There are more than 1000 microbial species living in the complex human intestine.The gut microbial community plays an important role in protecting the host against pathogenic microbes,modulating ...immunity,regulating metabolic processes,and is even regarded as an endocrine organ.However,traditional culture methods are very limited for identifying microbes.With the application of molecular biologic technology in the field of the intestinal microbiome,especially metagenomic sequencing of the next-generation sequencing technology,progress has been made in the study of the human intestinal microbiome.Metagenomics can be used to study intestinal microbiome diversity and dysbiosis,as well as its relationship to health and disease.Moreover,functional metagenomics can identify novel functional genes,microbial pathways,antibiotic resistance genes,functional dysbiosis of the intestinal microbiome,and determine interactions and co-evolution between microbiota and host,though there are still some limitations.Metatranscriptomics,metaproteomics and metabolomics represent enormous complements to the understanding of the human gut microbiome.This review aims to demonstrate that metagenomics can be a powerful tool in studying the human gut microbiome with encouraging prospects.The limitations of metagenomics to be overcome are also discussed.Metatranscriptomics,metaproteomics and metabolomics in relation to the study of the human gut microbiome are also briefly discussed.
Intensive anthropogenic activity has triggered serious heavy metal contamination of soil. Land use and land cover (LULC) changes bear significant impacts, either directly or indirectly, on the ...distribution of heavy metal in soils. A total of 180 samples were acquired from various land covers at different depths, namely surface soils (020 cm) and subsurface soils (20–40 cm). Spatial interpolation, geographically weighted regression (GWR) and self-organizing map (SOM) were used to discern how variations in the spatial distributions of soil heavy metals were caused by human activities for different land uses, and how these pollutants contributed to environmental risks. The medium concentrations of Cd, Cr, Cu, Pb and Zn in surface soil all exceeded the corresponding local background values in flat cropland and developed area soil. The overall ecological risk level of the study varied from low to medium. The GWR model indicated that the land use intensity had a certain influence on the accumulation of heavy metals in the surface soil. K-means clustering of the SOM revealed that the type of LULC also contributed to the redistribution of heavy metals in the surface soil.
Display omitted
•Heavy metal differentiation in soil was described by spatial interpolation.•The correlation between heavy metals and land use intensity was analyzed.•Most of samples from cropland and developed areas were polluted by heavy metals.•SOM was used to identify the impact of LULC on heavy metal accumulation in soil.
Changes in land use and land cover caused by human activities affect the enrichment and redistribution of heavy metals in soil.
To dramatically stabilize the nanostructure of Sn and achieve ultrahigh reversibility of conversion reactions in lithiated SnO2, a series of SnO2–transition metal–graphite ternary nanocomposites are ...produced by ball milling, demonstrating high initial Coulombic efficiencies up to 88.6%, high reversible capacity (>700 mAh g−1 at 2 A g−1), and ultralong cycling life (90.3% of capacity retention after 1300 cycles).
Traditionally, the factorization method is applied to reconstruct the 3D geometry of a target from its sequential inverse synthetic aperture radar images. However, this method requires performing ...cross-range scaling to all the sub-images and thus has a large computational burden. To tackle this problem, this paper proposes a novel method for joint cross-range scaling and 3D geometry reconstruction of steadily moving targets. In this method, we model the equivalent rotational angular velocity (RAV) by a linear polynomial with time, and set its coefficients randomly to perform sub-image cross-range scaling. Then, we generate the initial trajectory matrix of the scattering centers, and solve the 3D geometry and projection vectors by the factorization method with relaxed constraints. After that, the coefficients of the polynomial are estimated from the projection vectors to obtain the RAV. Finally, the trajectory matrix is re-scaled using the estimated rotational angle, and accurate 3D geometry is reconstructed. The two major steps, i.e., the cross-range scaling and the factorization, are performed repeatedly to achieve precise 3D geometry reconstruction. Simulation results have proved the effectiveness and robustness of the proposed method.
Rare earth elements (REEs) have been increasingly emitted into the atmosphere with a worldwide increase in use of these metals. However, the research on REEs in atmospheric particulates is fairly ...limited. In this paper, atmospheric particulates including total suspended particulate (TSP) matter and particles with an equivalent aerodynamic diameter less than 10 μm (PM10) were collected around a rare earth mine tailing in Baotou, the largest rare earth industrial base in China, in August 2012 and March 2013, for the analyses of REE levels and distributions. The total concentrations of REEs for TSP were 172.91 and 297.49 ng/m3, and those for PM10 were 63.23 and 105.52 ng/m3, in August 2012 and March 2013, respectively. Enrichment factors for all 14 analyzed REEs in the TSP and PM10 indicated that the REE enrichment in atmosphere particulates was caused by anthropogenic sources and influenced by the strong wind in spring season. The spatial distribution of REEs in TSP showed a strong gradient in the prevailing wind direction. The chondrite-normalized patterns of REEs in TSP and PM10 were similar with the conspicuous fractionation between light REEs and heavy REEs.
This paper investigates the performance limits of cognitive-uplink fixed satellite service (FSS) and terrestrial fixed service (FS) operating in the range 27.5-29.5 GHz for Ka-band. In light of ...standard recommendations from the International Telecommunications Union and a rain-fading channel model, we analyze the interference level at the FS receiver by considering statistical properties of the channel, propagation losses, and antenna patterns. By employing the interference constraint criterion at the FS, an analytical expression for the capacity of the cognitive-uplink FSS is derived, which is useful in understanding the limits in performance and the potential application of the considered coexistence scenario. Simulations are carried out to verify the theoretical derivations and highlight the impact of key parameters on the performance limits.
Diverse late transition metal catalysts convert terminal or internal alkynes into transient allylmetal species that display electrophilic or nucleophilic properties. Whereas classical methods for the ...generation of allylmetal species often form stoichiometric by‐products, the recent use of alkynes as allylmetal precursors enables completely atom‐efficient catalytic processes to be carried out, including enantioselective transformations.
The best of both worlds: Diverse late transition metal catalysts can convert terminal or internal alkynes into transient allylmetal species that display electrophilic or nucleophilic properties. The use of alkynes as allylmetal precursors enables completely atom‐efficient catalytic processes to be carried out, including enantioselective transformations.
► Products from fast pyrolysis of cellulose include pyrans, furans and linear small molecular compounds. ► Cellubiose and glucose have higher furans content and lower pyrans content. ► Furfural is ...the product from 5-hydroxymethyl furfural decomposition. ► The results from density functional theory studies confirm and explain the experimental results. ► The reaction pathways of cellulose pyrolysis are deduced and a modified mechanism model is also proposed.
The mechanism of fast pyrolysis of cellulose has been studied by using an analytical pyrolyzer coupled with a gas chromatography–mass spectrometry set-up (Py-GC/MS). The results showed that the main products comprised pyrans such as levoglucosan and levoglucosenone, furans such as furfural and 5-hydroxymethyl furfural, and linear small molecular chemicals such as acetaldehyde and 1-hydroxy-2-propanone. The compositions of products from fast pyrolysis of cellubiose and glucose were similar to that from cellulose, but with higher furan contents and lower pyran contents. Based on the experimental results, density functional theory (DFT) studies were carried out to deduce the pyrolysis mechanism of cellulose. The results showed the formation of 5-hydroxymethyl furfural from d-glucopyranose unit to be easier than the formation of levoglucosan, in agreement with the experimental results. The deduced mechanism of reaction pathways in cellulose pyrolysis provides insight into the pyrolysis behavior of cellulose and allows modification of previously proposed related mechanisms.
•Rare earth elements has influence on P adsorption process in soil.•P adsorption declined when soils were amended with lower concentration rare earth.•Langmuir equation fitted P adsorption in all ...five types soils.•P desorption increased when soil were amended with rare earth.
Phosphorus (P) is an important biogeochemical element and the environmental fate of P receives increasing attention. Through batch equilibration experiments, the adsorption and desorption of P in the absence and presence of exogeneous rare earth elements (REEs) were investigated in five types of agricultural soil samples collected from China. The results showed that the addition of different doses of REEs had influences on P adsorption processes in the soils, and there were differences in different soil types and different P concentrations of the P solutions. The amount of P adsorption tended to decline when the five types of soils were amended with low concentrations of REEs. The characteristics of P adsorption were more complicated when high concentrations of REEs were added to the different soils. Affected by the high concentrations of REEs, when the P concentration of the P solution added to soils was less than 20mgL−1, the rate of P adsorption tended to increase in all the five types of soils. However, when the P concentration of the P solution added to soil was greater than 30mgL−1, the rate of P adsorption tended to decrease. The Langmuir equation fitted P adsorption in all the five types of soils well. Compared with the control, when soil samples were amended with REEs, the P desorption rates of the five types of soils increased.
The development of novel polymerization capable of yielding polymers with low molecular weight distribution (Đ) is essential and significant in polymer chemistry, where monofunctional initiator ...contains only one initiation site in these polymerizations generally. Here, ketyl radical anion species is introduced to develop a novel Ketyl Mediated Polymerization (KMP), which enables radical polymerization at carbon radical site and anionic ring‐opening polymerization at oxygen anion site, respectively. Meanwhile, polymerization and corresponding organic synthesis generally couldn't be performed simultaneously in one pot. Through KMP, organic synthesis and polymerization are achieved in one pot, where small molecules (cyclopentane derivates) and polymers with low Đ are successfully prepared under mild condition simultaneously. At the initiation step, both organic synthesis and polymerization are initiated by single electron transfer reaction with ketyl radical anion formation. Cyclopentane derivates are synthesized through 3–3 coupling reaction and cyclization. Polystyrene and polycaprolactone with low Đ and a full monomer conversion are prepared by KMP via radical polymerization and anionic ring‐opening polymerization, respectively. This work therefore enables both organic synthesis and two different polymerizations from same initiation system, which saves time, labour, resource and energy and expands the reaction mode and method libraries of organic chemistry and polymer chemistry.
One ketyl radical anion can enable a 3–3 coupling reaction, radical polymerization at a carbon radical site, and anionic ring‐opening polymerization at an oxygen anion site. This results in simultaneous organic synthesis and polymerization in one pot; thereby cyclopentane derivates and polymers with low Đ are successfully prepared under mild conditions.
PDF
