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Many researches have shown that nanotwinned structure and graphene reinforcing phase can improve the mechanical properties of aluminum (Al) metal, but the synergistic effect of the two on nanoindentation mechanical response of Al matrix composites is rarely reported. In this research, based on molecular dynamics simulations, the nanoindentation mechanical properties and microscopic deformation mechanisms of graphene/nanotwinned Al matrix composites are studied. The effect of the inclination angle and spacing of the twin boundaries (TBs), the insertion position of the graphene sheet, the graphene coating and the layer number of the graphene sheet on the nanoindentation mechanical properties of the Al matrix composites is analyzed. The nanoindentation mechanical properties of nanotwinned Al strongly depend on the inclination angle of TBs, and the dislocation slip modes mainly includes three types: hard mode I (dislocation pile-up penetration mode), soft mode I (partial dislocation parallel twin boundary slip mode) and hard mode II (dislocation limited slip mode). Moreover, as the twin boundary spacing increases, the dislocation slip mode starts to weaken until the nanoindentation mechanical properties are insensitive to the twin inclination orientation. The insertion of the graphene sheet weakens the indentation mechanical properties of the nanotwinned Al matrix composite, which is attributed to the interaction of the graphene with the dislocations and the subsequent absorption of part of them. The weakening effect depends on the distance between the graphene/Al interface and the plastic zone. What's more, graphene coating can improve the indentation mechanical properties of composites. In addition to the load bearing effect of graphene in the elastic stage, this strengthening effect is also attributed to the combined action of graphene and TBs in the plastic stage, which makes the dense dislocation network widely distributed around the indentation of graphene coating and induces the interfacial strain hardening. [ABSTRACT FROM AUTHOR]

[Display omitted] • Adhesive forces of a single anisole on G-OH/Gr surface are got via AFM experiments. • Anisole exhibits two types of adhesive forces on G-OH surface. • Hydroxyl group has significant effect on the adhesive force of G-OH to anisole. • Conformational changes of anisole cause two peaks of its force-height curve to G-OH. Measuring and understanding interaction forces between hydroxylated graphene (G-OH) and aromatic compounds is significant for the applications of composites based on G-OH, such as 3D graphene derivatives preparation and wastewater treatment. In this research, the adsorption/separation mechanical behavior of anisole on graphene and G-OH surfaces was investigated by atomic force microscopy (AFM) experiments and molecular dynamics (MD) simulations. The adsorption and separation curves of anisole on graphene and G-OH surfaces were obtained by experiments, and the adhesive forces of a single anisole were achieved by the Poisson statistics method. It is found that there are two types of adhesive forces between anisole and G-OH. For graphene and anisole, two extreme values are got by the adsorption and separation processes, and the adhesive force obtained by the separation process is approximately equal to one type of adhesive force between anisole and G-OH. Furthermore, MD simulation results reveal that the maximum adhesive force of anisole on the G-OH surface depends on its position relative to the hydroxyl group, and anisole has a greater affinity near the hydroxyl group. The position and planar angle of the anisole conformations cause the difference in adhesive forces. [ABSTRACT FROM AUTHOR]

In drug delivery systems, graphene materials are promising drug carriers. Drug molecules are loaded on graphene through π-π interaction between graphene and benzene ring structure, which is widely found in organic drug molecules. Then the drug molecules are released under different conditions, such as different environmental pH, at lesion site. In the application, the adsorption and desorption between benzene ring structure in drug molecules and graphene play a key role. Herein, an experimental method for measuring the adhesion force between a single phenyl and graphene is proposed, and the adsorption and desorption mechanical properties of a benzene ring structure on graphene surface at different environmental pH are firstly measured. The experimental results show that the adhesion force decreases with the increase of environmental pH. Moreover, molecular dynamics simulations show that the influence of pH on adhesion force is mainly realized by changing the electrostatic potential distribution on graphene surface, and the interaction force between a single benzene and graphene changes from attractive to repulsive with the increase of environmental alkalinity. In addition, a molecular dynamics model for the dynamic adsorption and desorption capacities of benzene molecules on graphene surface at different quantity of ions is established. Benzene molecules can achieve full adsorption on the surface of graphene when there are 10 and 20 hydrogen ions. And benzene molecules can achieve full desorption on the surface of graphene when there are 10 and 20 hydroxide ions. [Display omitted] [ABSTRACT FROM AUTHOR]

A series of three-dimensional molecular dynamics (MD) simulations was performed to investigate the effect of temperature on the nanoscale deformation behaviour and mechanical properties of c -plane monocrystalline gallium nitride (GaN) under nanoindentation. Simulation results showed that the atomic displacement and strain increased with increasing temperature. Thus, the nucleation and propagation of dislocations in the main slip systems were promoted to intensify the plastic deformation of GaN crystal. Increasing the temperature also contributed to the increase in local phase transition from the wurtzite crystal structure (B4-GaN) to the zinc-blende crystal structure (B3-GaN) and a very evident amorphization of GaN in the indentation zone. Based on the analysis of the load-depth curves, it was found that both the hardness and Young's modulus decreased as the temperature increased. This work can enrich the atomic-level understanding of the effect of temperature on the mechanical response of monocrystalline GaN when subjected to the external loads. [ABSTRACT FROM AUTHOR]

We simulate dynamical mechanical spectroscopy in a Cu 64 Zr 36 bulk metallic glass using non-equilibrium molecular dynamics. Applying several loading conditions (constant volume, longitudinal, uniaxial and isostatic), we find that different elastic moduli have very contrasted dynamical properties but satisfy the dynamic correspondence principle, which states that the relations between static moduli can be extended to dynamical moduli, both below and above the glass transition temperature. In particular, we determine the debated dynamic Poisson's ratio from three different but consistent expressions. Finally, we trace the origin of dissipation down to regions of low stability devoid of icosahedral clusters. Unlabelled Image [ABSTRACT FROM AUTHOR]

The superb mechanical properties make graphene an ideal candidate material for impact protection. Combining molecular dynamics simulations and theoretical analyses, the deformation and failure modes, energy absorption of single-layer graphene under ballistic impact are investigated. According to numerical and theoretical results, the expression for residual velocity of projectile after impact is given. The dependence of deformation and failure modes, energy absorption mechanisms, specific penetration energy (SPE) on impact velocity is analyzed. The results show that during low-velocity impact, there are conical deformation region (CDR), star-like crack and monoatomic carbon chain in graphene. Energy absorption mechanisms of graphene are mainly local deformation and fracture. With increasing impact velocity, the size of CDR decreases. The star-like crack gradually transforms into circular hole. When impact velocity is high enough, carbon atoms within projectile projection area in graphene will be ejected in the form of debris. The kinetic energy (KE) loss of projectile is converted into KE of debris carbon atoms and fracture energy of carbon bonds. Besides, it is also found that SPE (dominant factors are deformation of conical region and KE increments) exhibits a decreasing–increasing trend with increasing impact velocity. When impact velocity is the same, SPE decreases with increasing projectile diameter. [Display omitted] • Energy absorption of graphene under ballistic impact is studied by MD simulations. • The expression for residual velocity of rigid projectile after impact is given. • The dependence of deformation and failure modes on impact velocity is discussed. • Energy absorption mechanism of graphene during impact process is analyzed. • The effect of impact velocity on specific penetration energy is studied. [ABSTRACT FROM AUTHOR]

In field of drug delivery, graphene is a potential material as drug carrier due to its large specific surface area and excellent chemical stability. Many kinds of drug molecules can be adsorbed on graphene surface through single or multiple benzene ring structures in drug molecules. Graphene loaded with drug molecules needs to be transported to the lesion site through blood. The content of water molecules in blood accounts for 92%. Therefore, the influence of water molecule on adsorption performance cannot be ignored. Here, the influence and mechanism of water molecule on the adsorption properties between benzene molecule and graphene is studied. The adsorption models of benzene molecule on graphene surface in vacuum and water environments are established, respectively. The adhesion energy, adhesion force and stable adsorption position of benzene molecule in two environments are analyzed by molecular dynamics simulation and potential function theory. Moreover, a model of preadsorption of a single water molecule on graphene surface is further presented, which explains the reason of the difference in adsorption performance in vacuum and water environment from the perspective of energy. The preadsorption of water molecule on graphene surface promotes the adsorption of benzene molecule. [Display omitted] [ABSTRACT FROM AUTHOR]

Temperature-dependent material attrition and subsurface lattice damage of single-crystal AlN at various scratching depths/forces are investigated at atomic level using molecular dynamics simulation. An ultimate removal precision of depth down to monolayer of AlN is achieved based on the present temperature-dependent critical conditions. The number of worn atoms, positively influenced by temperature due to the reduction of hardness, increases exponentially with increasing normal force in the plastic domain. Archard-type wear coefficient K values calculated at different temperatures increase linearly with normal force, and the slope is independent of temperature. Independently of load and temperature, a wear coefficient normalized with the tangential contact area, K / A tang , is developed to interpret the removal efficiency of AlN substrate with diamond abrasive. • Temperature-dependent plastic removal of AlN was elucidated at atomic level via MD simulation. • Increasing temperature can promote wear of GaN primarily due to the reduction of hardness. • Atomic layer removal of AlN is realized over a wide temperature range. • Temperature-independent wear coefficient increases linearly with normal load. • A normalized wear coefficient, K / A tang , is developed to interpret the removal efficiency of AlN with diamond abrasive. [ABSTRACT FROM AUTHOR]

Many studies have shown that both the nanotwinned structure and the graphene reinforcing phase can improve the mechanical properties of aluminum, but the synergistic effect of the two on the strengthening and toughening mechanisms of aluminum matrix composites has rarely been reported. In this work, the mechanical properties and microscopic deformation mechanisms of graphene/nanotwinned aluminum matrix composites under uniaxial tensile load are studied by molecular dynamics simulations. The effects of the distribution patterns of graphene and twin boundaries (TBs), their angles and the number of graphene layers on the mechanical behaviors of graphene/nanotwinned aluminum matrix composites are analyzed. It is found that the synergistic effect of TBs and graphene results in secondary reinforcement of aluminum matrix composites in the plastic stage, resulting in enhanced strength and toughness. Moreover, the elastic modulus, strength and toughness of graphene/nanotwinned aluminum matrix composites increase linearly with the number of graphene layers. By analyzing the microscopic deformation and dislocation evolution of aluminum matrix composites, the mechanisms of dislocation derivation and propagation induced by graphene and TBs are explored. In addition, it is found that there is a competition between graphene and TBs for the dislocation evolution, and the graphene can weaken the dislocation blocking effect of TBs. Finally, it is proved that the angle between graphene and TBs will weaken the mechanical properties of the composites. The effect of the TB angle on the mechanical properties of graphene/nanotwinned aluminum matrix composites is discussed in three cases, depending on the stress-strain curve and the microstructure deformation mechanism. • The effect of graphene and TBs on mechanical properties of Al-matrix is studied. • The influence of distribution patterns and layer number of graphene is analyzed. • The effect of the inclination angle of TBs and graphene is considered. • The mechanisms of dislocation derivation and propagation is explored. [ABSTRACT FROM AUTHOR]

The mechanism of sputtering due to cluster impacting which has been widely studied is an important but unsolved problem. In present research, we discuss the effect of the landing point on the sputtering with the method of molecular dynamics. The results show that the landing points play significant roles on sputter yield when the temperature of target is low. Specific landing points can cause particular sputtering patterns which lead to different sputtering yield and moving directions of sputtered atoms. The mechanism of this phenomenon is that specific landing keeps symmetries and anisotropies of target lattice, which influence the sputtering yield. [ABSTRACT FROM AUTHOR]

Molecular dynamics (MD) simulations have been performed to investigate the diffusion properties of hydrogen (H) atoms in body-center-cubic (bcc) iron (Fe) with point defects, i.e., vacancies (Vs) and self-interstitial atoms (SIAs). Firstly, the binding energies of a H atom to a H/SIA-H cluster have been calculated by molecular statics simulations. The results show that single-H diffusion should be the major diffusion mechanism in perfect bcc Fe and bcc Fe with SIAs, but for bcc Fe with Vs, results from literatures show that multi-H diffusion should be taken into account. Further, the mean squared displacements method has been employed to determine the diffusivities and diffusion energy barriers of single-H at different temperatures in perfect bcc Fe. The diffusion energy barrier varies with the temperature. Furthermore, the H diffusion properties with different point defect concentrations have also been demonstrated, which showed that diffusivities reduce as the point defect concentration increases and the influence of point defects reduces as the temperature increases. Especially, SIAs exhibit negligible effect when the temperature is higher than 600 K. [ABSTRACT FROM AUTHOR]

Dust velocity in fusion devices covers a wide range (several hundreds of m/s to over 10 km/s), which can cause various interactions between energetic dust grains and wall materials. Dust grain with low energy can influence the wall properties by deposition. Intense dust-wall interactions can cause serious wall damage such as sputtering, degradation, deformation and so on. As beryllium and tungsten are the material of the first wall and divertor, respectively, systematically molecular dynamics simulations have been performed to study the interactions between beryllium/tungsten dust and the beryllium/tungsten wall in the present study. A wide range of dust velocity has been considered to cover the velocity from experiments. Our result shows that the influences of dust on the wall are greatly affected by the impact velocity of dust grains and the properties of the wall material. A detailed analysis shows that the dust-wall interaction can be divided into four levels and an analytical model has been developed to explain the mechanism. Character velocities that separate the interaction levels are also provided by the model. The comparison between the MD result and the model shows a good agreement. Our result is helpful for the understanding of the mechanisms and the prediction of dust-wall interactions. [ABSTRACT FROM AUTHOR]

The interactions between dust and plasma-facing material (PFM) relate to the lifetime of PFM and impurity production. Series results have been obtained theoretically and experimentally but more detailed studies are needed. In present research, we investigate the evolution of kinetic, potential and total energy of plasma-facing material (PFM) in order to understand the dust/PFM interaction process. Three typical impacting energy are selected, i.e., 1, 10 and 100 keV/dust for low-, high- and hyper-energy impacting cases. For low impacting energy, dust particles stick on PFM surface without damaging it. Two typical time points exist and the temperature of PFM grows all the time but PFM structure experience a modifying process. Under high energy case, three typical points appear. The temperature curve fluctuates in the whole interaction process which indicates there are dust/PFM and kinetic/potential energy exchanges. In the hyper-energy case in present simulation, the violence dust/PFM interactions cause sputtering and crater investigating on energy evolution curves. We further propose the statistics of energy distribution. Results show that about half of impacting energy consumes on heating plasma-facing material meanwhile the other half on PFM structure deformation. Only a small proportion becomes kinetic energy of interstitial or sputtering atoms. [ABSTRACT FROM AUTHOR]

A series of benzoyl diarylamine/ether derivatives were designed, synthesized, and evaluated for their activity against human immunodeficiency virus ( HIV) in MT-4 cells. Three compounds ( 3b, 5a, and 6a1) exhibited moderate activities against wild-type (wt) HIV-1 with EC50 values ranging from 11 to 56 μ m. Among them, compound 5a was the most potent inhibitor with a novel chemical skeleton, affording a new lead compound for further molecular optimization. An enzyme assay was also implemented to confirm the binding target of the active compounds represented by 6a1. Molecular simulation studies on compound 5a, 6a1, and 7a4 were carried out to understand their binding mode with wt HIV-1 reverse transcriptase ( RT) and provided useful information for further rational design of NNRTIs. [ABSTRACT FROM AUTHOR]

In present research, the sputtering and reflection yield of self-bombardment of tungsten are investigated with the aid of molecular dynamics simulations. The source of sputtered and reflected atoms is detected by traced the original locations of sputtered and reflected atoms. Results show that for the reflected atoms no specific region exists which means cluster atoms are randomly reflected. But almost all of sputtered atoms are from a conical region under the landing point of cluster. So we can determine the sputtering yield by study the dimension of the sputtering region. Molecular dynamics shows the depth and radius of the conical are power functions of impacting energy. The effects of cluster size and temperature of target on sputtering and reflection rate are also preformed in present study. Both sputtering and reflection yield are proportion to cluster size in present cluster size, i.e. 66–2647 atoms. Higher target temperature can increase sputtering yield and deduce sputtering threshold energy, but little effect on reflection rate. [ABSTRACT FROM AUTHOR]

• Evolution of adjacent liquid bridges is conducted by molecular dynamics simulation. • Mismatch rate M ∗ and horizontal spacing D h can effectively control the coalescence and jumping of adjacent droplets. • Van der Waals parameter ε ∗ will reduce the wettability of kaolinite, while CO 2 saturation is the opposite. • The orderly arrangement of water and CO 2 molecules is related to the interface. • Coalescence/jumping coalescence contributes to the rise of capillary force, leading to the instability of system. The mechanism of mechanical and hydraulic properties of unsaturated clays at the nanoscale hasn't been fully understood, especially for three-phase systems. Through molecular dynamics (MD) and a series of microscopic test methods, the stability of kaolinite-water-CO 2 under D h , S r , M ∗ , d s ∗ and ε ∗ was evaluated. The results of density field, adsorption, contact angle and capillary force of water and CO 2 molecules indicated that D h and M ∗ controlled the coalescence and jumping of adjacent droplets, while the wettability of minerals depended on S r and ε ∗ . When the two droplets ranged from coalescence to separation, not only the contact angle enlarged, but the capillary force declined. Although the rise of ε ∗ will enhance the wettability of kaolinite, it will cause the liquid bridge to break and be adsorbed on the surface of particle in the form of a liquid film if it's too high. In this case, contact angle of liquid bridges suddenly dropped to zero. The capillary force will also present a trend of first increasing and then decreasing. In the three-phase environment, the enlargement of S r induced CO 2 molecules to be adsorbed on the surface of solid and liquid phase due to hydrogen bonds, thereby reducing the wettability of minerals. Subsequently, capillary force became smaller. In addition, CO 2 and H 2 O molecules at the interface were arranged in order, and the thickness of adsorption layer was from small to large: solid–gas, solid–liquid, gas–liquid. By fitting the critical conditions of liquid bridges in instability and fracture, it may be beneficial to explain macroscopic unsaturated theory and long-term experimental observations. [ABSTRACT FROM AUTHOR]

One way to increase the ductility of metallic glasses is to induce heterogeneous microstructures, as for example in nanoglasses and crystal-glass composites. The heterogeneities have important consequences not only on the development of shear bands, but also on the structural relaxations in the glass phase. Experiments using dynamic mechanical spectroscopy (DMS) have been conducted, but an atomic-scale picture is still lacking. Here we apply DMS within molecular dynamics simulations to a classical CuZr metallic glass to study how structural relaxations and mechanical energy dissipation are affected by different microstructures, including nanoglasses, crystal-glass nanolaminates and glasses with spherical crystalline inclusions. We find that in a fully glassy system, not only the fraction but also the spatial homogeneity of "hard" icosahedral environments matter. When hard crystalline particles are introduced, the storage modulus simply results from volumetric averages consistent with the classical Voigt and Reuss bounds. On the other hand, loss moduli are much more complex and can be smaller or larger than in a pure glass depending on the microstructure and loading condition. Atomistic processes leading to these evolutions are discussed and remaining open questions are highlighted. [Display omitted] [ABSTRACT FROM AUTHOR]

The static and dynamic mechanical behaviors of atoms/ions migrating on graphene surface are investigated via theoretical and numerical calculations, and a design idea of nano-scale device that can be used for atoms/ions screening is proposed on this basis. By using the Fourier expansion of the interaction potential between atoms, the analytical expression of the interaction force between an atom/ion and infinitely large graphene is derived. The dependence of the interaction force on the vertical distance from the atom/ion to graphene surface and the atomic/ionic types are analyzed. Based on the interaction force, a dynamics governing equation for the migration of atoms/ions on graphene surface is established, and the dynamics behaviors of atoms/ions when they migrate on the graphene surface at different initial velocities are studied. Taking lithium-ion as an example, it is found that there are three migration states along the armchair direction of graphene. No matter which migration state, the lithium-ion will eventually be stably adsorbed above the center of a hexagonal carbon ring (the hollow site). By adjusting the initial velocity, the lithium-ion can be steadily adsorbed at the specified sites, so as to control the migration distance of lithium-ion. What's more, the functional relationship between the critical initial velocity of the lithium-ion and the stable adsorption sites on graphene surface is given, and the influence of the vertical distance from the lithium-ion to graphene surface on the migration process is analyzed. In addition, the dynamics behaviors of the migration of different atoms/ions on graphene surface are studied, and it is found that the migration of alkali metal particles is more free with the increase of atomic number, and the stable site is further away from the initial position, which is in good agreement with the results of molecular dynamics simulation in the literature. Besides, the effects of initial position, damping and migration path on the dynamics behaviors of atoms/ions migrating on graphene surface are also studied. Finally, on the basis of theoretical results, a design idea of graphene-based nano-scale device is proposed, which can be used to screen specified atoms/ions and control their in and out positions. Image 1 • The mechanical behaviors of atoms/ions migrating on graphene are investigated. • The dependence of dynamics behavior of atoms/ions on initial velocity is studied. • The influence of atomic/ionic types on the dynamics behavior is described. • The effects of initial position, damping and migration path are considered. • A design idea of graphene-based nanodevice for atoms/ions screening is proposed. [ABSTRACT FROM AUTHOR]

• Texturing effects on nanotribological properties and subsurface damage are studied. • Nanoscale friction and wear behaviour of GaN can be regulated by texture parameter. • Nano-texture can alleviate dislocation development and reduce subsurface damage. • The m -GaN exhibits lower wear and thicker damage layer compared with the c -GaN. Surface nanotribological properties and subsurface damage of flat and textured gallium nitride (GaN) substrates during both linear and circular nanoscratching processes are investigated using molecular dynamics simulation. Results show that the surface texture can remarkably reduce not only the surface friction and wear but also the scratching-induced subsurface damage regardless of the tip radius and penetration depth. Tangential force and friction coefficient decreased with an increase in groove width or depth primarily due to the reduced contact area. The effect of texturing on stress distribution can affect the development of dislocation to alleviate the nanoscale material deformation and removal and thereby reduce surface wear and subsurface damage. Increasing tip radius can reduce the friction coefficient and surface wear, but it promotes subsurface damage. By contrast, increasing tip penetration depth can increase the friction, wear, and subsurface damage for flat and textured GaN substrates. Compared with the c -plane, the m -plane GaN substrate exhibits higher friction but lower material wear, and it has a considerably thicker subsurface damage layer due to the difference in their dislocation networks. This work can provide useful insights into the design of GaN-based material with antifriction and wear properties through the surface texturing treatments. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations were used to explore the effect of abrasive size on the nano abrasive machining for wurtzite gallium nitride (GaN) single crystal. The deformation behaviours, varied with the abrasive size, were systematically analysed. The simulation results show that increasing the abrasive size results in more severe plastic deformation and machining-induced hardening, which consequently cause an increase in atomic temperature, strain, stress, and cutting forces. The use of larger abrasive produces greater compression, thus boosts the elastic recovery and damages the subsurface of GaN single crystal much heavily, with the enhancement of the nucleation and emission of dislocation, and the local phase transition from B4 to B3 structure or even to fivefold hexagonal structure. The development of pile-up and amorphization is impressively inhibited by increasing abrasive size, suggesting that the cutting effect could be impaired using a larger abrasive under a given depth of cut. • The effect of abrasive size on the nano abrasive machining for GaN single crystal is investigated via MD simulation. • Both plastic deformation and machining-induced hardening become severe as the abrasive size increases. • The development of pile-up and amorphization is impressively inhibited by increasing abrasive size. • The cutting effect can be impaired using a greater abrasive under a given depth of cut. [ABSTRACT FROM AUTHOR]

The negative Poisson's ratio (NPR) of graphene is studied via molecular dynamics (MD) simulations when epoxy groups are orderly arranged on its surface. When two epoxy groups are located on the same side of the zigzag bridge in a representative cell of graphene, a ripple area appears on the graphene surface. A truss structure model of the ripple is presented to reveal the nature of the NPR phenomenon due to the de-wrinkling effect during stretching. Based on this, the wrinkle region is defined as a periodic distribution unit, and it is evenly distributed along the X- and Y-direction in the 5 nm × 5 nm graphene, then it is found that graphene exhibits a remarkable negative Poisson's ratio phenomenon. In addition, the results show that the oxygen atoms proportion of graphene significantly influence its NPR, and the NPR is the most remarkable when the proportion of oxygen atoms is 4.2 %. [Display omitted] • NPR of graphene caused by epoxy group was studied by theoretical and MD method. • A truss structure model was presented to reveal the nature of NPR phenomenon. • The designed graphene containing epoxy groups exhibits remarkable NPR phenomenon. • NPR of graphene containing epoxy groups depends on the proportion of oxygen atoms. • GO with 4.2 % oxygen atoms has the most remarkable NPR. [ABSTRACT FROM AUTHOR]

Microscale experimental techniques are challenging in terms of test time, sample preparation, and resolution. It is also difficult for molecular dynamics (MD) to overcome spatial and temporal limitations. Wyoming sodium montmorillonite was used in this study. Based on the Gay-Berne potential (GB), the unloading properties of clay aggregates under different environmental conditions were simulated using coarse-grained molecular dynamics (CGMD) method. The results showed that for each case, the deformation was closely related to the distribution of the stacks. In particular, the relationship between the total number of stacks and void ratio followed the Boltzmann distribution. At the same time, it was found that the stress states in different cases during unloading depend on the particle orientation. For one-dimensional unloading, the particle arrangements exhibited significant anisotropy, leading to a smaller vertical rebound. Owing to the isotropic compression at 1 atm and lateral confinement, the lateral pressure coefficient (k) is >1 in the atmospheric environment. In contrast, limited lateral expansion caused k to be smaller than 1 in a vacuum. With decreasing confining pressure, a linear increase in the void ratio was observed. During this process, the number of small-sized stacks gradually decreased, accompanied by an increase in the number of large-sized stacks. From 100 MPa to 1 MPa, the longer the unloading path, the smaller the rebound. In the range of 0.1–0.7 MPa, the clay configurations reached equilibrium and the unloading paths had no obvious effects on the distribution of stacks. This work demonstrates the validity of the GB potential model, which provides a basis for bottom-up mechanical prediction of the hierarchical structure of Na-montmorillonite particles. [Display omitted] • The effects of environments and loading conditions on the rebound were obvious. • The relationship between N t and void ratio followed the Boltzmann distribution. • Changes in lateral stresses were mainly determined by particle orientation. • Gay-Berne potential reliably reproduce the unloading process of clay aggregates. [ABSTRACT FROM AUTHOR]

The Poisson's ratio of the in-plane pristine armchair and zigzag graphene under uniaxial tensile loading is studied by molecular dynamics simulations, which indicates that Poisson's ratio strongly depends on the tensile strain. At the critical strain, the Poisson's ratio will transform from positive to negative, and the critical strain of the zigzag is far less than that of armchair. The study on the representative cell of graphene shows that the intrinsic nature of strain-induced negative Poisson's ratio (NPR) is the competition between the variation rates of bond length and bond angle. Meanwhile, the critical strain that induces NPR has significant size effects, which depends on the proportion of representative cells at the width boundary in the whole graphene. What's more, 5-8-5 defect has a significant effect on the NPR phenomenon of graphene. By introducing 5-8-5 defects into in-plane graphene, the critical strain value that induces NPR can be effectively regulated by adjusting the distribution modes and percentage of defects. The distributions of 5-8-5 defects adjacent to each other in the X-direction and Y-direction can significantly reduce the critical strain value. Furthermore, by increasing the percentage of 5-8-5 defects in graphene, the critical strain value can be reduced to about 50%, and the 5-ring defect plays a vital role in reducing the critical strain value. Based on this, a penta-graphene consisting entirely of 5-rings is constructed, and its Poisson's ratio is studied. The results confirm that the critical strain that induces NPR is 0. In a word, the NPR of in-plane pristine graphene can be induced by tensile strain, 5-8-5 defects can regulate the critical strain value of NPR, and penta-graphene is a perfect NPR material. [Display omitted] • Poisson's ratio will transform positive to negative at critical strain. • NPR originates from competition between the variation rates of bond length and bond angle. • The critical strain that induces NPR of graphene has significant size effects. • The distributions and percentage of 5-8-5 defects significantly reduce the critical strain. • The critical strain that induces NPR for a penta-graphene consisting entirely of 5-rings is 0. [ABSTRACT FROM AUTHOR]

Tungsten (W) and W alloys are regarded as the most promising candidates for plasma facing materials (PFMs), which will be widely used in the next generation of fusion reactors. However, blistering in W-PFM induced by extremely high fluxes of low-energy hydrogen (H) and helium (He) ions irradiation will seriously influence the plasma stability and limits the lifetime of PFM. We systematically investigate the interaction between H and He interaction in W using molecular dynamics (MD) calculations. The vacancy clusters can capture a large amount of H/He, and the H-He-vacancy clusters have much higher binding energy to He than to H. The binding energy of H-He-vacancy clusters to vacancy/W is positive, and H-He-vacancy clusters have strong trapping of W atoms and vacancies. He will strongly affect the H behavior in W, He atoms and He cluster will trap H atoms, thereby preventing the diffusion of H in W. [ABSTRACT FROM AUTHOR]

• Nano abrasive machining of monocrystalline GaN is studied by molecular dynamics simulations. • Deformation of monocrystalline GaN is associated with both the propagation of dislocation and the contact of workpiece/tool. • Dislocation and phase transition are identified in the deformation layer after nano abrasive machining. • Pile-up and elastic recovery of monocrystalline GaN are affected by the stagnation region and slip system. • Effects of cutting velocity, depth of cut and abrasive shape on deformation are systematically investigated. Molecular dynamics simulations are carried out to investigate the nano abrasive machining of monocrystalline gallium nitride (GaN). Effects of the cutting velocity, depth of cut (DOC) and abrasive shape on the atomic strain, stress, temperature, cutting forces, and deformation layer are systematically investigated, aiming at understanding the deformation behaviour of monocrystalline GaN during nano abrasive machining. The results show that the strain, stress and temperature were increased by using the higher cutting velocity, the larger DOC or cub-octahedral abrasive. Being affected by both the average stress and the elasto-plastic deformation zone right ahead the diamond particle, the cutting forces increase with the increase in DOC but decrease under a larger cutting velocity, or when using a cub-octahedral abrasive. The deformation layer in the subsurface is insensitive to the cutting velocity, while impressively shrinks under a larger DOC or cub-octahedral abrasive used. As the stress and temperature rise, the use of higher cutting velocity, larger DOC or cub-octahedral abrasive would facilitate the nucleation of dislocation, phase transition and the development of pile-up. This work can enrich the understanding on the nanoscale deformation mechanism of monocrystalline GaN material during the ultra-precision machining process. [ABSTRACT FROM AUTHOR]

Abstract Atomic-level studies have been performed to investigate the hydrogen behavior near a 1/2<111>{110} edge dislocation and a 1/2<111> screw dislocation in α iron. Molecular statics analysis has been carried out to determine the stress distributions and hydrogen binding energy around the dislocation cores. The results reveal that the hydrogen binding is more sensitive to the hydrostatics stress than the shear stress around the edge dislocation, while the shear stress plays a leading role on the hydrogen binding around the screw dislocation. In addition, nudged elastic band (NEB) calculations have been applied to explore different migration paths and the corresponding migration energy barriers of a single hydrogen atom at the dislocation cores. It is of interest to note that both edge and screw dislocations are not able to offer fast pipe diffusion of hydrogen atoms along the dislocation line, as normally considered. Instead, hydrogen atoms prefer to diffuse slowly along oblique paths crossing the edge dislocation line on the slip plane and spiral paths surrounding the screw dislocation line. Furthermore, molecular dynamics simulations have been performed to study the diffusion behavior of hydrogen at the dislocation cores, which verifies the results of NEB calculations. Highlights • The distribution of the stress and hydrogen binding energies around the dislocations together with their correlations. • Neither the edge nor screw dislocations can provide fast diffusion pipes for hydrogen in α iron. • The hydrogen diffusion mechanism near the dislocation cores at different temperatures. [ABSTRACT FROM AUTHOR]

In recent years, a delivery system based on atomic force microscopy (AFM) has been developed to transport nucleic acids, proteins and drugs to single adherent cell by controlling the indentation process. However, the transportation efficiency is limited by the low penetration rate of the common commercial AFM probe. The tip of commercial AFM probe is blunt and it is hard for blunt tip to insert into the soft cell membrane. In this study, dissipative particle dynamics (DPD) simulations were applied to investigate the penetration process of the AFM probe into the cell membrane subjected to different strain states. It was observed that the AFM tip moved down a shorter distance to penetrate the stretched lipid membrane compared with unstretched membrane. Moreover, the threshold value of penetrating force decreased as cell membrane extended. The short indentation time and small force can reduce the probability of cell membrane collapse, therefore it is easier for the AFM tip to penetrate the cell. We also performed the AFM indentation experiments via AFM to investigate the relationship between penetrating force and indentation speed. This work provides a potential way to improve the efficiency of cell transfection by using the AFM delivery system. [ABSTRACT FROM AUTHOR]

Soil and ground water pollution by heavy metal is an identified global environment concern. Montmorillonite is widely adopted as an adsorbent used in retardation of heavy metals due to its excellent adsorption capacity, conveniency, and stability. However, the adsorption mechanism of heavy metal ions in the interlayer and nanopore of montmorillonite needs to be further studied. The classical grand canonical monte carlo (GCMC) and molecular dynamics (MD) simulations were performed to quantify the structural and dynamic properties of heavy metal ions in the interlayer and nanopore of montmorillonite (MMT). Two layer charge densities of MMT, two cation concentrations, and three typical heavy metal ions (Pb2+, Ba2+, and Cs+) were considered. With the increase of layer charge density, outer-sphere adsorption (OSA) was transformed into inner-sphere adsorption (ISA) for three heavy metal ions. The adsorption quantity increased with the increase of layer charge density and cation concentration. The calculated diffusion coefficients of three heavy metal caions in montmorillonite was bulk solution > nanopore > interlayer. The results and adsorption mechanism are helpful for understanding the natural processes of heavy metal ions in environment and developing more efficient remediation materials. [Display omitted] • Outer-sphere adsorption occurred for Pb2 + and Ba2 + on low-charge montmorillonite surface. • The adsorption capacity of high-charge montmorillonite was stronger than low-charge montmorillonite. • Higher cation concentration increases adsorption quantity but doesn't change adsorption pattern. • The mobility of cations in montmorillonite follow the order of interlayer < nanopore < solution. [ABSTRACT FROM AUTHOR]

• A possible mechanism for the formation of vacancy dislocation loops in α-Fe is proposed. • Vacancy-NH clusters prefer to shape into 2D clusters, especially on (211) planes. • The presence of H can greatly promote the growth of vacancy dislocation loops. Genetic algorithm was applied to search the energy minimization configuration of vacancy clusters in α-Fe. Molecular statics calculations and dynamics annealing relaxation were employed to calculate the formation and binding energies of vacancies and 3D vacancy or vacancy-hydrogen (H) clusters, as well as 2D vacancy or vacancy-H clusters on (111), (011) and (211) planes. Our calculations show that vacancies prefer to form 3D clusters and vacancy dislocation loops are difficult to form, while vacancy-H clusters prefer to shape into 2D clusters, especially on (211) planes. Since H prefers the directional bonding, a vacancy cluster with H atoms tend to form a vacancy dislocation loop with its slip direction along the 〈100〉 direction and on the (211) habit plane. Our results are consistent with the experimental observations, and provide a possible mechanism for the formation of vacancy dislocation loops in α-Fe. Furthermore, we have also explored how dislocation loops trap self-interstitial atoms, vacancies and H atoms. It is of interest to note that H atoms strongly bound to a 〈100〉 vacancy dislocation loop, and are able to enhance the ability for the dislocation loop to further trap vacancies and reduce its ability to absorb self-interstitial atoms, thus promoting the growth of the 〈100〉 vacancy dislocation loops. [ABSTRACT FROM AUTHOR]

Tiansi Liquid is a traditional Chinese herbal medicine used to treat depression; however, the underlying mechanisms remain unclear. Here, we examined the effect of Tiansi Liquid in a rat model of hydrocortisone-induced depression using behavioral testing, 16S rRNA high-throughput pyrosequencing and high-performance liquid chromatography-mass spectrometry-based metabolomics of the tryptophan (TRP)–kynurenine (KYN) pathway. Tiansi Liquid significantly improved the sucrose preference and exploratory behavior of the depressive rats. The richness of intestinal mucosa samples from the model (depressive) group tended to be higher than that from the control group, while the richness was higher in the Tiansi Liquid-treated group than in the model group. Tiansi Liquid increased the relative abundance of some microbiota (Ruminococcaceae, Lactococcus, Lactobacillus, Lachnospiraceae_NK4A136_group). Metabolomics showed that Tiansi Liquid reduced the levels of tryptophan 2,3 dioxygenase, indoleamine 2,3-dioxygenase, quinoline and the KYN/TRP ratio, while increasing kynurenic acid and 5-HT levels. Correlation analysis revealed a negative relationship between the relative abundance of the Lachnospiraceae_NK4A136_group and quinoline content. Collectively, these findings suggest that Tiansi Liquid ameliorates depressive symptoms in rats by modulating the gut microbiota composition and metabolites in the TRP–KYN pathway. [ABSTRACT FROM AUTHOR]