This study investigates the flexural behavior of UHPC materials containing steel fibers of varying lengths. Mesomechanical analysis is performed according to the analytical pullout model, using ...actual measured fiber distributions. The flexural behavior of UHPC after cracking is simulated by superposing the fiber bridging and matrix softening curves. Subsequently, the evolution of stress–strain along the axial crack of UHPC is evaluated under different loading conditions. The obtained results indicate that longer steel fibers can efficiently improve the flexural behavior of UHPC. Moreover, the actual fiber orientation and pullout length distributions can be well fitted by two-parameter probability distribution (PDF) and Gaussian functions, respectively. Based on the micromechanical analysis, the fiber bridging behavior is overestimated under the assumption of 2D random fiber distribution, and it is underestimated under the assumption of 3D random fiber distribution. Interestingly, the length of the shear lag zone is independent of the fiber length, which is about 20.16 mm. The obtained results demonstrate that the compressive stress and strain at the top of the tested specimen gradually transform into tensile stress and strain at the opposite side. Interestingly, the stress of the specimens with fiber length of 20 mm are slightly higher than the specimens with fiber lengths of 6 and 13 mm, and the strain just lower than the specimens with fiber lengths of 6 and 13 mm in all crack propagation stages, respectively. This indicates that, in addition to the number of steel fibers, the stress/strain dispersion depends on fiber length.
Fatigue crack propagation behavior in ultra-high-performance concrete (UHPC) containing different volume fractions of steel fibers is investigated under cyclic flexural loading at various stress ...levels. Evolutions of the crack mouth opening displacement, crack tip strain, and crack propagation length are characterized during continuous loading cycles via digital image correlation. Test data are fit to smooth, continuous logarithmic functions to discern relationships between evolving crack length and the number of loading cycles. The crack propagation rates of different UHPC specimens are then determined from the first derivative of these logarithmic functions. A critical crack length of approximately 20 mm is found in UHPC containing a fiber volume fraction (Vf) of 0.5%, while that of other specimens (Vf = 1.0%, 1.5%, and 2.0%) is found to approach 60 mm under the stress levels of 0.80, 0.75, 0.70 and 0.65. Strain diagrams obtained via DIC reveal no obvious changes for the crack growth along the y-direction in UHPC specimens containing fiber volume fractions of 0.5% and 1.0%, while a tendency for strain concentrations oriented at 45° characterizes crack development in specimens containing 1.5% and 2.0% volume fractions of fiber. Crack propagation rates during the stable stage of crack propagation decrease upon reducing applied stress level and with increased content of steel fiber reinforcement, providing predominant means to enhance fatigue life.
Compared with the surface, the deep environment has the advantages of allowing “super-quiet and ultra-clean”-geophysical field observation with low vibration noise and little electromagnetic ...interference, which are conducive to therealization of long-term and high-precision observation of multi-physical fields, thus enabling the solution of a series of geoscience problems. In the Panyidong Coal Mine, where there are extensive underground tunnels at the depth of 848 m belowsea level, we carried out the first deep-underground geophysical observations, including radioactivity, gravity, magnetic, magne-totelluric, background vibration and six-component seismic observations. We concluded from these measurements that (1) the background of deep subsurface gravity noise in the long-period frequency band less than 2 Hz is nearly two orders ofmagnitude weaker than that in the surface observation environment; (2) the underground electric field is obviously weaker thanthe surface electric field, and the relatively high frequency of the underground field, greater than 1 Hz, is more than two orders of magnitude weaker than that of the surface electric field; the east-west magnetic field underground is approximately the same asthat at the surface; the relatively high-frequency north-south magnetic field underground, below 10 Hz, is at least one order ofmagnitude lower than that at the surface, showing that the underground has a clean electromagnetic environment; (3) in additionto the high-frequency and single-frequency noises introduced by underground human activities, the deep underground spacehas a sig-nificantly lower background vibration noise than the surface, which is very beneficial to the detection of weakearthquake and gravity signals; and (4) the underground roadway support system built with ferromagnetic material interferesthe geomagnetic field. We also found that for deep observation in the “ultra-quiet and ultra-clean” environment, the existinggeophysical equipment and observation technology have problems of poor adaptability and insufficient precision as well asdata cleaning problems, such as the effective separation of the signal and noise of deep observation data. It is also urgent tointerpret and comprehensively utilize these high-precision multi-physics observation data.
Tianchi tunnel from construction to now has occurred 9 serious water inrush (gushing) accidents, resulting in a large number of economic, social and ecological damage to the environment. This paper ...carried out thorough theoretical analysis and field observation from Tianchi tunnel stratum rock properties, engineering geology, hydrogeology, the surrounding patch, runoff and drainage and the changes of surface water environment, as well as tunnel excavating. The reasons that had obtained from the previous 9 water inrush (gushing) of Tianchi tunnel. Some effective references had put forward for the engineering treatment, provided some valuable references for other similar underground engineering construction.
Na-ion batteries have been considered promising candidates for stationary energy storage. However, their wide application is hindered by issues such as high cost and insufficient electrochemical ...performance, particularly for cathode materials. Here, we report a solvent-free mechanochemical protocol for the in-situ fabrication of sodium vanadium fluorophosphates. Benefiting from the nano-crystallization features and extra Na-storage sites achieved in the synthesis process, the as-prepared carbon-coated Na
(VOPO
)
F nanocomposite exhibits capacity of 142 mAh g
at 0.1C, higher than its theoretical capacity (130 mAh g
). Moreover, a scaled synthesis with 2 kg of product was conducted and 26650-prototype cells were demonstrated to proof the electrochemical performance. We expect our findings to mark an important step in the industrial application of sodium vanadium fluorophosphates for Na-ion batteries.
Display omitted
•Two flavonoids were discovered as characteristic markers for Am monofloral honey.•A combined untargeted and targeted MS method was used for marker identification.•Calycosin exerted ...excellent antioxidant activity in free radical scavenging assays.
Astragalus membranaceus var. mongholicus Hsiao (Am) is a widely used traditional Chinese herbal medicine. The monofloral honey from Am plant nectar collected by honeybees (MH-Am) has potential medicinal activities. Quality control of MH-Am requires discovery of characteristic markers. In this study, calycosin and formononetin were identified as reliable chemical markers for MH-Am authentication, which were shared with its plant (P-Am), but absent in other honeys based on untargeted mass spectrometry (MS) analysis. The contents of calycosin and formononetin in MH-Am, other honeys and P-Am were determined through a targeted MS-based quantitative approach. Furthermore, free radical scavenging assays showed that calycosin functioned directly in the antioxidative activity of MH-Am. Thus, calycosin has great potential to be certified as a bioactive marker contributing to future quality control of commercial MH-Am products.
SBA-15 mesoporous materials functionalized with 2-acetylthiophene-derived Schiff's base denoted as A-SBA-15, were synthesized for removal of Cr(III) ions from aqueous solution. The adsorbent ...materials were characterized by means of XRD, SEM, TEM, N2 adsorption-desorption, TGA, EDXS, FTIR, 13C CP-MAS NMR and XPS. Tests were then performed to investigate the adsorption of Cr(III) ions onto A-SBA-15 in batch systems. The maximum adsorption capacity of A-SBA-15 (114.2 mg/g) for Cr(III) ions was much higher than that of the pure SBA-15 (15.6 mg/g). The kinetics analysis revealed that the adsorption process was well described by pseudo-second-order kinetic model. In addition, the Langmuir isotherm model was better fitted with the adsorption data for Cr(III) compared to the Freundlich isotherm model. Furthermore, the Cr(III) adsorption onto A-SBA-15 was found to be spontaneous, endothermic, and mainly chemical adsorption as shown by the investigate of various thermodynamic parameters, such as, ΔG°, ΔH°, and ΔS°. The characterization of A-SBA-15 materials before and after adsorption of Cr(III) ions showed that the chemical combination of the organic groups on A-SBA-15 and Cr(III) ions through coordination bond. The as-prepared A-SBA-15 materials could be reused in five successive recycles without significantly decreasing its adsorption capacity. Moreover, four batches of A-SBA-15 prepared at different synthesis times have the similar adsorption capacity. Besides, the adsorbent showed good selective separation of Cr(III) ion in the presence of Cu(II), Zn(II) and Ni(II) ions. The good reproductivity, reusability and selectivity suggest that A-SBA-15 material can be used as a promising adsorbent for efficient removal of heavy metals from aqueous solution.
Display omitted
•A novel adsorbent A-SBA-15 material was prepared by Schiffs' base reaction.•The A-SBA-15 materials have potential applications for efficient removal of Cr(III) ions.•The A-SBA-15 materials process excellent adsorption properties toward Cr(III) ions.•The A-SBA-15 material has good reproducibility, reusability and adsorption selectivity.
Display omitted
•Our results show that the doped N enhanced the adsorption and charge of Pd, which can lead to higher catalytic activity.•The doped N can also enhance the adsorption of H and make it ...more difficult to migrate on graphene.•It is speculated that one migration path of H on the N-doped graphene through the Pd atom.
Using first-principles calculations, the rule of N in N-doped graphene supported Pd catalyst was investigated. Our results show that the doped N enhanced the adsorption and charge of Pd, which can lead to higher catalytic activity. Meanwhile, the doped N can also enhance the adsorption of H and make it more difficult to migrate on graphene. But the doped N is conductive to overflow of H from the Pd to graphene, the energy barrier is reduced from 1.01 eV to 0.85 eV. Therefore, it is speculated that one migration path of H on the N-doped graphene through the Pd atom.
Cortical GABAergic inhibitory interneurons have crucial roles in the development and function of the cerebral cortex. In rodents, nearly all neocortical interneurons are generated from the ...subcortical ganglionic eminences. In humans and nonhuman primates, however, the developmental origin of neocortical GABAergic interneurons remains unclear. Here we show that the expression patterns of several key transcription factors in the developing primate telencephalon are very similar to those in rodents, delineating the three main subcortical progenitor domains (the medial, lateral and caudal ganglionic eminences) and the interneurons tangentially migrating from them. On the basis of the continuity of Sox6, COUP-TFII and Sp8 transcription factor expression and evidence from cell migration and cell fate analyses, we propose that the majority of primate neocortical GABAergic interneurons originate from ganglionic eminences of the ventral telencephalon. Our findings reveal that the mammalian neocortex shares basic rules for interneuron development, substantially reshaping our understanding of the origin and classification of primate neocortical interneurons.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Display omitted
•Enhanced catalytic activity of Fe-Mo, Fe-Ni and Fe-Pt bimetallic Fe catalysts for ammonia decomposition is theoretically assessed.•The electronic effects of the do-pant atoms are ...elucidated.•An inverse correlation is analyzed between the N adsorption and the catalyst.
Usually alloy catalysts can achieve superior performance, it is found by DFT that the Fe-Mo, Fe-Ni and Fe-Pt bimetallic catalysts can all enhance catalytic activity of Fe-based catalysts for ammonia decomposition. Compared to the step of the cleavage of NH2-H bond, the step of N + N recombination remains a rate-controlling step for these bimetallic catalysts, and the energy barriers of which are reduced from 2.86 eV to 2.57 eV, 2.28 eV and 1.75 eV, respectively. Moreover, within the scope of our study, there is an inverse correlation between the N adsorption and the catalyst activity.
PDF
