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

Distribution, Sources, and Risk Assessment of Organochlorine Pesticides in Water from Beiluo River, Loess Plateau, China

The Loess Plateau has been a focus of public discussion and environmental concerns over the past three decades. In this study, in order to investigate the effect of OCP pollution in water of the Beiluo River, concentrations of 25 OCPs at 17 locations in the water were examined. The results showed that the concentration of ∑OCPs in the water ranged from 1.76 to 32.57 ng L−1, with an average concentration of 7.23 ng L−1. Compared with other basins in China and abroad, the OCP content in the Beiluo River was at a medium level. Hexachlorocyclohexane (HCH) pollution in the Beiluo River was mainly from the mixed input of lindane and technical HCHs. Dichlorodiphenyltrichloroethane (DDT) pollution was mainly from the mixed input of technical DDTs and dicofol. Most of the OCP pollution came from historical residues. The risk assessment results showed that hexachlorobenzene (HCB) and endosulfan had high ecological risks in the middle and lower reaches of the Beiluo River. Most residual OCPs were not sufficient to pose carcinogenic and non-carcinogenic health risks to humans. The results of this study can provide a reference for OCP prevention and control and watershed environmental management

Occurrence, Potential Risk Assessment, and Source Apportionment of Polychlorinated Biphenyls in Water from Beiluo River

Polychlorinated biphenyls (PCBs) are highly hazardous, persistent, and bioaccumulative substances that pose a threat to water quality in a number of locations, including the Beiluo River in Shaanxi Province, China. However, little is known about the contribution of PCBs to the Beiluo River. In this study, in order to look into the impact of sources on the water of the Beiluo River, the discovered PCB congeners in water were examined on a regional scale. The concentration of PCBs in water across Beiluo River was in the range from 0.065 to 1.92 ng L−1, and the average concentration was 0.37 ng L−1. The main PCB sources in the Beiluo River waterbody were found using positive matrix factorization (PMF). Source apportionment results indicated that the PCB pollution of the Beiluo River was mostly caused by industrial emissions, technical PCB mixtures, and coal and wood combustion. According to current ecological risk assessment guidelines, the PCB concentrations found in this study may have a negative impact on biological systems. Overall, the new information about the presence of several PCBs in the water of the Beiluo River justifies the need for urgent management actions, as well as long-term monitoring efforts, to protect ecosystems. Future investigations of these chemicals in China may use the conclusions of this first ecological risk level assessment on the PCB contamination in the waterbody of the Beiluo River as a guide

Distribution, Sources and Risk Assessment of Polychlorinated Biphenyls in Sediments from Beiluo River

The distribution and source of polychlorinated biphenyls (PCBs) pollution in the Beiluo River, the secondary tributary of the Yellow River, still remain unclear. With the purpose of determining the distribution, origins, and pollution levels of PCBs and their consequences on ecological risks, the concentrations of 27 PCBs at 17 locations in the sediments of the Beiluo River were examined in this study. The results showed that the mass concentrations of ∑PCBs in the sediment ranged from 0.12 to 1.25 ng∙g−1 (DW), with the highest point at sampling site B13 downstream of the river. Compared to most river sediments, both domestically and internationally, the concentration of PCBs in the sediment of the Beiluo River was at a low level, with 10-PCB and 6-PCB as the main components, indicating that the PCBs that are difficult to volatilise and degrade are more likely to remain in the sediment. The origins of PCBs in the sediments of the Beiluo River were examined by using positive matrix factorisation (PMF). The results revealed that the contamination of PCBs in the sediments of the Beiluo River mainly resulted from industrial emissions, technical PCB mixtures, and coal and wood combustion. The results of the ecological risk assessment indicated that PCBs in the sediments of the study area rarely contribute to adverse biological effects and the potential low risk to the environment

Magnetic graphene oxide nanocomposites: Nanoparticles growth mechanism and property analysis

The growth mechanism of magnetic nanoparticles (NPs) in the presence of graphite oxide (GO) has been investigated by varying the iron precursor dosage and reaction time (product donated as MP/GO). The synthesized magnetic NPs were anchored on the GO sheets due to the abundant oxygen-containing functionalities on the GO sheets such as carboxyl, hydroxyl and epoxy functional groups. The introduced NPs changed the intrinsic functionalities and lattice structure of the basal GO as indicated by FT-IR, Raman and XRD analysis, and this effect was enhanced by increasing the amount of iron precursor. Uniform distribution of NPs within the basal GO sheets and an increased particle size from 19.5 to 25.4, 31.5 and 85.4 nm were observed using scanning electron microscope (SEM) and transmission electron microscope (TEM) when increasing the weight ratio of GO to iron precursor from 10:1, to 5:1, 1:1 and 1:5, respectively. An aggregation of NPs was observed when increasing the iron precursor dosage or prolonging the reaction time from 1 to 8 h. Most functionalities were removed and the magnetic NPs were partially converted to iron upon thermal treatment under a reducing condition. The GO and MP/GO nanocomposites reacted for one and two hours (denoted as MP/GO1-1 h and MP/GO1-2 h) were converted from insulator to semiconductor after the annealing treatment as annealed GO (A-GO, 8.86 S cm-1), annealed MP/GO1-1 h (A-MP/GO1-1 h, 7.48 × 10-2 S cm-1) and annealed MP/GO1-2 h (A-MP/GO1-2 h, 7.58 × 10-2 S cm-1). The saturation magnetization was also enhanced significantly after the annealing treatment, increased from almost 0 to 26.7 and 83.6 emu g-1 for A-MP/GO1-1 h and A-MP/GO1-2 h, respectively. This journal i

Multi-fidelity optimization of a quiet propeller based on deep deterministic policy gradient and transfer learning

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Gut microbiota and microbiota-derived metabolites in cardiovascular diseases.

AbstractCardiovascular diseases, including heart failure, coronary artery disease, atherosclerosis, aneurysm, thrombosis, and hypertension, are a great economic burden and threat to human health and are the major cause of death worldwide. Recently, researchers have begun to appreciate the role of microbial ecosystems within the human body in contributing to metabolic and cardiovascular disorders. Accumulating evidence has demonstrated that the gut microbiota is closely associated with the occurrence and development of cardiovascular diseases. The gut microbiota functions as an endocrine organ that secretes bioactive metabolites that participate in the maintenance of cardiovascular homeostasis, and their dysfunction can directly influence the progression of cardiovascular disease. This review summarizes the current literature demonstrating the role of the gut microbiota in the development of cardiovascular diseases. We also highlight the mechanism by which well-documented gut microbiota-derived metabolites, especially trimethylamine N-oxide, short-chain fatty acids, and phenylacetylglutamine, promote or inhibit the pathogenesis of cardiovascular diseases. We also discuss the therapeutic potential of altering the gut microbiota and microbiota-derived metabolites to improve or prevent cardiovascular diseases

Replay-triggered brain-wide activation in humans

The consolidation of discrete experiences into a coherent narrative shapes the cognitive map, providing structured mental representations of our experiences. In this process, past memories are reactivated and replayed in sequence, fostering hippocampal-cortical dialogue. However, brain-wide engagement coinciding with sequential reactivation (or replay) of memories remains largely unexplored. In this study, employing simultaneous EEG-fMRI, we capture both the spatial and temporal dynamics of memory replay. We find that during mental simulation, past memories are replayed in fast sequences as detected via EEG. These transient replay events are associated with heightened fMRI activity in the hippocampus and medial prefrontal cortex. Replay occurrence strengthens functional connectivity between the hippocampus and the default mode network, a set of brain regions key to representing the cognitive map. On the other hand, when subjects are at rest following learning, memory reactivation of task-related items is stronger than that of pre-learning rest, and is also associated with heightened hippocampal activation and augmented hippocampal connectivity to the entorhinal cortex. Together, our findings highlight a distributed, brain-wide engagement associated with transient memory reactivation and its sequential replay

Positive and negative magnetoresistance phenomena observed in magnetic electrospun polyacrylonitrile-based carbon nanocomposite fibers

Unique temperature dependent resistance behavior (positive/negative temperature coefficient switching at 240 K), and tunable negative and positive magnetoresistance switching phenomena were observed in the magnetic carbon nanocomposite fibers prepared from heat treatment of the nitrate soaked oxidation stabilized polyacrylonitrile (PAN) nanofibers. The physical mechanisms were revealed by considering the variable range hopping electron transportation model, electron quantum interference and spin-dependent scattering effects. © 2013 The Royal Society of Chemistry