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The analyses of the LHCb data on $X(6900)$ found in di-$J/\psi$ and $J/\psi \psi(3686)$ systems are performed using a momentum-dependent {Flatt\'{e}}-like parameterization. The use of the pole counting rule and spectral density function sum rule give consistent conclusions that $X(6900)$ may not be a molecule of $J/\psi \psi(3686)$. Nevertheless it is still possible that $X(6900)$ be a molecule of higher states, such as $J/\psi\psi(3770)$, $\chi_{c0}\chi_{c2}$, etc., Comment: 7pages with 9 figures

Distinguished by the coupled catalysis-facilitated high turnover and admirable specificity, enzyme cascades have sparked tremendous attention in bioanalysis. However, three-enzyme cascade-based versatile platforms have rarely been explored without resorting to tedious immobilization procedures. Herein, we have demonstrated that formamide-converted transition metal-nitrogen-carbon (f-MNC, M = Fe, Cu, Mn, Co, Zn) with a high loading of atomically dispersed active sites possesses intrinsic peroxidase-mimetic activity following the activity order of f-FeNCf-CuNCf-MnNCf-CoNCf-ZnNC. Ulteriorly, benefitting from the greatest catalytic performance and explicit catalytic mechanism of f-FeNC, versatile enzyme cascade-based colorimetric bioassays for ultrasensitive detection of diabetes-related glucose and α-glucosidase (α-Glu) have been unprecedentedly devised using f-FeNC-triggered chromogenic reaction of 3,3',5,5'-tetramethylbenzidine as an amplifier. Notably, several types of α-Glu substrates can be effectively utilized in this three-enzyme cascade-based α-Glu assay, and it can be further employed for screening α-Glu inhibitors that are used as antidiabetic and antiviral drugs. These versatile assays can also be extended to detect other H

Force-chain is the main load-bearing structure in the granular materials. The study of force chains and particle breakage is of great significance to understand the mechanical properties of the granular materials. At present, the internal relationship between the force chains and particle breakage is still unclear. It also has no idea about the crushing mode of the particle system with complex gradation and stress path. Therefore, in the present paper, the continuous-discontinuous numerical method (Numerical Manifold Method, NMM) is utilized to simulate the process of the force chains generation and particle breakage in granular material and to explore their internal connection mechanism. The simulation results show that the particle breakage is directly related to the force-chain network, and the particle breakage morphology is basically consistent with the direction of the force-chain network in the granular system. Small particles are broken firstly, producing large displacement to fill the voids in the system. Although the larger particles can also be broken, it is difficult to produce large displacement due to the influence of coordination number among particles. Furthermore, particle breakage can reduce the strength of the force-chain, resulting in that the larger particles in the force-chain will be broken slightly or not.

Rock is generally regarded as a heterogeneous and anisotropic material containing massive initial defects, such as cracks, joints, and porosities. In the present work, based on the maximum tensile stress and Mohr–Coulomb criteria, the fracturing modeling algorithm implemented into the numerical manifold method (NMM) is perfected and applied to a comprehensive simulation study of the fracturing of rock specimens. Disc and semi-disc specimens containing a single pre-existing crack, along with rectangular specimens containing two parallel pre-existing cracks, are simulated, respectively, to verify the fracturing modeling algorithm in terms of crack initiation, propagation, interaction, and coalescence. On this basis, four rectangular specimens containing multiple randomly distributing cracks are also simulated and the effective mechanical response of the specimen is investigated. The simulation of disc and semi-disc indicates that the crack initiation, propagation, and final crack path are all in great agreement with the experimental results. The simulation of rectangular specimens with two parallel pre-existing cracks shows the crack interaction and coalescence of the crack pairs. The results are also in good agreement with the experimental and theoretical results. For the simulation of complicated model with multiple cracks, results indicate that the increase in the crack density leads to a dramatic decrease in the effective elastic modulus and compressive strength as the evolution of pre-existing cracks. The NMM enriched with the fracturing modeling algorithm can be applied to solve more rock fracturing problems with diverse type and large number of initial defects.

In this work, a novel convenient colorimetric method for sensitive detection of thiocyanate (SCN−) has been developed based on its suppression of the oxidase-like activity of palladium square nanoplates on reduced graphene oxide (Pd SP@rGO). SCN− can be adsorbed onto the surface of Pd SP@rGO via binding with Pd atoms and blocks the active sites that mimic oxidase, thus inhibiting the corresponding chromogenic reaction of 3,3′,5,5′-tetramethylbenzidine, which has been comprehensively revealed by the UV-vis spectra and X-ray photoelectron spectra. The color fading exhibits SCN− concentration-dependent behavior and can be easily recorded by either UV-vis spectroscopy or naked-eye observation. Therefore, both quantitative detection via measurement of the decrease in absorbance and visual detection of SCN− can be achieved. Owing to the intrinsic amplification of signals by the oxidase-like activity of Pd SP@rGO without resorting to unstable and destructive H2O2, this assay is straightforward, robust and sensitive enough for the detection of SCN− in real samples. Furthermore, an “INH” logic gate is rationally constructed based on the proposed colorimetric SCN− sensor.

As energetic composite materials, polymer bonded explosives (PBX) are composed of highly filled explosive crystals and a small of polymer binder. Accidental explosion could occur under low velocity impact. The ignition mechanism has drawn great attention to scientists and engineers. Hotspot is considered to induce the occurrence of ignition. Our works focus on the relation between the microcrack evolution and hotspot formation. The deformation, damage and failure behavior of PBX was investigated by split Hopkinson pressure bar, gas gun impact and penetration. In these dynamic loading experiments, the microstructure of the recovered specimens was analyzed by scanning electron microscope. It reveals that the cracking along the interface between the explosive crystal and the polymer binder under the tension, while the intergranular fracture is the main mode under the compression. The numerical manifold method was developed to simulate the tension and compression behavior. The effect of the initial defect, the strain rate and temperature on the tension and compression behavior was analyzed. The fracture modes of the tension and compression match the dynamic experiments above well. The low impact ignition analysis was conducted by means of Steven impact test. The specimen size effect on the ignition was mainly focused. The ignition observation and ignition delay time were measured. Also, the ignition velocity and reaction level were discussed. In addition, based on Visco-SCRAM model, a mechanical-thermal-chemical coupling model was developed to understand the ignition behavior in Steven impact test. The effect of the impact velocity on the ignition was analyzed. The mechanism of the size effect on ignition was discussed. Different projectile shapes were designed to act on the specimen. The difference of the ignition among these projectiles was compared. Further, the model was applied to simulate the multi impact corresponding to the real application scenarios. Moreover, in order to refine the microcrack evolution, the tension-compression asymmetrical microcrack evolution was proposed. The stochastic distribution of the microcrack length and density produced the ignition uncertainty, and further based on the Monte Carlo method, the ignition probability was quantified. These simulations matched the experimental results well.

Discontinuous deformation analysis (DDA) computes the mechanical behaviours of discrete deformable-block systems. It also has been used to simulate continuous rock fracturing, e.g., through the sub-block approach. In the present study, the sub-block DDA method is first verified in simulations of continua. The influences of the contact penalty spring stiffness and mesh size on the stress and strain calculations are investigated. Thereafter, the fracturing modelling algorithm of the sub-block DDA is improved, which determines the tensile or shear fracturing failure along artificial joints based on the stress state of adjacent sub-blocks according to the maximum tensile stress criterion and the Mohr–Coulomb criterion, respectively. The tensile, shear, mixed-mode, as well as dynamic fracturing failures of rock samples are simulated, and the results are calibrated theoretically or experimentally. Compared with former sub-block DDA fracturing modelling algorithms which determine the fracturing failure along artificial joints based on the contact stresses between sub-blocks, the improved algorithm has better accuracy in terms of the failure strength, and it significantly reduces the influence of the distribution of the pre-set artificial joints on the failure strength and fracturing route simulation results. This work makes DDA a better candidate for use in rock fracturing problem simulations.

The polymer-bonded explosive (PBX) is a kind of multi-phase composite consisting of the polymeric binder and embedded energetic particles, in which the particle volume fraction (PVF) is often highe...

Polymer bonded explosive (PBX) is a particle-matix composite consisting of explosive particles, polymer matrix/binder, and the interface between the particles and the binder, and the particle volume fraction (PVF) in the PBX is extremely high. To simulate the meso-scale deformation and damage behaviors of PBX with the numerical manifold method (NMM), a bilinear cohesive contact relationship (BCCR) model with three parameters is incorporated in the NMM to describe the particle-binder interface, a visco-elastic constitutive model of prony series with 22 parameters is incorporated in the NMM to describe the polymer binder, and a fracturing algorithm based on the maximum tensile stress criterion and the Mohr–Coulomb criterion is employed to describe the fracturing failures of the particles as well as the binder. The PBX meso-scale deformation and damage process of microcrack initiation, crack propagation and formation of crack bands under tensile or compressive conditions are studied through NMM simulations, and the influenes of the PVF and the explosive particle geometrical distribution (PGD) on PBX mechanical performaces are specially investigated. This work enables and proves the NMM to be an promissing roubust numerical tool for further simulation studies of the meso-scale mechanical performances of PBX, as well as other particle-fillled polymer composites.

Dynamic cracking behavior of energetic composite materials (ECMs) is very difficult to be modelled due to the complex microcrack evolution. The microcrack evolution in highly particle-filled composite materials presents asymmetrical characteristics under tension–compression. In this paper, a dynamic mesoscale viscoelastic model taking into account the microcrack growth is developed to simulate the center splitting phenomenon of the Octahydro-1,3,5,7-Tetranitro-Tetrazocine-based ECM Brazilian disc under dynamic loadings by means of the Hopkinson bar test. The microcrack evolution modeling fully considers cracking nucleation, growth and coalescence. The Mohr-Coulomb failure criterion is used to drive the crack propagation. The dynamic cracking formation in the test is captured well. The details of the cracking are analyzed for different loading conditions. The cracking initiation orientation is modelled with different precrack conditions. In addition, the effect of the failure criterion on the dynamic cracking condition is determined. Further, the heterogeneous failure surfaces are considered and compared with the unique failure surface condition.

Particulate-filled composite (PFC) is a kind of mixed multi-phase material with the grains highly embedded in the binders with ratio higher than 90%. Its good mixture capacity with the binder, in particulate or fibre form, leads to composite materials with intermediate properties that result from the combined action of the constituents. Due to the complexity of PFC meso-scopic composition and loading levels, it is difficult to reveal the deformation and damage mechanism of composites by traditional phenomenological macro-scale methods. In the present work, based on the PFC meso-structures with highly-filled grains, the numerical manifold method is utilized to simulate the meso-scale mechanical response of PFC at different loading levels. The effects of strain rates and temperatures on the meso damage morphology of PFC are studied. The damage evolution laws caused by interfacial debonding and micro-cracks in the meso structure are analyzed. Based on their isotropic assumption, the macroscopic equivalent damage evolution equations caused by these meso-scale damages are derived, respectively. The effects of loading levels on the mechanical characteristic parameters (such as modulus, failure strength, ultimate strain, etc.) are also discussed quantitatively. The specific mathematical expressions of the strain rate and temperature dependent properties under uniaxial tension/compression are statistically obtained. Two categories of constitutive models of coupling damage evolution equation with Johnson-cook and generalized Maxwell model are proposed to describe the macroscopic equivalent mechanical behavior of PFC.