In order to understand the influence of brittleness and confining stress on rock cuttability, the indentation tests were carried out by a conical pick on the four types of rocks. Then, the ...experimental results were utilized to take regression analysis. The eight sets of normalized regression models were established for reflecting the relationships of peak indentation force (PIF) and specific energy (SE) with brittleness index and uniaxial confining stress. The regression analyses present that these regression models have good prediction performance. The regressive results indicate that brittleness indices and uniaxial confining stress conditions have non-linear effects on the rock cuttability that is determined by PIF and SE. Finally, the multilayer perceptual neural network was used to measure the importance weights of brittleness index and uniaxial confining stress upon the influence for rock cuttability. The results indicate that the uniaxial confining stress is more significant than brittleness index for influencing the rock cuttability.
The selective hydrogenation of CO
to value-added chemicals is attractive but still challenged by the high-performance catalyst. In this work, we report that gallium nitride (GaN) catalyzes the direct ...hydrogenation of CO
to dimethyl ether (DME) with a CO-free selectivity of about 80%. The activity of GaN for the hydrogenation of CO
is much higher than that for the hydrogenation of CO although the product distribution is very similar. The steady-state and transient experimental results, spectroscopic studies, and density functional theory calculations rigorously reveal that DME is produced as the primary product via the methyl and formate intermediates, which are formed over different planes of GaN with similar activation energies. This essentially differs from the traditional DME synthesis via the methanol intermediate over a hybrid catalyst. The present work offers a different catalyst capable of the direct hydrogenation of CO
to DME and thus enriches the chemistry for CO
transformations.
A series of true-triaxial compression tests were performed on red sandstone cubic specimens with a circular hole to investigate the influence of depth on induced spalling in tunnels. The failure ...process of the hole sidewalls was monitored and recorded in real-time by a micro-video monitoring equipment. The general failure evolution processes of the hole sidewall at different initial depths (500 m, 1000 m and 1500 m) during the adjustment of vertical stress were obtained. The results show that the hole sidewall all formed spalling before resulting in strain rockburst, and ultimately forming a V-shaped notch. The far-field principal stress for the initial failure of the tunnel shows a good positive linear correlation with the depth. As the depth increases, the stress required for the initial failure of the tunnels clearly increased, the spalling became more intense; the size and mass of the rock fragments and depth and width of the V-shaped notches increased, and the range of the failure zone extends along the hole sidewall from the local area to the entire area. Therefore, as the depth increases, the support area around the tunnel should be increased accordingly to prevent spalling.
Magnesium chelatase (MgCh) is a heterotrimeric enzyme complex, composed of two AAA+ family subunits that can assembly into a double ring structure and a large catalytic subunit. The small AAA+ ...subunit has ATPase activity and can self‐oligomerize into a ring structure, while the other AAA+ subunit lacks independent ATPase activity. Previous structural studies of the ATPase motor subunit of MgCh from a bacteriochlorophyll‐synthesizing bacterium have identified a unique ATPase clade, but the model of oligomeric assembly is unclear. Here we present the hexameric structure of the MgCh ATPase motor subunit from the chlorophyll‐synthesizing cyanobacterium Synechocystis sp. PCC 6803. This structure reveals details of how the hexameric ring is assembled, and thus provides a basis for further studying the heterotrimeric complex.
A considerable number of deep engineering cases show that strain rockbursts occur on both sidewalls of circular caverns and ultimately form a symmetrical V-shaped notch. To investigate the occurrence ...process and mechanism of strain rockbursts in deep circular cavern under high stresses, simulation experiments under four different three-dimensional (3D) stress conditions were conducted on cubic granite specimens with a prefabricated circular hole using the true-triaxial electro-hydraulic servo mutagenesis testing system. The rock bursting process was monitored on the sidewalls of the hole and recorded in real-time with a wireless microcamera. The results show that the entire rock bursting process on the sidewalls can be divided into four distinct periods for every 3D stress condition: calm period, pellet ejection period, rock fragment exfoliation period, and rock bursting period. Under the conditions that the vertical stress is constant and the horizontal radial stress is equal to the horizontal axial stress, the rockburst severity of the sidewalls clearly decreases with increasing horizontal stress. When the vertical stress is constant and the horizontal axial stress is low, the rockburst severity clearly decreases with the increase of horizontal radial stress. In contrast, when the horizontal axial stress is high, the rockburst severity becomes more serious with increasing horizontal radial stress. During the process of rock fracture and bursting, the damage zones on both sidewalls form two symmetrical V-shaped notches, and the line connecting the centres of the two V-shaped notches is perpendicular to the maximum principal stress direction. The symmetrical V-shaped failure modes on both sidewalls under the four stress conditions are in line with the statistical relationship of the far-field stress state and failure mode of a deep circular cavern without support (Martin et al. in Can Geotech J 36(1):136–151, 1999).
The effects of high strain rates and low confining pressures on the dynamic mechanical properties of sandstone were investigated experimentally with a modified triaxial split Hopkinson pressure bar ...(SHPB) system. For comparison, dynamic uniaxial compression tests of the sandstone were also conducted by using a conventional SHPB system. The confining pressures used in the dynamic triaxial compression tests are 5, 7.5, 10, 12.5 and 15 MPa, and the strain rate of these tests varied from approximately 40 s−1 to 160 s−1. The results show that the dynamic uniaxial and triaxial compressive strengths of the sandstone will linearly increase with the logarithm of the stain rate. Under approximately the same strain rate, the dynamic triaxial compressive strength will linearly increase with the confining pressure. Although the peak strain has no dependence on the confining pressure, it will generally increase with the strain rate. The secant modulus is independent of the strain rate and confining pressure. Three trend diagrams, which reflect the influences of strain rate or confining pressure on the dynamic mechanical properties of sandstone in the uniaxial and triaxial compression tests, are given, and the correlation between the failure modes of the sandstone specimens and the characteristics of the stress-strain curves is also analyzed.
Coastal populations are expanding globally, resulting in great anthropogenic impacts on the organic matter in estuaries and regional carbon cycles. However, the molecular-level characteristics of ...dissolved organic matter (DOM) within highly disturbed estuaries are still not well understood. Here, water samples collected during two seasons (wet and dry) from the subtropical Pearl River Estuary of China were analyzed using absorption and fluorescence spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to determine the spatiotemporal variations in the DOM characteristics. In the seaward direction, the abundances of chromophoric and fluorescent DOM decreased by greater percentages than the bulk dissolved organic carbon concentration. The spectroscopy and FT-ICR MS analyses collectively indicated seaward declines in the aromaticity of DOM and terrestrial DOM contributions from natural terrestrial markers and anthropogenic synthetic surfactants. In particular, the S content in DOM was much higher here than in previously reported estuaries, suggesting a strong anthropogenic impact on the estuarine DOM. Greater terrestrial and anthropogenic signatures in DOM were observed in the wet season than in the dry season. Importantly, this study implies that the terrestrial and anthropogenic contributions to DOM were strongly driven by season in the anthropogenically disturbed subtropical estuary.
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•DOM level and chemistry were studied in an anthropogenically disturbed estuary.•Disturbed estuarine DOM contained high abundances of S-containing formulas.•Chromophoric and fluorescent DOM decreased faster than non-chromophoric DOM seaward.•DOM aromaticity and terrestrial natural and anthropogenic markers decreased seaward.•Greater terrestrial contribution in estuarine DOM was found in the wet season.
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•Various amorphous silica-alumina composites were synthesized by hydrolytic method.•Amorphous silica-alumina composite was revealed an efficient solid acid for SRD.•A stable ...bifunctional catalyst with >99% DME conversion and H2 yield was obtained.•DME hydrolysis was revealed the rate-limiting step for two-step reactions of SRD.
In this work, we demonstrate that the amorphous silica-alumina composite (ASA) is an efficient solid acid for the steam reforming of dimethyl ether (SRD). Thus, a series of ASA with different Si/Al molar ratios was synthesized via the modified hydrolytic method by using Al(NO3)3·9H2O and/or NaAlO2 as Al precursor and tetraethoxysilane as Si precursor, respectively. Irrespective of the synthesis conditions, all of ASA composites were in an amorphous nature. However, both the acidity and the surface area were significantly affected by the synthesis conditions, the extent of which depends on the specific precursor and Si/Al molar ratios. The ASA physically mixed with a commercial Cu/ZnO/Al2O3 was investigated as a bifunctional catalyst for SRD under the conditions of P=0.1 MPa and gas hourly space velocity of 4000 h−1. Results indicate that both the conversion of dimethyl ether (DME) and the hydrogen yield were strongly dependent on the acidic property of ASA and the ASA to Cu/ZnO/Al2O3 ratios. Following the two-step consecutive mechanism of SRD, the catalytic results were well explained based on the acidic property of ASA, and the synergetic effect between the two catalytic functions was found to play a crucial role in determining the activity and stability of the bifunctional catalyst. Moreover, the DME hydrolysis was revealed to be the rate-limiting step for SRD reactions in the case of ASA as an acidic catalyst. By optimizing the synthesis conditions of ASA and the composition of the bifunctional catalyst, greater than 99% of DME conversion and hydrogen yield was achieved, and was kept for a time on stream of 66 h without an observable decrease. Thus, ASA is a very efficient solid acid for SRD.
Recently, tetraphenylethene, triphenylamine and other man-made core AIE luminescent materials (AIEgens) have attracted significant scientific interest. However, the design and synthesis of natural ...product based, facile and color tunable AIEgens remains challenging. Herein, a novel series of AIEgens based on purine-core molecular rotors is reported, which can be facilely synthesized and shows color tunable emission. Moreover, these purine-based AIEgens exhibit lipid droplet specific properties in live cellular imaging with low background, high selectivity and excellent biocompatibility.
Conventional triaxial compression and “reducing confining pressure” experiments were carried out for red sandstone by an MTS815 Flex Test GT rock mechanics experimental system. Our results show that ...the post-peak axial deformation characteristics of red sandstone changed as the confining pressure was increased from 5 to 65 MPa. Young’s modulus of red sandstone increased nonlinearly with increasing confining pressure, but Poisson’s ratio remained unaffected. Using our new data, the compactive and dilatant behavior, strength and failure characteristics of sandstone under triaxial compression are further discussed. For our data, the nonlinear Hoek-Brown criterion better reflects the peak strength properties than the linear Mohr-Coulomb criterion. However, the residual strength shows a clear linear relationship with confining pressure, which can be best described using the linear Mohr-Coulomb criterion. The peak and residual strengths were not directly related to the two different loading paths. The onset of dilatancy (
C
′), the switch from compaction-dominated to dilatant-dominated behavior (
D
′) and the stress at zero volumetric strain all increased linearly with the confining pressure. In our conventional triaxial compression experiments, the failure mode changed from mixed tension and shear fracture (single shear fracture) to shear fracture with double slippage planes with increasing confining pressure. However, the failure mode in our “reducing confining pressure” experiments was more complicated and results mainly from the unstable failure characteristics of the rock during the reduction in confining pressure. Finally, based on our acoustic emission (AE) locations, at a confining pressure of 35 MPa, a detailed analysis of the evolutionary process of internal cracks is presented for the entire loading process.
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