In multiple-seam mining, severe deformation of roadways and coal bursts caused by overlying coal pillars can occur in the lower seams. Overburden movement and ground pressure behaviour when mining ...thick seam below the strong roof and upper four extracted coal seams were investigated in the Tongxin coal mine, China. The numerical model indicated that the abutment stress in the lower seam is affected by overlying coal pillars as suggested by the bubble and the cantilever beam models. The microseismic monitoring indicated that high-energy seismic events caused by large overburden movement under the overlying pillars were the source of the dynamic loads. The influence of upper pillar on lower longwall mining conditions can be broken down into three cases: (a) under no pillar area, no excessive deformation or dynamic failure was observed in the tailgate with medium static loads and low dynamic loads; (b) under single pillars or two overlapping pillars, severe deformation occurred in the tailgate with low to medium static loads and medium dynamic loads; and (c) under the three to four overlapping pillars, extreme deformation was observed with the high static loads and high dynamic loads. These findings can provide guidance for the roadway layout in the multiple-seam operations.
3D printed deformable sensors Zhu, Zhijie; Park, Hyun Soo; McAlpine, Michael C
Science advances,
06/2020, Letnik:
6, Številka:
25
Journal Article
Recenzirano
Odprti dostop
The ability to directly print compliant biomedical devices on live human organs could benefit patient monitoring and wound treatment, which requires the 3D printer to adapt to the various ...deformations of the biological surface. We developed an in situ 3D printing system that estimates the motion and deformation of the target surface to adapt the toolpath in real time. With this printing system, a hydrogel-based sensor was printed on a porcine lung under respiration-induced deformation. The sensor was compliant to the tissue surface and provided continuous spatial mapping of deformation via electrical impedance tomography. This adaptive 3D printing approach may enhance robot-assisted medical treatments with additive manufacturing capabilities, enabling autonomous and direct printing of wearable electronics and biological materials on and inside the human body.
Coal burst has become a worldwide problem that needs to be solved urgently for the sake of coal mine safety production due to its complicated triggering mechanisms and numerous influencing factors. ...The risk assessment of coal burst disasters is particularly critical. In this work, 15 factors affecting coal burst occurrence are selected from the perspectives of geodynamic environment and geological and mining conditions, and the influence mechanism of each factor on coal bursts is analyzed. An evaluation index system of coal burst risk is put forward. A hierarchical model of coal burst prediction is established, and the weight of each influencing factor to coal burst risk is calculated. Based on the fuzzy comprehensive evaluation method, a coal burst prediction model is established, which can scientifically decompose and simplify the complicated problem and make coal burst prediction and prevention more pertinent and effective. The model is applied to assess the coal burst risk level of a coal mine in Shanxi Province, and the evaluation result is consistent with practical situations. This method considers the influencing factors comprehensively and determines the weight of each factor scientifically compared with other forecasting methods.
Conventional 3D printing technologies typically rely on open‐loop, calibrate‐then‐print operation procedures. An alternative approach is adaptive 3D printing, which is a closed‐loop method that ...combines real‐time feedback control and direct ink writing of functional materials in order to fabricate devices on moving freeform surfaces. Here, it is demonstrated that the changes of states in the 3D printing workspace in terms of the geometries and motions of target surfaces can be perceived by an integrated robotic system aided by computer vision. A hybrid fabrication procedure combining 3D printing of electrical connects with automatic pick‐and‐placing of surface‐mounted electronic components yields functional electronic devices on a free‐moving human hand. Using this same approach, cell‐laden hydrogels are also printed on live mice, creating a model for future studies of wound‐healing diseases. This adaptive 3D printing method may lead to new forms of smart manufacturing technologies for directly printed wearable devices on the body and for advanced medical treatments.
An adaptive 3D printing system capable of printing functional conductive inks and bioinks on moving freeform surfaces yields wireless electronics on a moving human hand and cell‐laden biostructures on mice. The concept of printing functional and biological materials via an autonomous, adaptive 3D printing system suggests a new paradigm for printing on‐the‐fly wearable electronics on moving targets and for surgical applications.
Photonic crystals (PCs) have been widely applied in optical, energy, and biological fields owing to their periodic crystal structure. However, the major challenges are easy cracking and poor ...structural color, seriously hindering their practical applications. Now, hydrophobic poly(tert‐butyl acrylate) (P(t‐BA)) PCs have been developed with relatively lower glass transition temperature (Tg), large crack‐free area, excellent hydrophobic properties, and brilliant structure color. This method based on hydrophobic groups (tertiary butyl groups) provides a reference for designing new kinds of PCs via the monomers with relatively lower Tg. Moreover, the P(t‐BA) PCs film were applied as the photoluminescence (PL) enhanced film to enhance the PL intensity of CdSe@ZnS QDs by 10‐fold in a liquid‐crystal display (LCD) device. The new‐type hydrophobic force assembled PCs may open an innovative avenue toward new‐generation energy‐saving devices.
A tert‐butyl acrylate (t‐BA) monomer for the construction of hydrophobic P(t‐BA) photonic crystals toward magnetic‐optics displays and energy saving devices is presented. It may open an innovative avenue toward the assembled PC field.
The efficiency of heterogeneous photocatalysis for converting solar to chemical energy is low on a per photon basis mainly because of the difficulty of capturing and utilizing light across the entire ...solar spectral wavelength range. This challenge is addressed herein with a plasmonic superstructure, fashioned as an array of nanoscale needles comprising cobalt nanocrystals assembled within a sheath of porous silica grown on a fluorine tin oxide substrate. This plasmonic superstructure can strongly absorb sunlight through different mechanisms including enhanced plasmonic excitation by the hybridization of Co nanoparticles in close proximity, as well as inter‐ and intra‐band transitions. With nearly 100% sunlight harvesting ability, it drives the photothermal hydrogenation of carbon dioxide with a 20‐fold rate increase from the silica‐supported cobalt catalyst. The present work bridges the gap between strong light‐absorbing plasmonic superstructures with photothermal CO2 catalysis toward the complete utilization of the solar energy.
A cobalt plasmonic superstructure is developed to enable almost 100% broadband photon efficient CO2 photocatalysis through enhanced plasmonic excitation by the hybridization of Co nanoparticles in close proximity, as well as inter‐ and intra‐band transitions. This work will bridge the gap between plasmonic absorbers with photothermal catalysis, toward the complete utilization of the solar energy.
Coal burst proneness of coal mass is a leading factor of coal burst which is influenced by fissures. In this paper, the elastic strain energy (ESE) and residual energy index (REI) were used as coal ...burst proneness indicators. The calibrated PFC2D models of coal specimens with various fissure configurations were established, and uniaxial compression tests were conducted. It was found that the uniaxial compressive strength (UCS), ESE, and REI for three types of fissured coal specimen were similar. The aforementioned three parameters decrease as the inclination angle increases from 0° to 30°. On the other hand, these parameters increase as the inclination angle increases from 30° to 90°. Through the coal burst proneness comparison of various fissure configurations, it was found that the coal burst proneness in the condition of two coplanar-parallel fissures was greater than that in the condition of a single fissure, whereas the coal burst proneness in the condition of two non-coplanar-parallel fissures was the lowest. The crack initiation stress, crack initiation stress level, and elastic strain energy distribution could explain the influence mechanism of fissures on the coal burst proneness. These results can be used as a guideline for forecasting and preventing coal burst.
The hard roof of coal mines has the characteristics of high hardness, good integrity, and large layer thickness, which leads to many ground control problems. To reveal the influence of a hard roof ...structure on the stress performance and coal pillar stability during mining operations, the 8,104 and 8,105 working faces in the Tongxin coal mine were considered as the research object to analyze the stress behavior during the working face advance. Numerical simulation software FLAC
3D
was used to establish the numerical model of the longwall face under hard roof conditions. The stress distribution laws and coal pillar stability under different roof strengths were analyzed so as to explain the impacts of the hard roof on the stress distribution at the working face. The results show that during the second face proceeding, the influence zone of the front abutment pressure under hard roof conditions is 6 m wider than that under soft roof conditions, and the bearing stress at the working face is 10.4 MPa higher. At the mining position, the plastic zone of the pillar under hard roof conditions is 11 m wider than that under soft roof conditions, and the peak vertical stress is 5.13 MPa higher than that under soft roof conditions. At 25 m ahead of the working face, the plastic zone of the pillar under hard roof conditions is 6 m wider than that under soft roof conditions, and the peak vertical stress is 24.84 MPa higher than that under soft roof conditions. Additional overburden pressure produced by the uncaved hard roof increased pillar stress and plastic zones. Therefore, the hard roof is the main cause of strong ground pressure behavior in the Tongxin coal mine. Aiming at the strong mine pressure behavior, it is suggested to adopt the pre-splitting technology to reduce the influence of the hard roof on mine pressure.
Development of fast curing and easy modeling of colloidal photonic crystals is highly desirable for various applications. Here, a novel type of injectable photonic hydrogel (IPH) is proposed to ...achieve self‐healable structural color by integrating microfluidics‐derived photonic supraballs with supramolecular hydrogels. The supramolecular hydrogel is engineered via incorporating β‐cyclodextrin/poly(2‐hydroxypropyl acrylate‐co‐N‐vinylimidazole) (CD/poly(HPA‐co‐VI)) with methacrylated gelatin (GelMA), and serves as a scaffold for colloidal crystal arrays. The photonic supraballs derived from the microfluidics techniques, exhibit excellent compatibility with the hydrogel scaffolds, leading to enhanced assembly efficiency. By virtue of hydrogen bonds and host–guest interactions, a series of self‐healable photonic hydrogels (linear, planar, and spiral assemblies) can be facilely assembled. It is demonstrated that the spherical symmetry of the photonic supraballs endows them with identical optical responses independent of viewing angles. In addition, by taking the advantage of angle independent spectrum characteristics, the IPH presents beneficial effects in reflective cooling, which can achieve up to 17.4 °C in passive solar reflective cooling. The strategy represents an easy‐to‐perform platform for the construction of IPH, providing novel insights into macroscopic self‐assembly toward thermal management applications.
An injectable photonic hydrogel is proposed to achieve self‐healable structural color for facile curing of colloidal photonic crystals in a large‐scale and fast fashion. By integrating microfluidics‐derived photonic supraballs with supramolecular hydrogels, highly ordered photonic hydrogels with linear, planar, and spiral assemblies with flexible structures and angle‐independent spectrum characteristics can be easily achieved, which show great potentials in reflective cooling.
Amid increasingly stringent global environmental regulations, marine engines are undergoing an essential transition from conventional fossil fuels to alternative fuels to meet escalating regulatory ...requirements. This study evaluates the effects of injection pressure, the timing of ammonia injection, and the pre-injection of ammonia on combustion and emissions, aiming to identify optimal operational parameters for low-speed marine engines. A three-dimensional model of a large-bore, low-speed marine engine in a high-pressure diffusion mode was developed based on computational fluid dynamics (CFD). Simulations were conducted under 25%, 50%, 75% and 100% loads with a high ammonia energy substitution rate of 95%. The results indicate that, compared to traditional pure diesel operation, adjusting the injection pressure and the ammonia injection timing, along with employing appropriate pre-injection strategies, significantly enhances in-cylinder pressure and temperature, improves thermal efficiency, and reduces specific fuel consumption. Additionally, the dual-fuel strategy using diesel and ammonia effectively reduces nitrogen oxide emissions by up to 37.5% and carbon dioxide emissions by 93.7%.
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