The symport of lactose and H+ is an important physiological process in E. coli, for it is closely related to cellular energy supply. In this paper, we review, extend and analyse a newly proposed ...cotransport model that takes the "leakage" phenomenon (uncoupled particle translocation) into account and also satisfies the static head equilibrium condition. Then, we use the model to study the equilibrium properties, including equilibrium solution and the time required to reach equilibrium, of the symport process of E. coli LacY protein, when varying the parameters of the initial state of cotransport system. It can be found that in our extended model, H+ and lactose will reach their equilibrium state separately, and when "leakage" exists, it linearly affects the equilibrium solution, which is a useful property that the original model does not have. We later investigated the effect of the volume of periplasm and cytoplasm on the equilibrium properties. For a certain E. coli cell, as it continues to lose water and contract, the time for cytoplasm pH to be stabilized by symport increases monotonically when the cell survives. Finally, we reproduce the experimental data from a literature to verify the validity of the extension in this symport process. The above phenomena and other findings in this paper may help us to not only further validate or improve the model, but also deepen our understanding of the cotransport process of E. coli LacY protein.
We consider a class of popular distributed non-convex optimization problems, in which agents connected by a network ς collectively optimize a sum of smooth (possibly non-convex) local objective ...functions. We address the following question: if the agents can only access the gradients of local functions, what are the fastest rates that any distributed algorithms can achieve, and how to achieve those rates. First, we show that there exist difficult problem instances, such that it takes a class of distributed first-order ' methods at least O(1/√(ξ(ς)) × L̅/ε) communication rounds to achieve certain e-solution where ξ(ς) denotes the spectral gap of the graph Laplacian matrix, and L is some Lipschitz constant. Second, we propose (near) optimal methods whose rates match the developed lower rate bound (up to a ploylog factor). The key in the algorithm design is to properly embed the classical polynomial filtering techniques into modern first-order algorithms. To the best of our knowledge, this is the first time that lower rate bounds and optimal methods have been developed for distributed non-convex optimization problems.
Photocatalysts with excellent performance, low cost and innocuity are highly desired for environmental remediation. Zero-dimensional carbon dots with a size of 2–10 nm represent a class of promising ...co-catalysts due to their excellent photo-induced electron transfer, increased light absorption and thus boosted photocatalytic activity. Herein, carbon dots/high-crystalline g-C
3
N
4
(CDs/H-CN) composites were successfully prepared via a facile calcination method for the degradation of tetracycline (TC) under visible light irradiation. Experimental results reveal that the CDs/H-CN-1 composite displays the optimal photocatalytic degradation of TC (86%, 120 min), and exhibits remarkable photostability (no decrease after 4 cycles of reaction within 480 min). According to the identification of intermediates by liquid chromatography-mass spectrometry (LC–MS) analysis, the degradation pathways of TC were proposed. In addition, the planting experiment of mung beans was performed to further confirm the biotoxicity of TC degraded products. This work underlines the importance of co-catalyst and presents a feasible protocol for the rational construction of H-CN-based photocatalysts for various photocatalytic applications.
Graphic abstract
We present a microwave method for the dielectric characterization of small liquids based on a metamaterial-based sensor The proposed sensor consists of a micro-strip line and a double split-ring ...resonator (SRR). A large electric field is observed on the two splits of the double SRRs at the resonance frequency (1.9 GHz). The dielectric property data of the samples under test (SUTs) were obtained with two measurements. One is with the sensor loaded with the reference liquid (REF) and the other is with the sensor loaded with the SUTs. Additionally, the principle of extracting permittivity from measured changes of resonance characteristics changes of the sensor loaded with REF and SUTs is given. Some measurements were carried out at 1.9 GHz, and the calculated results of methanol⁻water mixtures with different molar fractions agree well with the time-domain reflectometry method. Moreover, the proposed sensor is compact and highly sensitive for use of sub-wavelength resonance. In comparison with literature data, relative errors are less than 3% for the real parts and 2% for the imaginary parts of complex permittivity.
The sintering of supported metal nanoparticles is a major route to the deactivation of industrial heterogeneous catalysts, which largely increase the cost and decrease the productivity. Here, we ...discover that supported palladium/gold/platinum nanoparticles distributed at the interface of oxide supports and nitrogen-doped carbon shells would undergo an unexpected nitrogen-doped carbon atomization process against the sintering at high temperatures, during which the nanoparticles can be transformed into more active atomic species. The in situ transmission electron microscopy images reveal the abundant nitrogen defects in carbon shells provide atomic diffusion sites for the mobile atomistic palladium species detached from the palladium nanoparticles. More important, the catalytic activity of sintered and deactivated palladium catalyst can be recovered by this unique N-doped carbon atomization process. Our findings open up a window to preparation of sintering-resistant single atoms catalysts and regeneration of deactivated industrial catalysts.
The large-scale consumption and discharge of antibiotic tetracycline (TC) urge us to search for a highly efficient and eco-friendly technology to remove it. In this work, face-contact ZnSnO
3
@g-C
3
...N
4
core–shell heterojunction was successfully constructed via one-step calcination route. The experimental data indicate that the photocatalytic TC removal performance of ZnSnO
3
@g-C
3
N
4
(1:3) reaches 90.8% within 120 min under the same condition compared with bulk g-C
3
N
4
(32% degradation) and ZnSnO
3
(9% degradation). The improved photocatalytic activity is ascribed to the formation of core–shell structure between ZnSnO
3
and g-C
3
N
4
which not only enlarges visible light response but also effectively separates electron–hole pairs. Meanwhile, this face-contact ZSO-CN photocatalyst displays much more contact interfaces than the point-contact ZSO-CN photocatalyst, and the contact interfaces could play the part of efficient channels for charge transfer. Finally, the photocatalytic reaction mechanism on ZnSnO
3
@g-C
3
N
4
was also stated at length through active species capture and electron spin resonance (ESR) tests. And the possible intermediates products were discussed through the liquid chromatography–mass spectrometry (LC–MS) analysis.
Assessing biochar's ability to resist oxidation is fundamental to understanding its potential to sequester carbon. Chemical oxidation exhibits good performance in estimating the oxidation resistance ...of biochar. Herein, oxidation resistance of 14 types of biochars produced from four feedstocks at different pyrolysis conditions (hydrothermal versus thermal carbonization) was investigated via hydrogen peroxide oxidation with varying concentrations. The oxidation resistance of organic carbon (C) of hydrochars was relatively higher than that of 250°C pyrochars (P250) but was comparable to that of 450°C pyrochars (P450). Both hydrochars and P450 from ash-rich feedstocks contained at least three different C pools (5.9–18.3% labile, 43.2–56.5% semi-labile and 26.9–45.9% stable C). Part (<33%) of aromatic C within 600°C pyrochars (P600) was easily oxidizable, which consisted of amorphous C. The influence of pyrolysis temperature upon oxidation resistance of biochars depended on the feedstock. For ash-rich feedstock (rice straw, swine manure and poultry litter), the oxidation resistance of biochars was determined by both aromaticity and mineral components, and mineral protection was regulated by pyrolysis conditions. The amorphous silicon within hydrochars and P450 could interact with C, preventing C from being oxidized, to some extent. Nevertheless, this type of protection did not occur for P250 and P600.
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•Oxidation resistance of biochar was studied using H2O2 with varying concentrations.•Hydrochar showed higher oxidation resistance than low temperature pyrochar.•Impact of temperature upon oxidation resistance of pyrochar depended on feedstock.•Oxidation resistance of ash-poor biochar was mainly regulated by aromaticity.•Oxidation resistance of ash-rich biochar was also affected by mineral encapsulation.
Photodegradation and biodegradation of pyrogenic dissolved organic matter (pyDOM) play crucial roles in regulating greenhouse gas emissions and stabilizing organic matter. In this study, we conducted ...a 56-day microbial laboratory incubation to investigate the biodegradation patterns of pristine and photobleached pyDOM leached from a thermal series of chars (300, 450, and 600 °C) based on FT-ICR-MS, gas analysis, N speciation, and 16S rDNA sequencing. As the pyrolysis temperature increased, the among of biomineralized carbon of pyDOM decreased, while the molecular diversity and aromaticity increased. Photobleaching increased the among of biomineralized carbon of pyDOM from 40%–70% to 60%–80%, but decreased the molecular diversity, molecular weight, and aromaticity, with a major removal of lignin-like compounds. Microbial incubation lowered the molecular diversity but increased the molecular weight and aromaticity of both pristine and photobleached samples. Tannin-like structures, carbohydrates, and aliphatic/protein were preferentially biodegraded, while lipid, lignin-like structures, unsaturated hydrocarbons, and condensed aromatics were more likely to be preserved or newly produced. The photobio-resistant components were mainly comprised of lignin-like and tannin-like structures. Photobleached pyDOM samples released more CO2 but less N2O, as they may possess high denitrification rate due to their high carbon reactivity. The bacterial richness and diversity in pyDOM were lower than the original inoculum. In addition, distinct differences were noted between the bacterial community structure of the original inoculum and that of pristine and photobleached pyDOM samples following various incubation times. Specifically, proteobacteria was increased and remained the predominant phylum in all pyDOM solutions compared to the original inoculum, while Actinobacteriota, Bdellovibrionota, Firmicutes, or Nitrospirota phyla were increased in several samples either after 7 or 56 days of incubation. In particular, photobleached pyDOM pyrolyzed at 600 °C exhibited the strongest filtration effects on the bacterial microflora. These results help to elucidate the biogeochemical cycling and turnover of pyDOM in sunlit and dark aquatic environments such as fluvial and groundwater networks, lakes, and the ocean.
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•Photobleached pyDOM of lower pyrolysis temperature had higher biodegradability.•Incubation lowered the molecular diversity but increased the aromaticity of pyDOM.•Photobio-resistant components mainly comprised lignin- and tannin-like structures.•Photobleached pyDOM released more CO2 but less N2O than pristine pyDOM.•PyDOM sources and incubation time regulated bacterial succession.
The association of organic carbon (OC) with ferrihydrite (Fh) is critical for regulating soil carbon persistence. However, the reduction of Fh compromises the stability of Fh-bound OC. So far, little ...is known about the impact of formation pathway (adsorption versus coprecipitation) of Fh-OC association (FOA) on the mobilization of Fh-bound OC during Fh reduction. In this study, we examined the release of Fh-adsorbed and Fh-coprecipitated OC during the abiotic reduction of FOA by hydroxylamine hydrochloride, to elucidate processes regulating the stability of OC during the redox processes. Using ESI-FT-ICR-MS, combustion-derived condensed polycyclic aromatic and vascular plant-derived polyphenols were found to be preferentially adsorbed and coprecipitated by Fh compared with aliphatics, and this structural preference was more pronounced for adsorption. Adsorbed and coprecipitated OC showed different release patterns during reduction: all the adsorbed OC was rapidly released initially, while the coprecipitated OC was slowly mobilized for almost the entire reduction period. The reductive release of OC depended upon the C/Fe ratio, with high C/Fe ratio inhibiting the release of OC. For both adsorption and coprecipitation, aliphatics were preferentially released from FOA into solution during Fe reduction. Our results are valuable for a better understanding of the role of Fh in OC stabilization in natural environments with fluctuating redox conditions.
•Reductive release of ferrihydrite - adsorbed and -co-precipitated DOC was tested.•Adsorbed and co-precipitated OC showed different release patterns during ferrihydrite reduction.•Ferrihydrite preferentially associated with aromatics compared with aliphatics.•Aliphatics were preferentially reductively released during Fe reduction.
Herein, a unique 0D/2D nanodiamonds (NDs)/hematite (Fe
2
O
3
) composite photocatalyst was constructed by the solvothermal method and then was used to remove tetracycline pollutants in the aqueous ...solution, where the NDs nanoparticles were tightly anchored on the surface of hexagonal Fe
2
O
3
nanosheets. The superior photocatalytic performance (85%, 180 min) was obtained by the optimum 15-NDs/Fe
2
O
3
composite sample (containing 15 wt% NDs), which is approximately 4.13 times higher than that of pure Fe
2
O
3
. This is because the introduction of NDs nanoparticles not only promotes the visible-light absorption of Fe
2
O
3
, but also facilitates the separation of photogenerated electrons and holes in the interface of composite by the design of Z-scheme heterostructure. Besides, the intermediates, active species and reaction mechanism in the photocatalytic process were also discussed. This work enriches the knowledge in designing of novel 0D/2D Z-scheme heterojunction composites for photocatalysis.
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