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Purpose. To analyze the coupling effect between composite slope geometrical parameters. Methods. The slope angle and excavation depth are coupled with load which is waste dump in this case. Several models were created and analyzed to capture their coupling effect and interactions using FLAC/Slope. Findings. When the slope angle and excavation depth are coupled with a load such as that of a waste dump, the factor of safety decreases. But a suitable dumping position can prove vital to enhancing stability. The primary cause of this phenomenon is that the stresses induced by the waste dump decrease as the dump is moved away from the crest of the slope and the stress induced within the zone of active wedge beneath the dump reduces on the reference slip plane. Hence, it can be said that the position of the waste dump in the formation of a composite slope plays a key role in enhancing stability. Factor of safety have the same influence pattern for all parameters induced by stress as that of influence rule. The results obtained from the finite element stress analysis are the same with those obtained for the slope stability analysis. Originality. The current research presents for the first time the coupling effect of the composite slope geometrical parameters and the results of finite element stress analysis, which are similar to those of slope stability analysis. Practical implications. The current research results can be used to effectively analyze and design the composite slopes in soft rocks specially in surface mines.

In this paper, the dilatancy stress and mechanical characterization of sandstone were evaluated under uniaxial loading at different elastic modulus and porosity conditions. The prediction model of dilatancy stress was established using a regression equation and an artificial neural network based on a multilayer perceptron (ANN–MLP). The results indicate that: (1) The rock crack initiation stress, dilatancy stress and its elastic modulus are a power function relationship, while porosity is linearly negatively correlated. (2) σci/σmax hardly changes with the change of elastic modulus (E) and porosity (n); its value is about 0.443. σcd/σmax increase with the increase in the elastic modulus, but decrease with the increase in the porosity. (3) Most of the rock samples are observed as a tensile failure when the porosity is low, while they are a shear failure at medium porosity and tensile shear composite failure at high porosity. (4) The optimum value from the ANN–MLP model for dilatancy stress with architecture 6-5-1 having coefficient correlation (R2, 0.96%) was obtained at mean absolute error (MAE, 0.18981) and root mean square error (RMSE, 0.17016). It is worth mentioning that the research results will help and provide a reference for the related to rock mechanics test, rock engineering deformation and failure mechanism, and will also give specific guidelines significance for the efficient design of excavation and support in deep rock engineering.

A metasurface absorber based on an electro-optic (EO) substrate is numerically investigated. Flat resonant peaks are achieved in both visible and infrared regions. The spectral widths are 1012 and 556 nm, respectively, at 70% and 90% of absorption level in the waveband of 500–2000 nm. The actual absorption efficiency is calculated as 71.56%, being about that of high-efficiency multilayer absorbers. The design is characterized for its thin-metallic substrate and a spectral width of 229 nm at 98% absorption level at a single resonant mode is observed. The EO substrate is used to tune the wavelengths to the desired region of absorption by varying the applied voltage in order to reduce the use of scaling and fabrication complexities. The broad resonances can be used for power harvesting and solar thermals. Moreover, the EO-based tunability can find applications in infrared detection and optical filtering.

Novel approaches to synthesize efficient inorganic electride [Ca24Al28O64]4+(e−)4 (thereafter, C12A7:e−) at ambient pressure under nitrogen atmosphere, are actively sought out to reduce the cost of massive formation of nanosized powder as well as compact large size target production. It led to a new era in low cost industrial applications of this abundant material as Transparent Conducting Oxides (TCOs) and as a catalyst. Therefore, the present study about C12A7:e− electride is directed towards challenges of cation doping in C12A7:e− to enhance the conductivity and form target to deposit thin film. Our investigation for cation doping on structural and electrical properties of Sn- and Si-doped C12A7:e− (Si-C12A7:e, and Sn-C12A7:e−) reduced graphene oxide (rGO) composite shows the maximum achieved conductivities of 5.79 S·cm−1 and 1.75 S·cm−1 respectively. On the other hand when both samples melted, then rGO free Sn-C12A7:e− and Si-C12A7:e− were obtained, with conductivities ~280 S.cm−1 and 300 S·cm−1, respectively. Iodometry based measured electron concentration of rGO free Sn-C12A7:e− and Si-C12A7:e−, 3 inch electride targets were ~2.22 × 1021 cm−3, with relative 97 ± 0.5% density, and ~2.23 × 1021 cm−3 with relative 99 ± 0.5% density, respectively. Theoretical conductivity was already reported excluding any associated experimental support. Hence the above results manifested feasibility of this sol-gel method for different elements doping to further boost up the electrical properties.

We theoretically propose a sensitive label-free sensor with high figure of merit (FoM) based on Fano resonances on a plasmonic metasurface whose unit cell consists of double two-split nanorings by finite-element method. The unit cell of the proposed Fano resonant structure comprises of two thin gold nanorings each with two splits. Two Fano modes are generated in near-infrared regime through symmetry breaking by rotating the splits in nanorings in opposite directions. The fundamental feature of the proposed sensor is its relatively simple structure, double-mode usable, a large single-side quality factor of 566, and high FoM value of 378. According to our knowledge, these values are higher than those previously reported. The sensor has high substance resolving capability that its minimum detectable refractive index change can be as small as 0.00236, making it possible to distinguish different bio-tissues.

The deformation and failure of rock materials are closely related to the strain energy characteristics during the loading process. These strain energy characteristics and rock properties are greatly affected when the rock is subjected to the acidic solution. To study the effects of chemical solutions with different pH on the mechanical properties and strain energy mechanism of mudstone, the chemical corrosion mudstone samples are subjected to a uniaxial loading testing machine (CN64 electro-hydraulic servo). The corrosive effects of the acidic solution on the porosity, strain energy characteristics, and failure mode of mudstone samples were thoroughly investigated. The findings of this research indicate that: (1) The rate of change in the porosity and chemical damage coefficient of rock samples after chemical corrosion decreases, which is closely linear with the increase of solution pH, (2) The total strain energy, elastic strain energy, and dissipative strain energy decrease with the increase of pH, and, as a result, it is proposed that the observed turning point of the proportion curve of dissipated strain energy from decline to rise is used as a precursor point of the rock failure, (3) The stress value of the failure precursor point increases and the strain value decreases with the increase in pH value. However, the ratio of the stress value of the failure precursor point to the peak stress hardly changes with pH value, and its value is about 0.883, and (4) Rock samples soaked in a weak acidic chemical solution (pH 7.3 and 5.3) are damaged by tensile crack, while rock samples soaked in a strong acidic chemical solution (pH 3.3 and 1.3) are mainly damaged by the combination of tensile and shear. The findings of this study can be used to provide an experimental and theoretical foundation for monitoring rock engineering disasters such as slope, tunnel, and coal mine failures.

In this study, a uniaxial impact compression test was performed on coal samples with length-to-diameter L / D ratios of 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1 using a Φ 50 mm split Hopkinson pressure bar (SHPB) test system. This study researched the stress uniformity and deformation behavior of coal samples with different L / D ratios during dynamic compression, defined the stress equilibrium coefficient ξ , proposed a new method for determining whether a sample meets the stress uniformity hypothesis, and obtained the critical L / D ratio of 0.6 and the optimal L / D ratio of 0.3 or 0.4 for coal samples to obtain the stress equilibrium. The experimental results showed that the dynamic stress-strain curve of coal had an elastic stage, a plastic stage, and a failure stage. As the L / D ratio increased, the proportion of the elastic stage to the prepeak curve of the samples declined progressively; with an increase in the L / D ratio, the peak part of the curve also changed from “sharp” to “stagnated,” while an increase in the plasticity led to strain softening. As the L / D ratio of the samples increased, the average strain rate decreased approximately as a power function, and the decreasing trend was gradually reduced from 296.49 s−1 ( L / D =0.3) to 102.85 s−1 ( L / D =1), with a reduction of approximately 65.31%. With an increase in the L / D ratio, the peak strain gradually decreased exponentially. This study concluded that the SHPB test protocol design is of a certain reference value for low-density, low-strength, heterogeneous brittle materials, such as coal.

The influence of acid solutions was investigated on the mechanical properties of mudstone. Uniaxial compression tests on mudstone samples were conducted to determine the variations of relative mass, porosity, deformation, and strength characteristics of mudstone subjected to acidic solutions with different pH values. The change of pH, relative mass, and porosity of mudstone in the process of acid solution immersion was monitored during soaking. The mechanism of hydrochemical corrosion of mudstone samples was preliminarily discussed. The damage parameter was introduced based on the porosity rate. The results show that with increased solution acidity, the peak stress and elastic modulus decreased to different levels, while the peak strain increases in the rock samples. The increased chemical damage parameters reduce the mechanical parameters and increased the deformation parameters. On the basis of the mechanical test, considering the stress-strain relationship of rock in the compaction stage, a segmented damage constitutive model of rock based on chemical damage parameters is established, and the test results are verified. The results show that the correlation coefficient between the theoretical curve and the experimental data is as high as 0.98, and the model is suitable for the analysis of chemically corroded rock under the uniaxial compression test. The results provide a reference for the analysis and design of coal-bed methane wells where the rocks frequently become acidic during the production of methane.

Bi4Ti3O12 is an important lead-free ferroelectric material. Doping modification of Bi4Ti3O12 has attracted great attention to improving its performances. In this work, the effect of Sr dopants on the microstructure, dielectric, and conductivity of Bi4Ti3O12 ceramic was investigated by XRD, SEM, and AC impedance spectroscopy. Substitution of 1 at% Sr for Bi decreased the grain size, suppressed the dielectric dispersion of Bi4Ti3O12 ceramic at room temperature, and resulted in different effects on the conductivity of grains and grain boundaries. The conductivity of grains in Bi4Ti3O12 ceramic was increased by the small amount of Sr dopants in the whole experimental temperature range. While the grain boundaries of 1 at% Sr-doped Bi4Ti3O12 exhibited lower conductivity than pure Bi4Ti3O12 below ~380 °C and higher conductivity above ~380 °C. The experimental phenomena were interpreted in term of compensating defects for Sr dopants.

In the present study we synthesized conductive nanoscale [Ca24Al28O64]4+(4e−) (hereafter denoted as C12A7:e−) material, and reduced graphene oxide (rGO) was produced, which was unexpected; graphene oxide was removed after melting the sample. The conductivity of C12A7:e− composites synthesized at 1550 °C was 1.25 S cm−1, and the electron concentration was 5.5 × 1019 cm−3. The estimated BET specific surface area of the highly conductive sample was 20 m2 g−1. Pristine C12A7:e− electride was obtained by melting the composite powder, but the nano size of C12A7:e− particles could not be preserved; the value of conductivity was ∼28 S cm−1, electron concentration was ∼1.9 × 1021 cm−3, and mass density was 93%. For C12A7−xVx:e−, where x = 0.25 to 1, the conductivity improved to a maximum value of 40 S cm−1, and the electron density improved to ∼2.2 × 1021 cm−3; this enhancement in conductivity was also proposed by a theoretical study but lacked any associated experimental support.

During the stress-induced rock failure process, anomalies in the Infrared Radiation (IR) can be observed. To study the response relationships between rock IR temperature and spatial-temporal evolution process of cracks in sandstone, the IR and Acoustic Emission (AE) were both measured during uniaxial compression. The multi-frames accumulation average technology and background thermal noise correction method were used to correct the IR temperature. According to the AE results, the temporal evolution process of cracks was divided into six stages: initial crack closure, linear elastic deformation, micro-crack development, macro-crack initiation, macro-crack propagation, and macro-crack coalescence. It was found that the changing rate of the Average Infrared Radiation Temperature (AIRT) changed with the crack evolution stage changed, which could be regarded as a basis for dividing the evolution stages of rock cracks using IR. The accumulated energy density map of AE events was used to analyze the spatial distribution characteristics of cracks and determine the Low Damage Area (LDA) and High Damage Area (HDA) of the rock samples. It was found that the AIRT variations were consistent between LDA and HDA during the entire loading process. However, since the stage of micro-cracks development, the difference value in AIRT between LDA and HDA gradually increased with time. The research results can provide a reference for the study of the rock crack evolution process with the surface IR information and are helpful to the early warning of rock failure.

The Infrared Radiation (IR) on the surface of a rock being loaded will change significantly during its failure process. To effectively monitor and predict rock failure by the IR method, in this paper, the Infrared Radiation Variation Temperature Field (IRVTF) of rock under uniaxial compression was identified. It was found that some IRVTF thermal images were characterized by obvious temperature rise in the later stage of rock loading. The temperature distribution characteristics of IRVTF were analyzed. It was observed that the temperature of the IRVTF exhibited the logarithmic linear distribution within the selected statistical temperature range, with an average coefficient of correlation greater than 0.96. On this basis, the index of “Infrared Radiation b-value (bIR-value)” of rock under uniaxial compression was defined for the first time, and the threshold for identifying its sudden change was proposed. It was found that the sudden changes of bIR-value could be observed with the generation of large-scale micro-cracks. The average amplitude of the bIR-value at first sudden change for all samples was 16.58 times of the mean amplitude before the sudden change on average, which indicated the significance of the bIR-value sudden change. The first sudden change of the bIR-value was 22.5 s ahead of the peak stress on average, which could be used as a precursor of rock failure and instability. The findings of the research can help with the monitoring and early warning of surrounding rock instability in mines, tunnels, and other geotechnical projects.

We present an overview on our recent work about a number of metasurfaces and their applications in absorbers, biosensors, and nano modulators. High-efficiency absorption, high bio tissue sensitivity, and high-performance modulation are demonstrated. The results are interesting for various applications including photonic integrated circuits and devices for solar energy utilization, optical signal processing, optical computations, optical communications, inside-body examination sensing, bio tissue discrimination, and cancer disease diagnosis.

The rock failure process is always accompanied by dilatancy. This study investigated the average infrared radiation temperature (AIRT) characteristics in the rock dilatancy process. An Infrared Radiation (IR) dilatancy precursor point was found prior to the failure of the rocks under load. During the uniaxial loading process, the stress levels of upward-AIRT and downward-AIRT rock samples at the initial point of rock dilatancy were 0.74 σmax and 0.80 σmax, respectively. After rock dilatancy, the AIRT change rate of upward-AIRT sample increased by 1.48 × 10−4°C⋅s−1, and AIRT change rate of downward AIRT sample dropped by 1.29 × 10−4°C⋅s−1. From the initial point to the process reached rock failure, the AIRT change was almost linearly correlated with volumetric strain increment. Based on the IR thermogram, the IR hot spot was defined, and a new index—high temperature point scaling factor (HTPSF)—was proposed for qualitative analysis. The calculated HTPSF values of upward-AIRT and downward-AIRT rock samples at the IR dilatancy precursor point were 0.4 and 0.6, respectively. This study provides a new thought to determine the initial point of rock dilatancy.

Water saturated rock strain energy evolution was measured using infrared radiation (IR) under uniaxial load of sandstone samples. The variation in the characteristics of total strain, elastic strain, dissipated strain energies and maximum IR of saturated rock under stress were analyzed. The results reveal the degree of saturation has a significant effect on rock strain energy. The total strain and elastic strain energies correlated linearly negatively, dissipative strain energy were correlated exponentially negatively, and maximum infrared radiation variance (IRV) correlated quadratically at peak stress point with different degree of saturation of rock samples. The relationship between total strain, elastic strain energies, and ΔIRV was a linear function under different saturated conditions. It was found that there was a linear energy transfer and linear energy storage function in the rock. Based on linear energy transfer and storage, two coefficient in the presence of IR were introduced, i.e., the Total Energy Infrared Radiation Coefficient (TEIRC) and Energy Storage Infrared Radiation Coefficient (ESIRC). These can be used with variation in infrared radiation variance (ΔIRV) to determine total strain and elastic strain energies of saturated rock. Furthermore, a quantitative analysis index of energy dissipation infrared radiation ratio (EDIRR), i.e. the ratio of dissipative strain energy to ΔIRV, has been proposed which can be used to predict and identify the failures of saturated rock. The inflection point of rock EDIRR from horizontal to rapid growth can be regarded as the precursor point for rock failure, and the EDIRR mutation after the precursor point can be used as the new criterion to monitor rock failure and instability.

We report spectral splitting behaviors based on Fano resonances in a novel simple planar metasurface composed of gold nanobars and nanorings. Multiple plasmonic modes and sharp Fano effects are achieved in a broadband transmittance spectrum by exploiting the rotational symmetry of the metasurface. The transmission properties are effectively modified and tuned by modulating the structural parameters. The highest single side Q-factor and FoM which reaches 196 and 105 are observed at Fano resonances. Our proposed design is relatively simple and can be applied for various applications such as multi-wavelength highly sensitive plasmonic sensors, switching, and slow light devices.

We present a broadband absorber in tri-layer plasmonic metamaterials with an electro-optic material as a substrate to fine tune the resonances. Broad resonant absorption peaks are achieved in a structure with metallic pieces. In the wavelength range from 300 nm to 2200 nm, the absorption spectral width is calculated to be 1078 nm, 566 nm, 282 nm, 119 nm, and 78 nm with absorption levels of 75%, 90%, 94.6%, 98.6%, and 99.4%, respectively. The total absorption efficiency, of the structure is evaluated to be 71.43%, which approaches to the absorption efficiency of a complex design with over 40-pair layers. The wide incident angle, polarization-insensitive, broadband absorption can be utilized for energy harvesting and solar thermals. Moreover, the use of electro-optic substrate has the advantage and potential to reduce the use of scaling structures and fabrication errors, and tune the resonant wavelengths to the desired range for imaging and infrared detection applications.

A highly efficient and broad light absorber capable of wide-angle absorption in the visible and near infrared range is presented and numerically investigated for energy harvesting in a simple geometry. According to the calculated results, the proposed device has a peak absorption level of about 99.95%. The actual absorption efficiency is 76.35%, which is approaching that of complex multilayer absorbers with 88 layers working in the wavelength range of 300 nm to 2000 nm. The electro-optic material has the potential of shifting the absorption peak position, compensating fabrication errors and thus reducing the fabrication technique difficulties. Also, the high electro-optic tunability can be used for filters, infrared detection, and imaging applications. More directly, the proposed absorber can be potentially deployed in solar cells and solar thermals.