Kagome lattice composed of transition-metal ions provides a great opportunity to explore the intertwining between geometry, electronic orders and band topology. The discovery of multiple competing ...orders that connect intimately with the underlying topological band structure in nonmagnetic kagome metals AV
Sb
(A = K, Rb, Cs) further pushes this topic to the quantum frontier. Here we report a new class of vanadium-based compounds with kagome bilayers, namely AV
Sb
(A = K, Rb, Cs) and V
Sb
, which, together with AV
Sb
, compose a series of kagome compounds with a generic chemical formula (A
Sb
)(V
Sb)
(m = 1, 2; n = 1, 2). Theoretical calculations combined with angle-resolved photoemission measurements reveal that these compounds feature Dirac nodal lines in close vicinity to the Fermi level. Pressure-induced superconductivity in AV
Sb
further suggests promising emergent phenomena in these materials. The establishment of a new family of layered kagome materials paves the way for designer of fascinating kagome systems with diverse topological nontrivialities and collective ground states.
Underground reservoir technology for coal mines can realize the coordinated development of coal exploitation and water protection in water-shortage-prone areas. The seepage effect of the floor ...seriously affects the safety of underground reservoirs under the action of mining damage and seepage pressure. Focusing on the problem of floor seepage in underground reservoirs, a spatial mechanical model of underground reservoirs was established. The main factors affecting the seepage of the surrounding rock were studied. The seepage pressure law in different stages of spatial structure evolution of overlying strata was explored. The results showed that pressure change was the main factor affecting the stability of a reservoir's surrounding rock. The pore space between the broken and fractured rock in the water-flowing fractured zone was the main water storage space, which was directly related to the development of a breaking arch. According to the spatial structure evolution process of the overlying strata, the water storage state of an underground reservoir was divided into two stages and three situations. The seepage pressure was mainly affected by the water pressure and the overlying strata weight. The water pressure was affected by the reservoir head height, and the overlying strata weight was mainly affected by the overlying strata thickness.
In the present work, we developed a micellar system of milk protein-surfactant (SDS)-graphene to prepare the graphene-based aerogels via hydrothermal and freeze-drying method, in which the novel ...surface-property of aerogels can be tuned with the decreasing of micellar size in the colloid systems resulting the improved specific surface area. The milk protein also severed as green and sustainable sources to introduce nitrogen heteroatoms into the aerogels. Subsequently, the aerogels were further graphitized and activated to fabricate N-doped porous nanocarbon at 600 °C. The initial surface composition and structure of the aerogel, which was proved, has obvious impact on the final structure of the synthesized nanocarbon materials, and thus influence their electrochemical activity. The optimized nanocarbon materials (MGPC-5), with enhanced specific surface area, degree of graphitization, and nitrogen doping, exhibited excellent capacitance performance and stability in both three-electrode system (518.8 F/g at a current density of 0.1 A/g) and symmetrical electrode system (120.8 F/g at current density of 0.1 A/g and with ~95% capacitance retention after 5000 cycles of charging and discharging at 3 A/g) in KOH. The assembled supercapacitor also shows ideal capacitive properties in series and parallel configurations. Tested with a stable 1.6 V windows in Li2SO4 electrolyte, the symmetric supercapacitor cell exhibits a high energy density up to 36.7 W h/kg. The present work provides a feasible fabrication method for high-performance supercapacitor based on graphene and biomass derived carbon, the proposed surface-property regulation and supercapacitor performance improvement strategy may also shed light on other energy related materials or system.
Milk micelles serve as multifunctional biomass additives to compose with graphene oxide for fabrication of nitrogen doped porous nanocarbon materials. The supramolecular interactions between the two components provide effective ability in regulation of the surface and porous property and improvement of the supercapacitor performance of nanocarbons. Display omitted
We performed a systematic investigation of the effective stress behaviors for permeability and deformation in relation to bedding anisotropy of two clayey sandstones. Permeability and deformation ...were measured in samples cored parallel and perpendicular to bedding over a broad range of hydrostatic pressures, covering ‘stage I’ for microcrack closure and ‘stage II’ for pore deformation. Our data show that bedding anisotropy has a significant influence on the effective stress coefficient for permeability, but little effect on the effective stress coefficient for pore volume change. The effective stress coefficient
κ
⊥
of permeability for flow perpendicular to bedding was consistently larger than the corresponding
κ
|
|
for parallel flow. The effective stress coefficient
β
|
|
for pore volume changes parallel to bedding and corresponding coefficient
β
⊥
values perpendicular to bedding coincided, because the scalar change of pore volume was not sensitive to the orientation of the samples. Furthermore, we confirmed that with the closure of preexisting microcracks, the effective stress coefficients for permeability in stages II were typically larger than the corresponding coefficients in stage I, and that the effective stress coefficients for axial strain and pore volume change decreased for samples both perpendicular and parallel to bedding. Our new results quantified the effect of bedding anisotropy and crack closure on the effective stress behavior of clayey sandstones.
Abstract
Unconventional quantum states, most notably the two-dimensional (2D) superconductivity, have been realized at the interfaces of oxide heterostructures where they can be effectively tuned by ...the gate voltage (
V
G
). Here we report that the interface between high-quality EuO (111) thin film and KTaO
3
(KTO) (110) substrate shows superconductivity with onset transition temperature
$$T_{{{\mathrm{c}}}^{{{\mathrm{onset}}}$$
T
c
onset
= 1.35 K. The 2D nature of superconductivity is verified by the large anisotropy of the upper critical field and the characteristics of a Berezinskii–Kosterlitz-Thouless transition. By applying
V
G
,
$$T_{{{\mathrm{c}}}^{{{\mathrm{onset}}}$$
T
c
onset
can be tuned from ~1 to 1.7 K; such an enhancement can be possibly associated with a boosted spin-orbit energy
$$\varepsilon _{{{\mathrm{so}}} = \hbar /\tau _{{{\mathrm{so}}}$$
ε
so
=
ħ
/
τ
so
, where
τ
so
is the spin-orbit relaxation time. Further analysis of
τ
so
based on the upper critical field (
H
c2
) and magnetoconductance reveals complex nature of spin-orbit coupling (SOC) at the EuO/KTO(110) interface with different mechanisms dominating the influence of SOC effects on the superconductivity and the magnetotransport in the normal state. Our results demonstrate that the SOC should be considered an important factor in determining the 2D superconductivity at oxide interfaces.
It is difficult to change the pattern of coal energy consumption in China over a short time frame. The combined action of static load (nonuniform load) and dynamic load (disturbance stress) often ...induces dynamic instability in underground engineering rock masses. It is difficult to quantitatively study the nonuniform load and disturbance stress of different underground projects by means of field monitoring. It is of great practical significance to study the failure characteristics of rock under the action of nonuniform and disturbance stresses and improve the understanding of engineering disaster prevention and control using laboratory tests. In view of the mechanical response mechanism of coal and rock masses under mining stress and the failure characteristics and disaster-causing mechanism of engineering rock masses under different disturbance forms, a research group studying mining dynamics independently developed a series of testing systems, including a “mining dynamic stress test system” and a “creep and dynamic disturbance impact loading test system”, which established a mining stress laboratory and used physical experiments to assess the above problems. Based on a series of test equipment and acoustic emission (AE) technology, with event location as the parameter index, the failure laws of rock strength and AE characteristics of samples with different horizontal stresses under nonuniform loading based on AE events and different disturbance stress loading paths are studied. The failure characteristics and time–space damage laws of rock under different disturbance combinations are restored at the test scale, and the time–space characteristics of rock damage and failure under nonuniform loading are revealed.Article HighlightsRelying on the self-developed “creep and dynamic disturbance impact loading test system”, the failure characteristics of engineering rock mass under disturbance stress was studied.Relying on the self-developed “Mining-induced stress test system”, the research on the temporal and spatial characteristics of damage and failure of engineering rock mass under non-uniform load was realized.The laboratory of mining stress was established,and the development process of mining stress was reproduced in the laboratory. Relevant achievements fill in the deficiency of mining dynamics test equipment.
Highwall mining, which is referred to the technique of extracting coal from the bottom of an exposed highwall, features safety, efficiency, and economy. According to existing highwall mining methods, ...the mining sequence has a great influence on highwall stability. Based on a highwall mining project in Australia, this study adopted the FLAC3D numerical simulation method to investigate the stability of coal pillars with different mining sequences. The results show that different mining sequences of boreholes exert a great effect on highwall stability. Compared with sequential mining, the skip mining method achieves higher speed of highwall stabilization and smaller plastic zone of coal pillar with its maximum strength decreasing by 12%. By adjusting the mining sequence scientifically, the coal pillar failure and roof collapse caused by the deviation of mining angle can be avoided. The results may provide a new angle for the studies on the coal pillar layout and stability design in highwall mining.
Design and experimental results of a continuous wave (CW), 94 GHz second harmonic gyrotron with a 1.8 T continuous operation solenoid are presented. In order to reduce power consumption of the ...solenoid, a carbon steel shell was designed to concentrate the magnetic flux into the gyrotron cavity region. The inner hole is 66 mm in diameter. That is big enough to insert a CW, medium power gyrotron. When driven by a current of 476 A, maximum magnetic field of 1.8 T in the cavity region was detected and the power consumption was 25 kW. The solenoid was cooled effectively with a water flow of 1.5 L/s. Based on the 1.8 T solenoid, a compact triode magnetron injection gun (MIG) was used to generate gyrating electron beam for the second harmonic gyrotron. The gyrotron operated at the TE
0,2
mode with a conventional cylindrical cavity. And a high-efficiency quasi-optical mode converter with a dimpled-wall launcher was designed, the mode conversion efficiency was 97%, and the Gaussian content of the output beam was 98%. During the CW test, continuous operation of 5 min was realized. Its operational frequency stabilized at 93.9 GHz. The output power was 12 kW with an electron beam of 45 kV, 1.6 A. The output efficiency was 24% with a single-stage depressed collector.
The evaluation of the risk is the prerequisite for the implementation of countermeasures in the prevention and control of rock burst, and the research on the fast forecast at scene of the rock burst ...is more important for the safety production of coal mine. Aiming at the problem that dynamic disasters caused by many factors and heterogeneity of coal and rock are difficult to predict in the process of coal mining, in this paper, the general law and the risk control factors of the rock burst are studied, a mathematical model based on the BP neural network was built according to the different actual mining conditions in the mining area, and the output layer has obtained the prediction result. Then, the results of the output samples after training were fitted by using SPSS software, and the fitting function was obtained by multiple least square fitting. Finally, the fitting results are checked by the data of actual coal mine dynamic disaster parameters. The prediction results show that the simulation results of BP neural network prediction model and the fitting function of the least square method can reduce the impact of subjective judgment on the prediction results, and the application of the fitting function can obtain the prediction results in the first time to ensure the construction safety. The method of on-site hazard assessment and inspection by using fitting function is simple and feasible and has high accuracy, which provides a new idea for the field prediction of rock burst.
To solve the problems of the rapid advance of the working face was delayed by complicated working procedure and high labor intensity, and the severe damage of roof bolt (anchor cable) induced by ...advanced hydraulic support, the deformation characteristics of surrounding rock, and the supporting principle of grouting truss anchor cable were analyzed theoretically by taking the roadway of 3_(down) coal seams 2326# working face in Sanhekou coal mine as the research object; then, the mechanical model of supporting structure of roadway under goaf was established. Based on this model, the optimal supporting scheme was determined, and the active advanced support technology scheme of “advanced grouting truss anchor cable” was proposed to take the place of the existing single pillar. The deformation and failure characteristics of surrounding rock of the working face leading roadway were observed and analyzed on-site. Within the allowable range of reading error, the results showed that the maximum displacement of medium-deep base point and shallow base point of two roadways was 15.2 cm and 10.9 cm, respectively; the pressure value had a more obvious jump increase when the distance between each measuring point and the working face was about 35 m, which means the range is strongly affected by the advance mining, and the area affected by advanced mining was 35 m ahead of the working face. It was observed that the lowest position of roof separation development ranged from 0.71 m to 2.73 m. The separation layer was generally distributed in the range of 0.73 m-2.49 m, and the fracture area was roughly distributed in the range of 0.01 m-0.62 m. Under the condition of overlying goaf, there was a complete stress structure, which can meet the requirements of suspension support.
PDF
