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A hard roof can cause serious issues corelated with the stability of the panel including large deformation of the roadway in the gob, rock burst, coal and gas outbursts, etc. Currently, hydraulic fracturing has ever-increasingly been used to help control these above-mentioned issues in many engineering cases. This paper presents a series of numerical simulations for hydraulic fracturing with a recently developed model to examine the weakening effect of this pre-conditioning measure on a hard roof. The results show that large deflections in the principal stress direction occur above the coal seam after mining, which can be progressively enhanced as the working face continuously advances. This further could significantly affect the hydraulic fracturing pattern and result in arc-shaped fracture propagation, especially for the hydraulic fracture in stress-descending areas. The obtained results suggest that the hydraulic fracturing operation in a hard roof is preferable in the areas close to the middle of the gob where the created fractures would be deflected more. At last, sensitivity analysis shows that geological conditions have great influence on the hydraulic fracturing pattern. Among the factors analyzed in this paper, the difference between the maximum and minimum stress has the largest influence and should be fully considered. This study could provide a theoretical basis for the practical hydraulic fracturing operation in a hard roof.

The equipment of outdoor substations are operated in complex atmosphere and electromagnetic environments for a long time. They are often affected by these complex environments and special corrosion occurs, which is not conducive to long-term stable operation of the substation and may affect the quality of power. Therefore, it is necessary to explore the influence of various typical factors on the corrosion degree of substation equipment in complex environment. In this paper, the corrosion simulation of substation equipment is carried out by COMSOL software, and the influence of electromagnetic factors such as SO 2 , salt load and leakage current on the corrosion degree is explored. The study found that salt load, SO 2 and pH can significantly accelerate the corrosion of the equipment, and the degree of influence is large.

Reduced graphene oxide/titanium dioxide nanotube (rGO/TNT) composites have superior properties, such as a large surface area, extraordinary mechanical strength, high carrier mobility, etc. However, the biosafety and biocompatibility of these composites, such as their influences on cell viability and cell functions, which are of paramount importance, are still not fully addressed. In this study, rGO/TNT nanocomposites were successfully synthesized through a modified hydrothermal treatment method. Then, the interactions between the rGO/TNT nanocomposites and Raw264.7 mouse monocyte-macrophage cells were further investigated. The results show that the rGO/TNT nanocomposites could be internalized by Raw264.7 cells and mainly gathered inside the cytoplasm. No rGO/TNT nanocomposites were observed in the nucleus. Moreover, the rGO/TNT nanocomposites exhibited low cytotoxicity toward Raw264.7 cells at a lower dose, though they may exhibit cytotoxicity to some extent at very high concentrations. In addition, the uptake of the nanocomposites influenced the cell cytoskeleton organization, while the cell adhesion and migration abilities were also impaired.

In this study, microcapsules with variable mechanical strength were fabricated by layer-by-layer (LBL) assembly based on MnCO3 templates, and the influence of microcapsule stiffness on cellular uptake and cell functions were investigated. The microcapsules were well dispersed in water and had a spherical form of a uniform size. The average layer thickness was calculated to be 18.4 ± 0.4 nm, while the elasticity modulus of the 2- and 10-layer microcapsules was measured to be 1243.3 ± 212.0 and 3309.5 ± 505.7 MPa, respectively. The influence of the microcapsules uptake on cell viability and functions was then studied in terms of cell viability and cytoskeleton organization. The uptake of the microcapsules did not cause an apparent decrease in cell viability or alteration of cell morphology but did change the cytoskeleton organization to some extent.

The position and attitude measurement of space object is a key problem in the field of real-time navigation, modern control and motion tracking. As a non-contact position and attitude estimation method, machine vision position and attitude estimation has the advantages of simple structure and convenient measurement. This paper presents a vision positioning system and method based on multiple reference markers. The camera moving along the object continuously collects images containing reference markers from the camera's field of view．The spatial position information of reference mark is determined in advance, and the position and direction of moving target are calculated according to location and attitude algorithm. The main contribution of this paper: first, a plurality of reference markers is arranged in the range of moving objects so as to enlarge the range of visual positioning; second, when more than one reference marker appears in the field of view, it is possible to improve the positioning accuracy by selecting the marker of the larger contour area or the marker of the distance closer to the imaging plane principal point; third, we use the decoder to transform the reference marker into digital number. This method can improve the robustness of the system.

Polymer-functionalized graphene oxide (GO) has superior properties such as large surface area, extraordinary mechanical strength, high carrier mobility, good stability in physiological media and low cytotoxicity, making it an attractive material for drug and gene delivery. Herein, we successfully synthesized GO with an average size of 168.3 nm by a modified Hummers' method. Branched polyethylenimine (PEI) and 6-armed polyethylene glycol (PEG) functionalized GO complexes (GO-PEI and GO-PEG) with different zeta potentials of 47.2 mV and −43.0 mV, respectively, were successfully synthesized through amide linkages between the COOH groups of GO and the NH2 groups of PEI and PEG. Then, the interactions between GO-PEI and GO-PEG complexes and Raw264.7 mouse monocyte-macrophage cells were investigated. The GO-PEI and GO-PEG complexes could both be internalized by Raw264.7 cells. However, compared with the GO-PEG complex, the GO-PEI complex showed higher intracellular delivery efficiency in Raw264.7 cells. Moreover, it was found that the GO-PEI complex not only gathered in endosomes but also in the cytoplasm, whereas GO-PEG gathered in endosomes only. The MTT tests showed that both GO-PEI and GO-PEG complexes exhibited very low cytotoxicity towards Raw264.7 cells when at a low concentration. The cellular immune response test demonstrated the GO-PEG complex enhanced the secretion of IL-6, illustrating it was more stimulus towards macrophage cells. The above results indicated that the GO-PEI complex, with a positive surface charge, demonstrated better potential to be used in effective drug and gene delivery.

In this letter, we introduce stacked fishnet metamaterial for steering light in microwave region. We numerically demonstrate that optical Bloch oscillations and a focus of as small as one sixth of a wavelength can be achieved. The flexibility of varying geometrical parameters of the fishnet slabs provides an efficient way for tuning its local effective media parameters and opens the possibility for controlling light arbitrarily. The experiment verifies subwavelength-sized light focusing effect by scanning magnetic field at the surface of the sample directly.

We present a dynamically frequency tunable Fano resonance planar device composed of periodically asymmetric graphene nanodisk pair for the mid-infrared region. There are two kinds of modes in this structure, that is, the symmetric mode and the antisymmetric mode. The resonance coupling between the symmetric and antisymmetric modes creates a classical Fano resonance. Both of the Fano resonance amplitude and frequency of the structure can be dynamically controlled by varying the Fermi energy of graphene. Resonance transition in the structure is studied to reveal the physical mechanism behind the dynamically tunable Fano resonance. The features of the Fano resonant graphene nanostructures should have promising applications in tunable THz filters, switches, and modulators., Comment: 8 pages, 4 figures

The quasi‐isentropic loading technique allows investigation of material properties in a high‐pressure, low‐temperature regime that is inaccessible by conventional shock wave experiments. In the present paper, the layered flier‐plate and graded density flier‐plate, which have different variations in the density gradient along the thickness direction but the same density range, were designed and fabricated. Impact experiments were then performed on a two‐stage light gas gun. VISAR‐measured results show that wave profiles with an initial jump followed by a slowly‐rising front to the peak velocity amplitude are generated by using both types of the flier‐plate, indicating that quasi‐isentropic loading to the targets have been successfully realized. The process of quasi‐isentropic loading can be seen as the successive overlap of a series of small shock waves by the transient layers in the flier‐plate. It is obvious that the graded density flier‐plate creates a more smoothly rising front, and the compression effect must be closer to isentropic loading than that of the layered flier‐plate with the same density range.