the NPP in the well-protection or less-disturbance areas still increased slightly

NPP, Land Use and Meteorological Data

NPP, land use, land use intensity, and meteorological data of the Middle-Reaches of the Heihe River Basin in 2000 and 2014

Advancing the pressure sensing performance of conductive CNT/PDMS composite film by constructing a hierarchical-structured surface

Flexible pressure sensors have attracted wide attention due to their applications to electronic skin, health monitoring, and human-machine interaction. However, the tradeoff between their high sensitivity and wide response range remains a challenge. Inspired by human skin, we select commercial silicon carbide sandpaper as a template to fabricate carbon nanotube (CNT)/polydimethylsiloxane (PDMS) composite film with a hierarchical structured surface (h-CNT/PDMS) through solution blending and blade coating and then assemble the h-CNT/PDMS composite film with interdigitated electrodes and polyurethane (PU) scotch tape to obtain an h-CNT/PDMS-based flexible pressure sensor. Based on in-situ optical images and finite element analysis, the significant compressive contact effect between the hierarchical structured surface of h-CNT/PDMS and the interdigitated electrode leads to enhanced pressure sensitivity and a wider response range (0.1661 ​kPa−1, 0.4574 ​kPa−1 and 0.0989 ​kPa−1 in the pressure range of 0–18 ​kPa, 18–133 ​kPa and 133–300 ​kPa) compared with planar CNT/PDMS composite film (0.0066 ​kPa−1 in the pressure range of 0–240 ​kPa). The prepared pressure sensor displays rapid response/recovery time, excellent stability, durability, and stable response to different loading modes (bending and torsion). In addition, our pressure sensor can be utilized to accurately monitor and discriminate various stimuli ranging from human motions to pressure magnitude and spatial distribution. This study supplies important guidance for the fabrication of flexible pressure sensors with superior sensing performance in next-generation wearable electronic devices