Flame dynamics and statistics of mixed supersonic and subsonic combustion modes under different air inflow and global equivalence ratio conditions in a hydrogen-fueled model combustor are numerically ...studied. Three methods including spanwise-averaged Mach number, spanwise-averaged Mach number conditioning on the local heat release, and fraction of heat release are proposed to identify supersonic and subsonic combustion modes. The probability distributions of supersonic and subsonic combustion modes are also analyzed based on the statistics on multiple instantaneous snapshots of the numerical results. The critical global equivalence ratio for thermal choking in a range of supersonic inflow conditions is derived theoretically based on a one-dimensional duct flow with heat addition. Furthermore, it is found that the flame lift-off distance in both supersonic and subsonic flows decreases with increased air inflow velocity, but increases with global equivalence ratio. The fraction of supersonic heat release and its oscillation increase with increased air inflow velocity.
•Three methods are proposed to quantify the supersonic and subsonic combustion modes.•Probability distributions of supersonic and subsonic combustion modes are presented.•Critical global equivalence ratio for thermal choking of supersonic inflow is derived.•Flame lift-off distance in both supersonic and subsonic flows are quantified.
•Autoignition and propagation of supersonic ethylene flame is investigated numerically.•The time scale and energy balance methods are developed to study flame stabilization.•The two methods show good ...validity in the autoignition process of the ethylene flame.•Premixed combustion mode is dominant during the flame autoignition process.•Diffusion combustion mode is dominant when the flame is finally stabilized.
Two analysis methods for time scale and energy balance relevant to flame ignition and stabilization in cavity-stabilized flames are developed. The interaction time of hot product in the recirculation zone of the cavity with the surrounding unburned mixture and the reaction induction time of the mixture are estimated in the time scale method. The energy release from chemical reactions and the energy loss due to species exchange in the recirculation zone are included in the energy balance method. The autoignition and propagation of supersonic ethylene flames in a model supersonic combustor with a cavity is investigated first using highly resolved large eddy simulation. The evolutions of the two time scales are then calculated in the ignition process of the supersonic ethylene flames. It is found that the time scale theory is well valid in the flame propagation and stabilization stages. The rates of energy generation and loss are then analyzed in the cavity. It is found that initially the local energy generation rate is relatively small, resulting in slow net energy accumulation in the cavity. Then the energy generation increases due to the intermittent flame propagation in the cavity, whereas the energy loss oscillates consistently since the burned gas leaves the cavity. Also, energy generation and loss are generally balanced in the cavity and all tend to zero after the flame is globally stabilized. The two methods present the characteristic time scales and energy balancing during the transient ignition process for the first time.
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•We for the first time apply the unique hyperspectral stimulated Raman scattering (SRS) imaging technique to quantitatively assess and monitor the bioaccumulations and metabolic ...toxicities of micro- and nano- plastics pollutions in live zebrafish during their early developmental stages.
Microplastics (MP) and nanoplastics (NP) pollutions pose a rising environmental threat to humans and other living species, given their escalating presence in essential resources that living subjects ingest and/or inhale. Herein, to elucidate the potential health implications of MP/NP, we report for the first time by using label-free hyperspectral stimulated Raman scattering (SRS) imaging technique developed to quantitatively monitor the bioaccumulation and metabolic toxicity of MP/NP within live zebrafish larvae during their early developmental stages. Zebrafish embryos are exposed to environmentally related concentrations (3–60 μg/ml) of polystyrene (PS) beads with two typical sizes (2 μm and 50 nm). Zebrafish are administered isotope-tagged fatty acids through microinjection and dietary intake for in vivo tracking of lipid metabolism dynamics. In vivo 3D quantitative vibrational imaging of PS beads and intrinsic biomolecules across key zebrafish organs reveals that gut and liver are the primary target organs of MP/NP, while only 50 nm PS beads readily aggregate and adhere to the brain and blood vessels. The 50 nm PS beads are also found to induce more pronounced hepatic inflammatory response compared to 2 μm counterparts, characterized by increased biogenesis of lipid droplets and upregulation of arachidonic acid detected in zebrafish liver. Furthermore, Raman-tagged SRS imaging of fatty acids uncovers that MP/NP exposure significantly reduces yolk lipid utilization and promotes dietary lipid storage in zebrafish, possibly associated with developmental delays and more pronounced food dilution effects in zebrafish larvae exposed to 2 μm PS beads. The hyperspectral SRS imaging in this work shows that MP/NP exposure perturbs the development and lipid metabolism in zebrafish larvae, furthering the understanding of MP/NP ingestions and consequent toxicity in different organs in living species.
Osmotic power, also known as 'blue energy', is produced by mixing solutions of different salt concentrations, and represents a vast, sustainable and clean energy source. The efficiency of harvesting ...osmotic power is primarily determined by the transmembrane performance, which is in turn dependent on ion conductivity and selectivity towards positive or negative ions. Atomically or molecularly thin membranes with a uniform pore environment and high pore density are expected to possess an outstanding ion permeability and selectivity, but remain unexplored. Here we demonstrate that covalent organic framework monolayer membranes that feature a well-ordered pore arrangement can achieve an extremely low membrane resistivity and ultrahigh ion conductivity. When used as osmotic power generators, these membranes produce an unprecedented output power density over 200 W m
on mixing the artificial seawater and river water. This work opens up the application of porous monolayer membranes with an atomically precise structure in osmotic power generation.
We report an Ag1 single‐atom catalyst (Ag1/MnO2), which was synthesized from thermal transformation of Ag nanoparticles (NPs) and surface reconstruction of MnO2. The evolution process of Ag NPs to ...single atoms is firstly revealed by various techniques, including in situ ETEM, in situ XRD and DFT calculations. The temperature‐induced surface reconstruction process from the MnO2 (211) to (310) lattice plane is critical to firmly confine the existing surface of Ag single atoms; that is, the thermal treatment and surface reconstruction of MnO2 is the driving force for the formation of single Ag atoms. The as‐obtained Ag1/MnO2 achieved 95.7 % Faradic efficiency at −0.85 V vs. RHE, and coupled with long‐term stability for electrochemical CO2 reduction reaction (CO2RR). DFT calculations indicated single Ag sites possessed high electronic density close to Fermi Level and could act exclusively as the active sites in the CO2RR. As a result, the Ag1/MnO2 catalyst demonstrated remarkable performance for the CO2RR, far surpassing the conventional Ag nanosized catalyst (AgNP/MnO2) and other reported Ag‐based catalysts.
Silver nanoparticles converted into single atoms bring about a significant improvement in electrocatalytic CO2 reduction with a 95.7 % faradic efficiency for CO production.
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•Carboxyl functionalized Ti3C2Tx MXene (TCCH) was synthesized.•The stability of the TCCH in water was significantly improved compared with raw Ti3C2Tx.•The optimized TCCH showed ...superior U(VI) and Eu(III) adsorption capacities up to 334.8 mg/g and 97.1 mg/g, respectively.•The adsorption mechanism was associated with inner-sphere surface complexation and electrostatic interaction.
With the development of nuclear power, the negative environmental impact such as radioactive pollution has become an urgent issue to impede the utilization of nuclear energy. The construction of promising organic-inorganic hybrid materials is considered as an effective strategy for environmental remediation of radioactive contamination. In this work, two-dimensional transition metal carbide (MXene), an emerging inorganic layered material, has been successfully modified by carboxyl terminated aryl diazonium salt to both enhance its chelating ability to radionuclides and improve its water stability. The carboxyl functionalized Ti3C2Tx MXene (TCCH) shows excellent removal ability for U(VI) and Eu(III), evidenced by ultrafast adsorption kinetics (3 min), high maximum adsorption capacities (344.8 mg/g for U and 97.1 mg/g for Eu) and high removal percentage of radionuclides from artificial groundwater (> 90%). The adsorption of U(VI) and Eu(III) on TCCH are in good accord with the Langmuir adsorption isotherm model and the pseudo-second-order kinetic model. Ionic strength experiments, X-ray photoelectron spectroscopy (XPS) and Extended X-ray absorption fine structure (EXAFS) analyses were conducted to assess the detailed adsorption mechanism. The results reveal that the adsorption of U(VI) on TCCH follows an inner-sphere configuration, whereas the adsorption of Eu(III) is determined by both inner-sphere complexation and electrostatic interaction.
The synthesis of single‐atom catalysts and the control of the electronic properties of catalytic sites to arrive at superior catalysts is a major challenge in heterogeneous catalysis. A stable ...supported single‐atom silver catalyst with a controllable electronic state was obtained by anti‐Ostwald ripening. An electronic perturbation of the catalytic sites that is induced by a subtle change in the structure of the support has a strong influence on the intrinsic reactivity. The higher depletion of the 4d electronic state of the silver atoms causes stronger electronic metal–support interactions, which leads to easier reducibility and higher catalytic activity. These results may improve our understanding of the nature of electronic metal–support interactions and lead to structure–activity correlations.
Electronic metal–support interactions (EMSI): A supported single‐atom silver catalyst with a controllable electronic state has been developed. An electronic perturbation of the catalytic sites that is induced by subtle changes in the structure of the support has a crucial influence on the intrinsic reactivity of the catalyst.
CRISPR-Cas9 systems are bacterial adaptive immune systems that defend against infection by phages. Through the RNA-guided endonuclease activity of Cas9 they degrade double-stranded DNA with a ...protospacer adjacent motif (PAM) and sequences complementary to the guide RNA. Recently, two anti-CRISPR proteins (AcrIIA2 and AcrIIA4 from Listeria monocytogenes prophages) were identified, both of which inhibit Streptococcus pyogenes Cas9 (SpyCas9) and L. monocytogenes Cas9 activity in bacteria and human cells. However, the mechanism of AcrIIA2- or AcrIIA4-mediated Cas9 inhibition remains unknown. Here we report a crystal structure of SpyCas9 in complex with a single-guide RNA (sgRNA) and AcrIIA4. Our data show that AcrIIA2 and AcrIIA4 interact with SpyCas9 in a sgRNA-dependent manner. The structure reveals that AcrIIA4 inhibits SpyCas9 activity by structurally mimicking the PAM to occupy the PAM-interacting site in the PAM-interacting domain, thereby blocking recognition of double-stranded DNA substrates by SpyCas9. AcrIIA4 further inhibits the endonuclease activity of SpyCas9 by shielding its RuvC active site. Structural comparison reveals that formation of the AcrIIA4-binding site of SpyCas9 is induced by sgRNA binding. Our study reveals the mechanism of SpyCas9 inhibition by AcrIIA4, providing a structural basis for developing 'off-switch' tools for SpyCas9 to avoid unwanted genome edits within cells and tissues.
Silver chains fabricated from supported silver particles were embedded in Hollandite‐type manganese oxide, thereby exposing single silver atoms as catalytically active sites (see picture). Excellent ...oxygen activation and high catalytic activity in the oxidation of formaldehyde was observed.
Monacolin K (MK) is the principal active substance in Monascus-fermentation products (e.g. red yeast rice). MK is effective in reducing cholesterol levels in humans and has been widely used as a ...lipid-lowering drug. The mechanism for this is through a high degree of competitive inhibition of the rate-limiting enzyme HMG-CoA reductase (HMGR) in the cholesterol synthesis pathway. In addition to lowering blood lipid levels, MK also prevents colon cancer, acute myeloid leukemia and neurological disorders such as Parkinson's disease and type I neurofibromatosis. The aim of this manuscript is to comprehensively review the progress in the study of the biological activity of MK and its imechanism of action in reducing blood lipid concentration, prevention of cancer and its neuroprotective, anti-inflammatory and antibacterial properties. This review provides a reference for future applications of MK in functional foods and medicine.
•Monacolin K (MK) is effective in reducing cholesterol levels in humans.•The lipid-lowering mechanism of MK is the highly competitive inhibition of HMGR.•The anti-cancer effect of MK and its mechanism are summarized.•MK also has neuroprotective, anti-inflammatory and antibacterial effects.
