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Understanding the response law and mechanism of weak currents stimulated from coal under an impact load is significant for the prediction of coal bumps in deep coal mines. In this paper, the system for the weak current measurement of coal under an impact load is established and the response characteristics of weak currents induced by the deformation of coal under an impact load are investigated. Physical models are established to describe the process of charge transfer and explain the generation mechanism of those currents. The results show that a transient current is stimulated from the coal sample when an impact load is applied, and then, the current decays slowly, tending to be a stable value that is slightly greater than the background current. The weak current flows from the loaded volume to the unloaded volume of the coal and increases with the impact velocity in a negative exponential form. Analysis of weak currents using non-extensive entropy shows that the attenuation of the weak current obeys non-extensive statistical mechanics and the non-extensive parameter q is greater than 2. The carriers are mainly electrons, of which the distribution obeys the tip effect that electrons tend to enrich towards the tip of a crack. The generation mechanism of those weak currents induced by coal deformation is the instantaneous movement of electrons under a density difference caused by the tip effect. Research results can provide a new perspective to understand the electric phenomena of coal under an impact load as well as a new method for coal bump prediction.

In order to explore the evolution characteristics of multi-scale rock-like material failure, we studied the acoustic emission (AE) and electromagnetic radiation (EMR) characteristics of different scale rock-like materials by using the AE-EMR experimental system of coal and rock failure, and the AE and EMR response law of rockburst in mining sites was analyzed. The results show that under uniaxial loading, the stress–strain curve of the specimen has a compaction stage, linear elastic stage, elastic–plastic stage and failure stage. The cumulative AE count, AE energy and stress level of the specimen have an exponential relationship during loading and compression. The cumulative EMR counts of loading and unloading showed a trend of first decreasing and then increasing with the increase in stress level. Electromagnetic radiation and microseismic hypocentral distance show an abnormal change trend when rockburst occurs, and this abnormal phenomenon can be used as a precursor feature signal for rockburst monitoring and early warning.

Owing to the complexity of the electrochemical reaction types in lithium-ion batteries and the characteristics of nonlinear degradation, using physical models to describe the degradation process is often not accurate enough. This paper only analyzes from the perspective of data, through a data-driven method, extreme learning machine ( ELM ), to predict the remaining useful life (RUL) of lithium-ion. Firstly, the cycle charge and discharge data of lithium-ion battery are analyzed in depth to find the parameters which can indirectly characterize the degree of degeneracy of lithium-ion battery. The parameters with strong robustness to the actual capacity of lithium-ion battery are selected as indirect health indicators by correlation coefficient analysis. Then, the RUL prediction model based on ELM is constructed, which is trained and tested using the lithium-ion battery data sample set published by NASA. The results show that the RUL prediction method based on ELM can effectively predict the battery RUL, and the root mean square error (RMSE) can reach below 5 %.

The schematic diagram for the plating/stripping process of Zn. (a) Corrosion, by-products, and Zn dendrites are observed on a bare Zn electrode. (b) The Zn–THBA protective layer endows a dense and dendrite-free plating/stripping morphology.

Coal bumps occur frequently during coal mining, and monitoring of stress variations of coal mass is a prerequisite for coal bump prediction. To investigate a new method to reflect coal stress variation based on the pressure stimulated current (PSC), localized cyclic loading–maintaining–unloading experiments on coal samples were carried out and weak currents were measured. The response characteristics of PSCs with stress variations were analyzed, physical models showing the mechanisms of PSCs were established, and mathematical models explaining the relationships between PSCs and mechanical behaviors were derived. The results show that PSCs (tens of nA) flowing from the stressed volume to the un-stressed one can be observed upon load application. The currents are repeated with cyclic loading, load maintenance and unloading, which indicate that PSCs correspond well to stress variations. During loading, the PSC increases to a peak value at approximately 0.6 MPa and then it fluctuates until the stress stops increasing. When load is kept constant, the current decays exponentially to a stable value. During unloading, the PSC decreases at a lower rate when stress is greater than 0.6 MPa, after which it decreases at a higher rate to a minimum when stress is removed. Fitting results show that PSC increases exponentially with loading rate and that the stable current increases linearly with the maintained stress. Positive holes activated by the fracture of chemical bonds in the side chain of coal macro-molecules are believed to be the carriers, and the PSCs are generated due to the movement of the holes along stress gradients. Deduced formulas relating PSCs with coal mechanical behaviors show that PSC is proportional to strain rate; that is, PSC is inversely proportional to elastic modulus when stress rate is constant, as verified by the experimental results. These research results are expected to provide a new idea for monitoring of stress variations of coals during mining, which is significant for the prediction and early-warning of coal bumps.

Synthesizing hydroxy-functional linear copolymers with high molecular weights (Mn) and low branching degree (Den%) remains challenging, although there has been much headway in the area of functional copolymers. Here, we studied the effect of polymerization methods (one-step or two-step) and solvents (organic solvent: diphenyl ether or ionic liquids: [Cnmim]TF2N/BF4/PF6, n = 2, 4, 6, 8, or 10) on Mn and Den% of copolymers P(OA–GA) (1,8-octanediol adipate (O-A)/glycerol adipate (G-A)). The Mn of P(OA–GA) reached up to 53 937 g mol−1 in two-step in diphenyl ether, and the Den% of glycerol can be controlled within 30%. The physical properties of these copolymers were investigated by contact angles, differential scanning calorimetry (DSC), and in vitro biodegradation. With increasing glycerol content in the polyesters, both hydrophilic properties and degradation properties increased. This system not only facilitates the synthesis of functional polyesters with high molecular weight and low branching, but also expands the possibility of using bio-based monomers to synthesize functional polymers.

The roles of mitochondrial respiration in pluripotency remain largely unknown. We show here that mouse ESC mitochondria possess superior respiration capacity compared to somatic cell mitochondria, and oxidative phosphorylation (OXPHOS) generates the majority of cellular ATP in ESCs. Inhibition of OXPHOS results in extensive pluripotency and metabolic gene expression reprogram, leading to disruption of self-renewal and pluripotency. Metabolomics profiling identifies UDP-N-acetylglucosamine (UDP-GlcNAc) as one of the most significantly decreased metabolites in response to OXPHOS inhibition. The loss of ESC identity induced by OXPHOS inhibition can be ameliorated by directly adding GlcNAc both in vitro and in vivo. This work demonstrates that mitochondrial respiration, but not glycolysis, produces the majority of ATP in ESCs, and uncovers a novel mechanism whereby mitochondrial respiration is coupled with the hexosamine biosynthesis pathway to generate UDP-GlcNAc for ESC identity maintenance.SIGNIFICANCEOxidative phosphorylation (OXPHOS) and glycolysis are the two major pathways for generating ATP in mammalian cells. It is widely assumed that somatic cells utilize OXPHOS, whereas embryonic stem cells (ESCs) utilize glycolysis with low mitochondrial respiration rates even under aerobic conditions. However, the relative contribution of OXPHOS and glycolysis to ATP generation in ESCs, and the role of mitochondrial respiration in regulating ESC identity, have remained unclear. In this study, Cao et al demonstrate that mouse ESC mitochondria have a significantly higher respiration capacity than somatic cell mitochondria. Oxidative phosphorylation produces the majority of cellular ATP in mESCs and is coupled with the hexosamine biosynthesis pathway to generate UDP-GlcNAc for pluripotency maintenance. These findings define the function and mechanism of OXPHOS in regulating pluripotency, and challenge the traditional concept that mESCs rely on glycolysis over OXPHOS for their major supply of energy.HIGHLIGHTSESC mitochondria have a significantly higher respiration capability than somatic cell mitochondriaOXPHOS, but not glycolysis, produces the majority of cellular ATP in ESCsOXPHOS inhibition induces a decrease in O-GlcNAcylation and the expression of pluripotency genes in blastocysts that can be partially rescued by adding GlcNAcOXPHOS is coupled with the hexosamine biosynthesis pathway for UDP-GlcNAc biosynthesis to maintain ESC identity

The differences between mechanical properties and acoustic emission (AE) and electromagnetic radiation (EMR) characteristics of natural coal samples and saturated coal samples were analyzed by performing indirect tensile experiments. The experimental results show that coal samples go through four stages: compaction, elastic deformation, plastic deformation and failure. There is good correspondence between AE and EMR signals and the damage to coal samples. Under the action of water, tension strength of samples is reduced, while the plasticity is enhanced; also, the softening coefficient of tensile strength becomes 0.65. The saturated coal samples have a longer plastic stage and a more obvious AE quiet period. The damage to natural coal samples is tension damage, while that of saturated coal samples is due to tension and shear damage, which is more sufficient and irregular. EMR is still remarkable when AE is in a quiet period, and EMR is better for the precursor of rupture. Water weakens the generation and propagation of AE and EMR signals, especially in the earlier stage. AE and EMR damage factor D, defined by AE and EMR counts, has a better description of the damage degree in the indirect tensile process. This study is of great significance for research on the damage mechanism of water-bearing coal, the stability monitoring of water-bearing coals in the actual engineering process and the effect evaluation of hydraulic flushing.

To study the influence of hydraulic slotting inclination on the mechanical behaviors of coal seam during mining process, uniaxial compression experiments on coal specimens with a single pre-existing flaw inclined at 0°, 15°, 30°, 45°, 60°, 75°, 90° and intact specimens were conducted. Acoustic emission (AE) signals in the loading process were monitored, and fractal analysis method was introduced to investigate the AE characteristics. Additionally, the laboratory experiments were simulated by a finite element code. Both the experimental and numerical results show that the existence of a flaw reduces the mechanical properties of coal. The uniaxial compressive strength and modulus of elasticity increase polynomially and linearly with the increase of inclination angle, respectively. When the coal specimen ruptures finally, the fewer the surface secondary cracks or the more the sudden drops of stress, the smaller the peak value of AE count. According to the stress–strain curve, the loading process is divided into five stages: (I) compaction stage; (II) linear elastic stage; (III) stable crack propagation stage; (IV) accelerating crack propagation stage; (V) post peak and residual stage. AE fractal characteristics in various stages of each specimen were determined by Grassberger and Procaccia algorithm based on phase space reconstruction theory. AE count show fractal characteristics from stage III. The fractal dimension declines rapidly in stage IV, and continues to decline further or rise slightly in stage V, but both are lower than that in stage III. Therefore, the changing rule of AE fractal dimension in different loading stages can be used as a precursor to coal and rock dynamic disasters.

A large amount of gas, which will do great damage to the environment as a kind of greenhouse gas, is discharged directly into the air in the process of coal mining in China. Majority of coal mines in China are characterized by low permeability, great gas pressure, and low strength feature. These features make it difficult for the extraction of gas, which increases the risk of coal and gas outbursts. In order to improve the permeability of coal seam, hydraulic flushing (HF) technology is adopted. So, the effect of hydraulic flushing will be necessary to be analyzed before gas extraction. In this paper, an electromagnetic radiation (EMR) experiment system of coal seam during hydraulic flushing was established, electromagnetic radiation (EMR) signals produced by the deformation and fracture of coal were studied during hydraulic flushing in coal seam in the Songhe coal mine, Guizhou province, China. The results showed that abundant EMR signals could be produced because of coal deformation and fracture. EMR signals were positively associated with the degree of coal failure. In different coal seams, EMR signals had different features during hydraulic flushing. The greater the gas pressure in the coal seam, the more dilatation energy was released. Higher rupture velocity could generate stronger magnetic signals. During hydraulic flushing, the more serious the rupture of coal, the higher the count of EMR pulses, and the higher the frequency of EMR. The principal frequencies and the amplitudes of waves increased gradually with gradually increasing ruptures. The change of EMR signals after hydraulic flushing was more dramatic than before hydraulic flushing. So, it is feasible and dependable to evaluate the effect of coal seam hydraulic flushing by EMR.

Although rechargeable aqueous zinc batteries (RAZB) have experienced their renaissance recently, Zn-metal anodes still suffer from serious dendrites growth and inevitable Zn corrosion in mild aqueous electrolyte during cycling. It is imperative to provide a simple and effective strategy to address the above problems. Herein, we have developed a one-step strategy to in-situ fabricate a homogeneous and stable protective layer composing of dense ZnF2 and embedded Cu particles on the electrode at room temperature. The ZnF2-Cu protective layer with both high Zn2+ transfer number (0.758) and homogeneous nucleation sites (Cu particles) with excellent zinc affinity exhibits remarkable synergistic effect for dual purpose: 1) to effectively inhibit severe dendrites growth via regulating Zn nucleation and 2) to suppress Zn corrosion and the accompanying hydrogen evolution by preventing Zn metal surface from aqueous electrolyte attacking. As a result, the ZnF2-Cu@Zn anodes can maintain stable cycling for>1600 h with super low over-potential and increased average coulombic efficiency (CE). In addition, the ZnF2-Cu@Zn || V2O5 full cells provide a reversible capacity of 103 mA h g−1 after 2000 cycles at an ultra-high current density of 10 A g−1. This work proposes a promising approach for the practical application of RAZB in the future.

The coordination of valeric acid (VA), glutaric acid (GA), and tricarballylic acid (TA) with Fe–OH on the Fe3O4 nanoparticle surface has been systematically studied to elucidate the effects of COOH, molecular configuration, and ligand concentration on the coordination by the combined use of attenuated total reflectance Fourier transform infrared (ATR-FTIR) and thermogravimetric analysis (TGA). The results show that the binding ability of the acids increases with the increase in the COOH number. Multiple conformations coexist for the dicarboxylic and tricarboxylic acid coordinated on the iron oxide NPs. Saturated coordination formed with only a one-, two-, or three-COOH conformation for VA, GA, and TA, respectively, occurs under ligand-scarce conditions, while unsaturated coordination formed with the mixture of uncoordinated, one-, and/or two-COOH conformations for VA, GA, and TA, respectively, exists under ligand-abundant conditions. The maximum coordination numbers for monolayer adsorption for VA, GA, an...

Electromagnetic radiation (EMR) anomalies preceding or accompanying coal and rock dynamic disasters have been reported for many years, but the mechanism that produces these anomalies is still unclear. To investigate the role that charge separation plays in these electromagnetic (EM) anomalies, uniaxial compression experiments on three different brittle materials: coal, marble, and polymethyl methacrylate were conducted. The results of the experiments indicate that EMRs are observed in piezoelectric and nonpiezoelectric materials but EM anomalies are only observed when abrupt stress drops occur. The EMR energy rate increases with the magnitude of the stress drop, and those two variables are related by a polynomial function. The charge separation responsible for the anomalies occurs on the newly generated cracks when chemical bonds are broken. A charge distribution model has been established for this phenomenon. Based on this model, the coupling relationship between EM energy density[Formula: see text] and charge density [Formula: see text] has been determined by theoretical analysis. According to this analysis, [Formula: see text] is proportional to [Formula: see text]. In addition, the relationship between [Formula: see text] and surface energy has been established, and it indicates that [Formula: see text] increases with (1) the stress to which the surrounding material is subjected and (2) the length of newly generated cracks. Research findings reported should provide a more detailed understanding of the EM anomalies when coal and rock dynamic disasters occur and provide guidance for developing warning strategies for mine safety.

Chinese coal mines often apply hydraulic flushing technology for pressure relief and permeability increase of difficult-to-extract coal seams In order to study effective detection methods for the impact range of hydraulic flushing on coal seams, we first experimentally investigated the response characteristics of the apparent resistivity of small-scale coal mass to hydraulic flushing, then theoretically analyzed the characteristics of its temporal variation and spatial distribution, and lastly measured the changes in apparent resistivity in the Hydraulic flushing process at Nuodong Coal Mine, Guizhou Province , China, and the effective range of Hydraulic flushing in the coal bed. The experimental results showed that the spatial distribution and variation of coal and rock mass structure could be reflected by apparent resistivity. Under high-pressure water, coal structure was changed (loosen, broken, or out-washed), forming cavities and a network of cracks in the surroundings of the drilling borehole , which reduced the conductivity of coal and caused a significant increase in apparent resistivity. In both laboratory and field experiments, the coal/rock apparent resistivity was relatively consistent, and the apparent resistivity in the hydraulic flushing impact region significantly grew. The hydraulic flushing impact range was gradually increasing, and the response of apparent resistance was closely associated with the role of high-pressure water and the evolution of the fracture field.

During the process of cross-cut coal uncovering, the stress and gas pressure of the coal mass change with time and even lead to coal and gas outburst. This paper establishes a coupled model that includes the equation of coal deformation, gas diffusion , gas seepage and permeability evolution based on the dual poroelastic theory. This model is applied into COMSOL Multiphysics numerical software. The distribution and evolution of the stress and gas pressure in front of the working face can be obtained from the numerical results. The stepped increase mechanism of the combined potential energy in the tunneling process is proposed, which is used to analyze the evolution of elastic potential energy and gas potential energy. The results can be summarized as follows: under natural conditions, an obvious abnormal stress area occurs near the fault, and the stress of the coal seam is greater than that of the rock stratum. Under tunneling conditions, a original stress (OS), stress concentration (SC) and stress reduction (SR) are formed successively in the front of the working face. And correspondingly, the gas accumulates in SC due to the closure of cracks. The distributions of gas pressure p f and p m are approximately the same during tunneling, and they can reach an equilibrium state after 300 days. The coupled effects of stress and gas pressure gradually intensify, so the elastic potential energy and the gas potential energy of the coal continuously accumulate. The combined potential energy of coal increases with tunneling length, and an outburst is very likely to occur when the combined energy exceeds the surface energy of the coal body at the “Key point”. This research is helpful to understand the evolution mechanism of stress and gas pressure of coal seam in the process of cross-cut coal uncovering, and to know the effects of it to the dynamic disaster.

Hydraulic flushing in gas predrainage is widely used, but the hydraulic-flushing effect is evaluated in a traditional way, by determining the desorption volume, moisture content, gas drainage rate and other conventional indices. To verify the rationality and feasibility of the multielectrode resistivity method in the evaluation of coal-seam hydraulic flushing and to research the spatio-temporal evolution of apparent resistivity during hydraulic flushing, a field test was conducted in 17# coal seam at Nuodong Mine, Guizhou. During hydraulic flushing, four stages were defined according to the variation in coal rock resistivity with time, namely, the preparation stage, the sharply decreasing stage, the rapidly increasing stage and the steady stage. The apparent resistivity of the coal rock mass is affected mainly by its own degree of fragmentation and flushing volume. A more serious rupture and a greater flushing volume yield a smaller apparent resistivity during the sharply decreasing stage and a higher resistivity during the stable stage. After three months of gas predrainage, the residual gas content and the gas pressure at different points in the expected affected area decrease below the critical value. Changes in the residual gas content and gas pressure at these points are consistent with the apparent resistivity, which validates the rationality and feasibility of the multielectrode resistivity method in evaluating coal-seam hydraulic flushing.

Coal dust explosion tests were performed in a 20-L spherical vessel and the post-explosion dust samples were collected for analysis. Various characteristic parameters of each explosion trial were r...

Fabricating sulfur host for the cathode with strong confinement effect and high dispersion of sulfur is vitally important to the development of high-performance lithium sulfur batteries. Benefiting from their unique and tunable structure, good conductivity and chemical inertness, hollow porous carbon materials has been considered as a promising candidate. Herein, precisely designed waxberry-like hierarchical hollow carbon spheres (h-CNS) have been synthesized as the sulfur micro-containers for lithium sulfur batteries. The prepared h-CNS/S electrode shows a good rate capability of 1311 mAh g-1at 0.1 C and 962 mAh g-1at 1 C. In addition, the h-CNS/S electrode also shows satisfactory long cycle performance with 622 mAh g-1at 0.5 C and 400 mAh g-1at 4 C over 600 cycles. The desirable performance can be attributed to the wedge-shape micro-containers which improve the high dispersion of sulfur inside the channels and inhibit the loss of intermediate polysulfide. Moreover, the unique structure can also enhance the transfer of both lithium ions and electrons which benefits to the rate capability of the lithium sulfur batteries.

The temporal evolution of aerosolized SiO 2 nanoparticles (NPs) released into an environmental test chamber has been investigated to interrogate the effect of relative humidity (RH) on the deposition and coagulation of the nanoparticles. The size-resolved deposition rate and Brownian coagulation coefficient for the particles at RH of ~ 10%, 27%, 40%, 54%, and 64% are estimated. The results show that the effect of RH on the deposition rate is size-dependent; for particle diameter (Dp) 70 nm, it grows as the RH rises. Generally, both low and high RH tends to enhance the deposition rate, and the minimum rate appears at moderate RH (~ 54%). Electrostatic repulsion is probable for the inter-particles interaction at the low RH while the surface roughness due to water molecular adsorption is a main reason for the particle-wall interaction at higher RH. The increasing coagulation coefficient at high humidity correlates to the strong inter-particle adhesion, which may be caused by the water molecular adsorption on the hydrophilic surfaces of the SiO 2 NPs due to the formation of nanometer-thick water film. This study suggests that air humidity plays unignorable roles in particle deposition and coagulation.

Thermodynamic and kinetic signatures are pivotal information for revealing the binding mechanisms of biomolecules, and they play an indispensable role in drug discovery and optimization. While noncalorimetric methods measure only a part of these signatures, isothermal titration calorimetry (ITC) is considered to have the potential to acquire full signatures in an experiment. However, kinetic parameters are generally difficult to extract from ITC curves, as they are inevitably affected by the instrument-response function and the collateral heat of associated process during titrations. Thus, we herein report the development and validation of a full-curve-fitting method to resolve thermal power curves and to maximize the signal extraction using ITC. This method is then employed to quantify the dilution of an aqueous n-propanol solution and examine the inhibition of carbonic anhydrase by 4-carboxybenzenesulfonamide using a commercial instrument with a long apparent response time of ∼13 s.

Based on poroelasticity theory and diffusion-seepage mechanism, the dual porosity and permeability evolution model was established by considering fracture gas pressure and pore gas pressure, respectively. By the solid and PDE modules of COMSOL Multiphysics, the protective seam mining was simulated on the base of the effective coupling of stress and gas fields. The results showed that with the mining of the protective layer, stress relief region (SRR) and stress concentration region (SCR) are formed in the protective seam, which correspond to the gas releasing region (GRR) and gas accumulative region (GAR), respectively, in the protected seam. The porosity and permeability increase in the SRR, whereas they decrease in the SCR. It is notable that the porosity cannot be restored to the original level due to the irreversibility of internal damage in coal mass. With further mining, the surrounding rock is tensioned to form the damage region, in which tensile fractures are formed, which eventually expand and connect with each other. When the destruction area gradually enlarges to link up the protected coal seam and the gob of the protective layer, the methane accumulated in the protected coal seam flows into the gob. The evolution of stress, porosity, and gas pressure is closely related. The variation of stress will cause change in porosity, which influences gas pressure, whereas the desorption of methane affects the stress of coal, all of which together form the coupling relation. This study is helpful to reveal the coupling mechanism of coalbed stress and methane, understand the dynamic porosity and permeability evolution, and learn tensile damage development.

Reference materials (RM)-assisted Rayleigh-Gans-Debye approximation (rm-RGDA) has been developed and used to in situ determine the size and thickness of the adlayer on the particles in solution. The particle size determined by rm-RGDA is quite close to that measured by electron microscopy but significantly smaller than that measured by DLS. The BSA adlayer absorbed on PS50, PS100 and SiO2 NPs is 3.3, 0.9 and 1.2 nm, respectively, and close to those observed by SEM, which is 4.6, 1.3 and 3.8 nm, respectively. The FTIR analysis results show that the BSA absorbed on larger particles or hydroxyl-abundant surface, e.g. PS100 and SiO2 NPs can lose its secondary structure, e.g. α-helix, to a great extent and that absorbed on a more curve surface, e.g. smaller PS50 particles can largely preserve its secondary structure as its free state. The measurement results show the curvature of the NPs is closely related to the structure change of the adsorbed protein. This method provide a facile and new approach to measure the size and its adlayer change of the hybrid and core-shell structured nanoparticles in a wide range of wavelength.SIGNIFICANCEQuantitative study on the adsorption of the protein on colloidal nanoparticles is an important approach to understand the biophysical effect, compared with other ex situ methods such as TEM and SEM, where the specimen are undergone pre-processing and no longer the original state in measurement. It is, therefore, a big challenge. In order to cope with this challenge, UV-vis based RGDA has been developed and applied to in situ measure the size of the dispersed colloidal nanoparticles and their protein adlayer thickness, where the protein adlayer thickness on the colloidal nanoparticles can be easily determined. We believe this method provide a facile and sensitive way to in situ measure the dimension change of hybrid colloidal nanoparticles.

The role of the C?OH group in citric acid (CA) in the molecular coordination with Fe3O4 nanoparticles (NPs) has been elusive for a long time. In this study, attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectral deconvolution and thermogravimetric analysis (TGA) have been used to quantitatively clarify its significance in CA adsorption and its corresponding conformation. The experimental results show that the coordination and the corresponding conformation are exclusively determined by COOH not C?OH at pH 3, where its adsorption behavior conforms to the Brunauer?Emmett?Teller (BET) multilayer model with a maximal monolayer coordination number of 2.1/nm2. However, C?OH is involved in the coordination at pH 10, and CA conforms to the Langmuir monolayer model with 1.4/nm2 as its maximal monolayer coordination number, which is more stable than the COOH-only coordination. Especially, the conformational transformation is observed for the first time at pH 3, where the CA molecules adjust their conformation upon elution to maximize the utilization of the available binding sites on Fe3O4 NPs. This finding deepens the understanding on the fundamental mechanism for the interaction between the C?OH and COOH groups containing the organic ligand and metal oxide.

The role of the C?OH group in citric acid (CA) in the molecular coordination with Fe

In order to study the mechanics and acoustic emission (AE) characteristics of fractured rock under water-rock interaction, dried and saturated sandstone samples with prefabricated double parallel cracks were prepared. Then, uniaxial compression experiments were performed to obtain their AE signals and crack propagation images. The results show that water reduces the strength and fracture toughness of fractured sandstone and enhances plasticity. After saturation, the samples start to crack earlier, the cracks grow slowly, the failure mode is transformed from shear failure along the prefabricated cracks to combined shear and tensile failure, more secondary cracks are produced. The saturated samples release less elastic energy and weaker AE signals in the whole failure process. However, their AE precursor information is more obvious and advanced, and their AE sources are more widely distributed. Compared with dry specimens, the AE frequencies of saturated specimens in the early stage of loading are distributed in a lower frequency domain. Besides, the saturated samples release less complex AE signals which are dominated by small-scale signals with weaker multi-fractal characteristics. After discussion and analysis, it is pointed out that this may be because water makes rock prone to inter-granular fracture rather than trans-granular fracture. The water lubrication also may reduce the amplitude of middle-frequency band signals produced by the friction on the fracture surface. Multi-fractal parameters can provide more abundant precursory information for rock fracture. This is of great significance to the stability of water-bearing fractured rock mass and its monitoring, and is conducive to the safe exploitation of deep energy.

For bimetallic nanoparticles (NPs), the degree of alloying is beginning to be recognized as a significant factor affecting the NP properties. Here, we report an alloyed crystalline Au-Ag hollow nanostructure that exhibits a high catalytic performance, as well as structural and chemical stability. The Au-Ag alloyed hollow and porous nanoshell structures (HPNSs) with different morphologies and subnanoscale crystalline structures were synthesized by adjusting the size of the sacrificial Ag NPs via a galvanic replacement reaction. The catalytic activities of the nanomaterials were evaluated by the model reaction of the catalytic reduction of p-nitrophenol by NaBH4 to p-aminophenol. The experimental results show that the subnanoscale crystalline structure of the Au-Ag bimetallic HPNSs has much greater significance than the apparent morphology does in determining the catalytic ability of the nanostructures. The Au-Ag alloyed HPNSs with better surface crystalline alloying microstructures and open morphologies were found to exhibit much higher catalytic reaction rates and better cyclic usage efficiencies, probably because of the better dispersion of active Au atoms within these materials. These galvanic replacement-synthesized alloyed Au-Ag HPNSs, fabricated by a facile method that avoids Ag degradation, have potential applications in catalysis, nanomedicine (especially in drug/gene delivery and cancer theranostics), and biosensing.

Current coal seams in China are characterized by great depth, low permeability, and strong adsorption features, and thus, the extraction of methane is relatively difficult and gas disaster remains serious. To overcome this limitation, the hydraulic flushing and hydraulic slotting are adopted to improve the permeability of coal seams. A 2D model of gas seepage was established by using the solid mechanics and darcy module in Comsol Multiphysics, version 4.3b. The factors influencing pressure relief, such as the radius of borehole after hydraulic flushing, the initial gas pressure, and the permeability of coal seam, were studied. The coupling effects of these three factors on the effective influence radius were studied through the response surface methodology, and a quadratic polynomial equation between effective influence radius and three factors was derived. The results showed that Gas pressure distribution (e.g. gas full emission region, gas pressure transition region and original gas region) near the borehole, corresponded well with stress distribution (stress relief zone, stress concentrating range and original stress zone). The plastic zone formed around the borehole leaded to stress reduction, and the increasing porosity and permeability resulted in pressure decline. The effective influence radius increased with the borehole radius and the initial permeability, but decreased with original gas pressure. Besides, it was found that an increase in one factor would restrict the role of other two factors on the effective influence radius. This study is helpful to choose the most suitable parameters to achieve high extraction efficiency and lower gas content/pressure.

Continuous efforts have been devoted to improve the accuracy and reliability of isothermal titration calorimetry (ITC) in terms of instrumental design, modeling and data processing. Among various factors, background noise, proportional error and injection volume error lead to heteroscedasticity (non-constant variance) of the titration heat. The variance function method provides an efficient way to estimate the non-constant variance and weight of the titration heat. Following this approach, in this work, the heat residual recorded by calorimeter model of Nano ITC Standard Volume was examined in detail. Based on the CaCl2-EDTA saturated titration and water blank titration, 9 heat variances, each from 60 injections, have been analyzed, which provide reliable information about the variance function. The major statistical errors for general titrations were estimated and the non-constant variance distribution of typical titration (BaCl2 to 18-Crown-6) was successfully predicted.

In order to study the effect of water on the electromagnetic radiation (EMR) signals released during rock deformation and fracturing, uniaxial compression experiments were performed on sandstone samples with different water contents. During the experiments, the EMR signals were acquired. Furthermore, the time-frequency characteristics of the signals were analyzed, and their generation mechanism and the effect of water were discussed in depth. The results show that the EMR energy released decreases gradually with the increase of water content, and the EMR energy and water content can be linked by a binomial equation. For sandstone with higher water content, the precursor characteristics of EMR released in the fracturing process are more obvious. With the increase of water content, the proportion of signals in the low frequency band grows gradually, while that of signals in high frequency band falls gradually. Water reduces the macroscopic mechanical strength and fracture mechanical characteristics of sandstone, which weakens the EMR signals produced by piezoelectric effect and charge separation. Besides, with respect to the microscopic fracturing mode, the sandstone with higher water content is more likely to undergo inter-granular fracturing, which may be an important microscopic reason for the weakening of EMR of water-bearing sandstone. An EMR-based damage evolution model of water-bearing sandstone was preliminarily established, and the model helps to calculate the stress state of water-bearing rock.

The coordination of valeric acid (VA), glutaric acid (GA), and tricarballylic acid (TA) with Fe-OH on the Fe

The acoustic emission (AE) and ultrasonic (UT) simultaneous monitoring program is designed using concrete samples under step loading. The time-varying response characteristics of AE-UT are studied and the cross-correlation analysis between AE-UT parameters is obtained. Moreover, the joint response of UT-AE spatial distribution field is analyzed, and an AE-UT joint monitoring method to detect early-warning signals of a rockburst disaster in a coal seam is proposed. The results show the following. (1) During the loading process, the AE pulses/energy and UT attenuation coefficient first slowly decrease and then increase steadily and finally rapidly increase, while the UT velocity shows a trend of first gradually increasing and then slowly decreasing and finally a sharp decline. (2) AE pulses and energy are significantly or highly correlated with the UT velocity and attenuation coefficient. The AE energy and UT attenuation coefficient can better characterize the damage evolution of concrete under step loading. (3) The UT field evolves ahead of the rupture on the surface, and the long/narrow strip distribution region of UT parameters is consistent with the future failure zone; meanwhile, the AE events can visually reflect the evolution path of internal damage as well as the dynamic migration mechanism of UT field.