356 research outputs found
Simulation of the calcination of a core-in-shell CuO/CaCO 3 particle for CaâCu chemical looping
The internal heat balance through heat generation due to CuO reduction and its consumption by CaCO3 decomposition makes calcination a critical step in a novel CaâCu chemical looping process (CaLâCLC). Thus, the calcination behaviour of composite Ca/Cu particles needs to be well understood, especially taking into account that mismatching of heat generation and consumption in the particles can lead to local superheating, agglomeration and loss of activity due to enhanced sintering. In this work, a composite particle model was developed to study the calcination behaviour within a spherical core-in-shell type of particle containing grains of CuO and CaCO3. Simulation results showed that ambient temperature, shell porosity, particle size, and CaCO3 grain size significantly affected the CuO and CaCO3 reaction processes, while the impact of initial particle temperature and CuO grain size can be ignored in the range of parameters considered in the study. By comparison of different types of particles, it was concluded that the core-in-shell pattern was more advantageous if such particles are being applied in CaLâCLC cycles due to better matching in reaction kinetics resulting in more stable and uniform particle temperature distribution during the calcination stage
Compatibility of NiO/CuO in CaâCu chemical looping for highâpurity H2 production with CO2 capture
CaâCu chemical looping is a novel and promising approach in converting methane into pure H2 following the principle of sorptionâenhanced reforming. Its operational efficiency is largely determined by an appropriate coexistence of Cuâbased oxygen carriers and Niâbased catalysts. In this work, NiO/CuO composites were synthesized and their catalytic activity for H2 production was measured using a fixedâbed reactor system equipped with an online gas analyzer. It is reported for the first time that the presence of CuO could hinder the activity of Niâbased catalysts in H2 production, and experimental results show that the negative effect of CuO is strengthened with increasing CuO content and calcination temperature during sample preparation. With the help of a series of specific test and characterization techniques (SEMâEDS, BET, XRD, TPR and XPS), interaction rules between NiO and CuO was further investigated and understood, and based on that an action mechanism model was proposed. Furthermore, an arrangement of mixed particles that avoiding the intimate contact of CuO/NiO was suggested and tested, and a superior performance was demonstrated while observing no restrictions of CuO on Niâbased catalysts in sorptionâenhanced steamâmethane reforming under the conditions of CaâCu chemical looping
Dealloyed porous gold anchored by: In situ generated graphene sheets as high activity catalyst for methanol electro-oxidation reaction
A novel one-step method to prepare the nanocomposites of reduced graphene oxide (RGO)/nanoporous gold (NPG) is realized by chemically dealloying an Al2Au precursor. The RGO nanosheets anchored on the surface of NPG have a cicada wing like shape and act as both conductive agent and buffer layer to improve the catalytic ability of NPG for methanol electro-oxidation reaction (MOR). This improvement can also be ascribed to the microstructure change of NPG in dealloying with RGO. This work inspires a facile and economic method to prepare the NPG based catalyst for MOR
Flexible generation of structured terahertz fields via programmable exchange-biased spintronic emitters
Structured light, particularly in the terahertz frequency range, holds
considerable potential for a diverse range of applications. However, the
generation and control of structured terahertz radiation pose major challenges.
In this work, we demonstrate a novel programmable spintronic emitter that can
flexibly generate a variety of structured terahertz waves. This is achieved
through the precise and high-resolution programming of the magnetization
pattern on the emitter surface, utilizing laser-assisted local field cooling of
an exchange-biased ferromagnetic heterostructure. Moreover, we outline a
generic design strategy for realizing specific complex structured terahertz
fields in the far field. Our device successfully demonstrates the generation of
terahertz waves with diverse structured polarization states, including
spatially separated circular polarizations, azimuthal or radial polarization
states, and a full Poincare beam. This innovation opens a new avenue for
designing and generating structured terahertz radiations, with potential
applications in terahertz microscopy, communication, quantum information, and
light-matter interactions
Matching of kinetics of CaCO3 decomposition and CuO reduction with CH4 in Ca-Cu chemical looping
Ca-Cu chemical looping (CaL-CLC) based on calcium looping is a novel and promising process for CO capture. The concept utilizes the heat released from the exothermic reduction of CuO to support the endothermic regeneration of CaO-based sorbents. Therefore, it is important for the two major reactions to have matching kinetics. This work assesses kinetics of the two reactions in a calciner under the conditions of interest for CaL-CLC. The reaction rates of the decomposition of CaCO and reduction of CuO-based material with CH were measured in a TGA by varying the temperature and gas atmosphere, and two gas-solid reaction models were utilized for the determination of the kinetic parameters. On the basis of these results, a dynamic model was developed to investigate the simultaneous reduction of CuO and decomposition of CaCO in an adiabatic fixed-bed reactor operating at 1atm. The simulation results showed that the reduction of CuO completed extremely fast under all test conditions, and it could lead to hot spots in the calciner. It was found that addition of steam into the reducing gas could enhance the reaction rate of CaCO decomposition and help it match the fast rate of CuO reduction, then reduce the formation of hot spots. Also, steam could be used to control the movement of reaction front. Although CO could be used to control the reaction front as well, the higher CO partial pressure in CH was found to slow down the decomposition of CaCO leading to incomplete reaction
Macro-meso mechanical properties of gas hydrate bearing coal under triaxial compression with flexible boundary condition
To explore the influence of confining pressure on the macro-meso mechanical characteristics of gas hydrate bearing coal (GHBC) under different boundary conditions, the biaxial discrete element tests were carried out subjected to the confining pressures of 12ďź16 and 20 MPa for GHBC with saturation of 80%. Firstly, the biaxial numerical models of GHBC were established for flexible and rigid boundaries, using the linear model of the rolling resistance and the parallel bonding model. These numerical models incorporated the influences of particle shape effect, the hydrate cementation and the heat-shrinkable pipe. Then, the reliability of the numerical model was verified, by comparing with the indoor test results (stress-strain curves, bulk strain curves, internal friction angle cohesion and specimen failure modes). It is found that the flexible boundary can better reflect the deviatoric, stress-axial strain, the shear expansion and the strength characteristics of the sample. Based on the established numerical model, the roles of the confining pressure and the boundary condition on the macro-meso mechanical properties of GHBC were clarified from the perspectives of the internal displacement field, the mean mechanical coordination number, the mean porosity, the contact force chain and the hydrate bond failure. The results show that: â with the increase of confining pressure, the numerical sample with the rigid boundary mostly exhibits the single inclined plane shear failure, while that with the flexible boundary varies from the single fork shear failure to the single inclined plane shear failure. ⥠With the increase of confining pressure, for the two boundaries, the mean mechanical coordination numbers increase and the mean porosity decrease, leading to a denser and higher strength of the sample. ⢠With the increase of confining pressure, the normal contact force between particles continues to increase, and the sample strength increases. The normal contact force distributed near the axial direction increases, while that near the horizontal direction varies weakly. The higher the confining pressure is, the more difference between the vertical and the horizontal normal contact forces have, the more prominent the anisotropy is. The normal contact force increases by 54.50%, at the flexible boundary, and increases by 45.70%, at the peak strength point, with the confining pressure increasing from 12 MPa to 20 MPa. ⣠Under different confining pressures and boundary conditions, the samples fail with two different failure modes, tensile and shear. The samples mainly crack from the shear between the hydrate and coal. The research results reveal the mechanism of the influence of confining pressure on the strength deformation and failure of GHBC on the mesoscale
CERKL regulates autophagy via the NAD-dependent deacetylase SIRT1
<p>Macroautophagy/autophagy is an important intracellular mechanism for the maintenance of cellular homeostasis. Here we show that the <i>CERKL</i> (ceramide kinase like) gene, a retinal degeneration (RD) pathogenic gene, plays a critical role in regulating autophagy by stabilizing SIRT1. <i>In vitro</i> and <i>in vivo</i>, suppressing CERKL results in impaired autophagy. SIRT1 is one of the main regulators of acetylation/deacetylation in autophagy. In CERKL-depleted retinas and cells, SIRT1 is downregulated. ATG5 and ATG7, 2 essential components of autophagy, show a higher degree of acetylation in CERKL-depleted cells. Overexpression of SIRT1 rescues autophagy in CERKL-depleted cells, whereas CERKL loses its function of regulating autophagy in SIRT1-depleted cells, and overexpression of CERKL upregulates SIRT1. Finally, we show that CERKL directly interacts with SIRT1, and may regulate its phosphorylation at Ser27 to stabilize SIRT1. These results show that CERKL is an important regulator of autophagy and it plays this role by stabilizing the deacetylase SIRT1.</p
Application of different watershed units to debris flow susceptibility mapping: A case study of Northeast China
The main purpose of this study was to compare two types of watershed units divided by the hydrological analysis method (HWUs) and mean curvature method (CWUs) for debris flow susceptibility mapping (DFSM) in Northeast China. Firstly, a debris flow inventory map consisting of 129 debris flows and 129 non-debris flows was randomly divided into a ratio of 70% and 30% for training and testing. Secondly, 13 influencing factors were selected and the correlations between these factors and the debris flows were determined by frequency ration analysis. Then, two types of watershed units (HWUs and CWUs) were divided and logistic regression (LR), multilayer perceptron (MLP), classification and regression tree (CART) and Bayesian network (BN) were selected as the evaluation models. Finally, the predictive capabilities of the models were verified using the predictive accuracy (ACC), the Kappa coefficient and the area under the receiver operating characteristic curve (AUC). The mean AUC, ACC and Kappa of four models (LR, MLP, CART and BN) in the training stage were 0.977, 0.931, and 0.861, respectively, for the HWUs, while 0.961, 0.905, and 0.810, respectively, for the CWUs; in the testing stage, were 0.904, 0.818, and 0.635, respectively, for the HWUs, while 0.883, 0.800, and 0.601, respectively, for the CWUs, which showed that HWU model has a higher debris flow prediction performance compared with the CWU model. The CWU-based model can reflect the spatial distribution probability of debris flows in the study area overall and can be used as an alternative model
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A Novel Signal Transduction Pathway that Modulates <i>rhl</i> Quorum Sensing and Bacterial Virulence in <i>Pseudomonas aeruginosa</i>
The rhl quorum-sensing (QS) system plays critical roles in the pathogenesis of P. aeruginosa. However, the regulatory effects that occur directly upstream of the rhl QS system are poorly understood. Here, we show that deletion of gene encoding for the two-component sensor BfmS leads to the activation of its cognate response regulator BfmR, which in turn directly binds to the promoter and decreases the expression of the rhlR gene that encodes the QS regulator RhlR, causing the inhibition of the rhl QS system. In the absence of bfmS, the Acka-Pta pathway can modulate the regulatory activity of BfmR. In addition, BfmS tunes the expression of 202 genes that comprise 3.6% of the P. aeruginosa genome. We further demonstrate that deletion of bfmS causes substantially reduced virulence in lettuce leaf, reduced cytotoxicity, enhanced invasion, and reduced bacterial survival during acute mouse lung infection. Intriguingly, specific missense mutations, which occur naturally in the bfmS gene in P. aeruginosa cystic fibrosis (CF) isolates such as DK2 strains and RP73 strain, can produce BfmS variants (BfmSL181P, BfmSL181P/E376Q, and BfmSR393H) that no longer repress, but instead activate BfmR. As a result, BfmS variants, but not the wild-type BfmS, inhibit the rhl QS system. This study thus uncovers a previously unexplored signal transduction pathway, BfmS/BfmR/RhlR, for the regulation of rhl QS in P. aeruginosa. We propose that BfmRS TCS may have an important role in the regulation and evolution of P. aeruginosa virulence during chronic infection in CF lungs.</p
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