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Fracture permeability is one of the critical factors affecting thermal production in hot dry rock reservoirs. Mechanical creep can cause temporal reduction of fracture permeability. However, the study solely on mechanical creep is limited, particularly under high confining stress. In addition, a physics-based stress- and time-dependent permeability model is essential for predicting the in situ geothermal production. This work aims to study the mechanical creep on the time-dependent fracture permeability. Long-term flow tests through single fractured granite samples under constant loading (20, 35, and 50 MPa, respectively) and stepwise increased loading (20 → 35 → 50 MPa) were conducted. The influence of the loading stress on the creep rate and the influence of the time on the permeability damage were quantitatively investigated. Based on the experimental data, a permeability model considering both stress and time effects was established based on viscous–elastic mechanics. According to the study, we obtained the following conclusions: (1) A higher constant confining stress can result in larger creep deformation, a larger damage ratio of hydraulic aperture (eh), and a longer duration of rapid reduction of eh. (2) The previously accumulated creep deformation can affect the subsequent time effect on the temporal evolution of eh when the loading stress changes, causing eh rapid reduction stage to weaken or disappear. (3) The transient creep behavior of eh can be described by the Kelvin creep model, and the maximum damage caused by the creep deformation is almost linearly proportional to the loading stress. The increase in stress caused by the bridging effect between adjacent contact asperities can dramatically reduce the creep rate. (4) The established permeability model can effectively predict the permeability with change in both stress and time considering the effect of accumulated creep deformation on the subsequent creep deformation, and it can be easily implemented in numerical simulation. [ABSTRACT FROM AUTHOR]

Water flow experiments in single tensile and shear granite fractures were conducted to investigate the nonlinear flow behavior. Fracture geometry parameters based on single fracture wall (Rp, Z2, Z3, Z4, JRC) and two fracture walls (aperture distribution, cluster coefficient) were calculated and compared. The effect of these fracture geometry characteristics on nonlinear flow behavior was explored. Fracture transmissivity, critical Reynolds number, pressure gradient, and normalized transmissivity were analyzed in detail. The result shows that shear fracture geometry has the characteristics of higher mean aperture with higher standard deviation, more clustering contact, and rougher fracture surface. The shear to tensile fracture transmissivity ratio increases from 2.3 to around 370 with the increase of confining pressure from 2 to 60 MPa and the stress-dependence coefficient of shear fractures is close to 1/22 of tensile fractures. The critical pressure gradient increases as confining pressure, indicating that it requires a higher pressure gradient to drive the linear flow to nonlinear flow, namely, when the injection pressure gradient keeps unchanged, high confining pressure causes the nonlinear flow to turn to linear flow. The critical gradient of the shear fracture is 0.004–0.527 MPa/m on average, which is much lower than that of tensile fractures (0.011–26.862 MPa/m), meaning that a lower pressure gradient can drive the linear flow to nonlinear flow in a shear fracture. The average Forchheimer coefficient β for tensile fractures is 0.133, which is about half of the shear fracture (0.253). Regression analysis indicates that a linear relationship exists between β and the fracture geometry parameters (mean aperture η and cluster coefficient ς) and the correlation coefficient is about 0.925 and 0.920, respectively. Further investigation confirms the "weak inertial effect" with the (T0/T − 1)/Re data points falling in a straight line before the "strong inertial effect," where the data points fall in an approximately horizontal line. [ABSTRACT FROM AUTHOR]

Hydraulic fracturing has been proven to be the most efficient way to improve the permeability of coal seams. In this work, the hydraulic fracture propagation in an underground coal mine was numerically investigated. A new numerical approach was developed based on the equivalent continuum methodology to model the hydro-mechanical behavior of multiple fractures in three dimensions. It was solved using a hybrid combination of the embedded element method (EEM) and the finite volume method (FVM) using an iterative coupling schema. The FVM was employed to calculate the pressure field, while the EEM was used to track the displacement discontinuity caused by fractures. A fracture constitutive model was implemented to describe the aperture variation, shear slippage, and shear dilation for both contact and open fractures, as well as for contact and open criteria. To verify the developed model, two benchmark examples were presented. Then, the developed model was used to numerically investigate hydraulic fracture propagation in Datong underground coal mine in Songzao in Chongqing. According to the numerical study, it was found that (1) a fracture network created by a hydraulic fracturing operation in a coal mine is more complex than the ideal cross-cutting-shape, H-shape, T-shape, and Z-shape patterns; (2) the orientation of the minimum principal stress controlled the main propagation direction; (3) the complexity of the fracture pattern is controlled by the geological structure, the in situ stress and the injection rate. [ABSTRACT FROM AUTHOR]

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 NH 2 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. [ABSTRACT FROM AUTHOR]

Fossil resins are often used to indicate the botanical origins of ancient plants through their secondary metabolites. However, the existing chemotaxonomy of fossil resins is limited in its ability to distinguish them at phylum, family, and genus levels using small amount of samples. Herein an advanced head-space solid phase microextraction- comprehensive two-dimensional gas chromatography- time-of-flight mass spectrometer platform was established to analyze the complex compositions of resin fossils derived from ancient gymnosperms (e.g., Eocene Cupressaceae , Cretaceous Araucariaceae) and angiosperms (Miocene Dipterocarpaceae and Miocene Hymenaea). The secondary metabolites including 83 monoterpenes, 186 sesquiterpenes, 84 diterpenes, and 43 n-alkanes were annotated and then chemically fingerprinted for the first time. Prior to conducting chemical composition classification, this study tested the vitrinite reflectance of resin-bearing rocks and Tmax of the ambers to demonstrate their similar thermal maturity. After that, chemotaxonomic markers were disclosed using multivariate statistical analysis to identify the botanical origins of resin fossils, and four identification rules were concluded. Gymnosperm and angiosperm resins can be distinguished by the relative content of monoterpenes and diterpenes. Eocene Cupressaceae and Cretaceous Araucariaceae resins can be identified by ten chemotaxonomic markers which were screened out by orthogonal partial least-squares regression. Miocene Hymenaea and Dipterocarpaceae resins have different combinations of chemical superclasses, with sesqui- and di-terpenes being the major compositions of Hymenaea resins, and mono- and sesqui- terpenes accounting for most of the compositions of Dipterocarpaceae resins. Specific chemotaxonomic markers can identify Hymenaea mexicana and Hymenaea protera resins. As the chemical components of fossil resins were determined by the genes present in their botanical origins, the chemotaxonomic markers revealed in this study have a genetic basis. These findings provide a comprehensive database of secondary metabolites from ancient resin plants, which can be utilized for further research on their corresponding paleoenvironment and to clarify their phylogeny. [ABSTRACT FROM AUTHOR]

We present a dynamically frequency tunable Fano resonance planar device composed of periodically asymmetric graphene nanodisk pair for the mid-infrared region. The two asymmetric graphene nanodisks can be directly excited by the light simultaneously and produce two kinds of reflected light with almost the same spectrum linewidth. By studying the local field distributions of our structure, we find that there are two kinds of modes for the two asymmetric graphene nanodisks, i.e., the symmetric mode and antisymmetric mode. Resonance coupling between the symmetric and antisymmetric modes generates the Fano resonance in our structure. This Fano resonance generation mechanism is different from it in traditional Fano resonance structure. In the traditional Fano resonance structure, the Fano resonance comes from the coupling effect between continuum and discrete structure. Moreover, we find that 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 it. [ABSTRACT FROM AUTHOR]

To investigate the fractal characteristics of rock crack distributions during the loading process, discrete element method was used to make rock samples with joints and record the crack propagation. The Box-counting method was used to quantitatively analyze the fractal dimension of the crack distribution at each moment, and the relationship between the crack fractal dimension and strain ratio was established based on fractal theory. The results indicated that the relationship between the fractal dimension of the crack distribution and strain ratio showed a strong linear characteristic. By transforming this linear relationship into a linear function, the slope of the function was found to be linked to the failure patterns of the sample, and a refinement coefficient (damage-fracture reduction factor) was identified from the slope as an effective basis for determining the degree of sample damage and fracture. The damage-fracture reduction factor can be categorized: 0.25–0.5 (spilt and fracture), 0.5–0.9 (synergy between fracture and damage), 0.9–1 (microcrack asymptotic damage). Owing to the linear fractal characteristics, an expression for the damage variables influenced by failure patterns can be established from the geometric aspect. In addition, the linear fractal characteristics of the cracks were verified in other acoustic emission and crack extension experiments. [ABSTRACT FROM AUTHOR]

Gentiana dahurica Fisch. (G. dahurica) is one of the legitimate sources of Qinjiao in Traditional Chinese Medicine (TCM) and grows on high-altitude plateaus. Plants develop unique biochemical accumulations to resist plateau conditions, especially the strong UV irradiation. Thus, this study aimed to investigate the polysaccharide of G. dahurica (GDP), its structure and its activity against UVB irradiation. Four GDPs were isolated and two of them were subjected to structural elucidation. The results suggested that GDP-1 has 53.5 % Ara and 30.8 % GalA as its main monosaccharides, with a molecular weight (Mw) of 23 kDa; the GDP-2 has 33.9 % Ara and 48.5 % GalA, with a Mw of 82 kDa. Methylation and NMR spectroscopy analysis revealed that GDP-1 contains →5)-α-Ara f -(1 → 5)-α-Ara f -(1 → 3,5)-α-Ara f -(1 → 3,4)-α-Gal p A-(6-OMe)-(1→ as the main chain, the branches of GalA (with esterification), and the terminal Ara; the GDP-2 contains →4)-α-Gal p A-(1 → 4)-α-Gal p A-(6-OMe)-(1 → 5)-α-Ara f -(1 → 3,5)-α-Ara f -(1→ as the main chain, the branches of →5)-α-Ara f -(1–5)-α-Ara f , and the terminal GalA. Both GDP-1 and GDP-2 exhibited concentration-dependent antioxidant activity against DPPH, ABTS and hydroxyl radicals. Moreover, GDPs significantly attenuated the decreases in viability and proliferation of HaCaT cells after UVB irradiation. They can scavenge reactive oxygen species (ROS) and improve the activities of endogenous antioxidant enzymes, including superoxide dismutase (SOD) and glutathione peroxidase (GSH). The potential mechanism explored by flow cytometry assays of cell apoptosis and cell cycle distribution suggested that GDPs exert protective effects against UVB irradiation by reducing ROS and attenuating S phase cell arrest. In brief, the GDP-1 and GDP-2 are α-1,3- and α-1,4- arabinogalacturonan, respectively. The high content of Ara could be attributed to biochemical accumulation in resisting to the plateau environment and to prevent UVB irradiation-related damage in cells. These findings provide insight into authentic medicinal herbs and the development of GDPs in the modern pharmaceutical and cosmetics industry. [Display omitted] [ABSTRACT FROM AUTHOR]

Reducing recoil as well as reducing muzzle hazards are important issues in artillery design. This paper presents a barrel gas reflection method for the artillery aiming for efficient recoil reduction while reducing muzzle hazards. The launching process is modeled by coupling the interior ballistic equations and the flow equations of the barrel gas reflection device. The fourth-order Runge–Kutta method was used to solve the model, and the LHS method as well as the Kriging model was used to establish a mapping relationship between the parameters and the effect. To validate the proposed model, shooting experiments are carried out on a 30 mm caliber artillery. The maximum error between the experiment and simulation results was 5.32%. The experiment has demonstrated that the barrel gas reflection method increases the recoil reduction efficiency of artillery by 44.54% and reduces the muzzle hazard by 52.18%. Finally, the barrel gas reflection method can produce effects with the muzzle device at the same time, and it has little effect on the velocity of the projectile muzzle velocity, and it provides a new way of thinking for the development of future artillery recoil reduction technology. [ABSTRACT FROM AUTHOR]

The fluid flow characteristics in shale fractures are of great significance for shale gas reservoir evaluation and exploitation. In this study, artificial tension fractures in shale were used to simulate the hydraulic fractures formed by fracturing, and a gas flow test under different pressure gradients was conducted. The nonlinear gas flow and stress‐dependent permeability characteristics were analyzed. The experimental results show the following: (a) CO2 flow in shale fractures exhibits strong nonlinearity. Forchheimer's law, which considers gas compressibility, satisfactorily describes the nonlinear relationship between the flow rate and the pressure gradients in shale fractures. (b) The permeability sensitivity of shale fractures under stress is very strong, and the exponential relationship better describes the pressure dependency of the permeability for the tested shale samples. The permeability of the shale fractures is similar when measured parallel or perpendicular to bedding. Furthermore, the pressure dependence of fractures in shale obeys the Walsh permeability model. (c) As the effective stress increases, the nonlinear flow behavior appears earlier. Based on the Reynolds number and the nonlinear coefficient, a friction factor model is proposed. (d) The normalized transmissivity exhibits a strong correlation with the Reynolds number. CO2 flow through shale fractures is generally dominated by transitional flow. The critical Reynolds number ranges from 1.8 to 102.88 and decreases with increasing effective stress. [ABSTRACT FROM AUTHOR]

Highlights: What are the main findings? The 3D stress distributions around the gob after mining are numerically calculated. What is the implication of the main finding? The propagations of hydraulic fractures in different disturbed areas caused by mining-induced stress are compared. The influence of the geological conditions that often appear in situ in hydraulic fracturing patterns in a hard roof is examined. 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. [ABSTRACT FROM AUTHOR]

An optically transparent metamaterial for microwave absorber with wide operation angle, polarization insensitivity, broadband and high absorptivity was demonstrated. The metamaterial is composed of planar indium tin oxide (ITO) structures and low-loss glass substrates. By tailoring the reflection response of ITO patterns and the position of arrayed ITO resonators between quartz glass dielectric substrates, more than 90% absorption in the frequency ranges of 8–20 GHz and within a wide angular range from 0° to 60° is achieved. Meanwhile, by employing transparent substrates, including soda-lime glass and quartz glass, good optical transmittance (80%) is obtained. The dielectric loss of quartz glass is lower than other dielectric substrates, which implies that the high absorptivity was achieved mainly due to the contribution of planar ITO metamaterial structure. The reflectivity of proposed MMAs is simulated and measured experimentally. Both of which demonstrate excellent absorption performance of the metamaterial. The optically transparent broadband metamaterials absorber with high absorptivity and polarization insensitivity opens a horizon of potential applications in many fields. • We report a metamaterial with more than 90% absorption in the whole frequency ranges of 8–20 GHz within a wide angular range from 0° to 60°. • By employing transparent substrates, including soda-lime glass, quartz glass and ITO structures, high optical transmittance (80%) is obtained. • Low-loss optical glass can be employed for high-performance electromagnetic absorber by designing the ITO structures and the position within the substrates. [ABSTRACT FROM AUTHOR]

• The microcapsules did not cause an apparent decrease in cell viability. • The 2-l-m were internalized into cells faster than the 10-l-m. • The microcapsules with more layers do affect the cytoskeleton structure. In this study, microcapsules with variable mechanical strength were fabricated by layer-by-layer (LBL) assembly based on MnCO 3 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. [ABSTRACT FROM AUTHOR]

The overwhelming majority of experimental and numerical tests show the dependence of mechanical response on discontinuities (such as joints, faults, and bedding plane). In this study, fracture process is numerically investigated using finite‐difference method. A quasi‐continuum model (assuming that the real rock mass represents the sum of intact rock and fracture) has been developed to describe the fracture propagation in a fractured rock. First, this model has been validated against the experimental results and was shown to simulate satisfactorily the fracture propagation in the tensile, shear as well as the mixed (tensile and shear) modes. This model then has been used to investigate the fracture processes during the 2D long‐wall mining and 3D pillar failure. According to the 2D and 3D simulations, it was found that: (a) this model can provide a new reasonable approach to simulating fracture processes in either 2D or 3D cases; (b) roof failure is mainly caused by shear fractures rather than tensile fractures during the 2D long‐wall mining. [ABSTRACT FROM AUTHOR]

Abstract: In the present study, diffusion bonding of Ti–6Al–4V alloy (TC4) and Oxygen Free Copper (OFC) by using a 0Cr18Ni9 stainless steel interlayer was investigated. The addition of 0Cr18Ni9 stainless steel interlayer improved the bonding quality. The element distribution, microstructure, compositions, mechanical properties and microhardness change of the bonded samples were studied by means of electron probe micro-analyzer (EPMA), scanning electron microscope (SEM), X-ray diffraction system (XRD) and microhardness. The results show that Ni3Ti, Fe2Ti, TiCr2 and FeTi formed at the TC4/0Cr18Ni9 interface show better mechanical properties than that of Cu–Ti compounds. Solid solutions are formed at the 0Cr18Ni9/OFC interface. The fracture of the joints had taken place through the TC4 and Ti–Fe compounds. The reaction process at the interface of TC4/0Cr18Ni9/OFC joints consisted of the physical contact stage, the generation of intermetallic compounds and the growth of intermetallic compounds. The tensile strength of joints increased firstly and then decreased with the rising bonding temperature. The sample bonded at 880°C for 30min under 5MPa shows the maximum tensile strength of 140.3MPa. There is a substantial improvement in the bonding quality, when its tensile strength is compared with 48.32MPa for directly-bonded TC4/OFC joint. [Copyright &y& Elsevier]

• Exploitation of deep geothermal energy in a multilateral-well EGS was studied. • A 3D THM coupled numerical model was proposed and implemented. • Thermal conduction and convection in both pore and fractures were considered. • Creation process of hydraulic fractures on heat extraction performance was studied. • A zipper fracture configuration is advantageous for efficient heat extraction. Studying the effects of physical-based hydraulic fracture configurations on heat extraction performance in a multi-lateral enhanced geothermal system (EGS) can provide meaningful suggestions for in-situ operations. In this work, we proposed a 3D thermal-hydro-mechanical (THM) coupled numerical model that is capable to simulate both hydraulic fracturing and heat extraction in dual porous and fracture medium. Using this model, the exploitation of deep geothermal energy in a multilateral-well EGS from creation and configuration of hydraulic fractures, to thermal extraction was simulated and comprehensively studied. Based on the results, the following conclusions were drawn: 1) configuration of fracture pattern in a multi-lateral well EGS was affected by in-situ geological conditions (e.g. in-situ stress state) and operation strategies (e.g. sequence of hydraulic fracturing operation, position of perforation for hydraulic fracturing etc.); 2) different fracture configurations lead to great differences in heat production. The final thermal power of the worst configuration was 5.55 MW, while that of the best configuration was approximately 7.25 MW in this study; 3) a zipper fracture configuration is advantageous for homogeneously heat reduction in the geothermal reservoir that is preferable for efficient heat extraction; 4) stress shadow induced by simultaneous hydraulic fracturing can be used to create a non-connected zipper fracture pattern that can improve the heat extraction performance in the fractures at the toe side. [ABSTRACT FROM AUTHOR]