Search

The information engine is a feedback mechanism that extorts work from a single heat bath using the mutual information earned during the measurement. We consider an overdamped active Ornstein–Uhlenbeck particle trapped in a 1D harmonic oscillator. The particle experiences fluctuations from an inherent thermal bath with a diffusion coefficient (D) and an active reservoir, with characteristic correlation time (τa) and strength (Da). We design a feedback-driven active Brownian information engine (ABIE) and analyze its best performance criteria. The optimal functioning criteria, the information gained during measurement, and the excess output work are reliant on the dispersion of the steady-state distribution of the particle's position. The extent of enhanced performance of such ABIE depends on the relative values of two underlying time scales of the process, namely, thermal relaxation time (τr) and the characteristic correlation time (τa). In the limit of τa/τr → 0, one can achieve the upper bound on colossal work extraction as ∼ 0.202 γ (D + D a ) (γ is the friction coefficient). The excess amount of extracted work reduces and converges to its passive counterpart (∼ 0.202 γ D) in the limit of τa/τr → high. Interestingly, when τa/τr = 1, half the upper bound of excess work is achieved irrespective of the strength of either reservoirs, thermal or active. Finally, we look into the average displacement of active Brownian particles in each feedback cycle, which surpasses its thermal analog due to the broader marginal probability distribution. [ABSTRACT FROM AUTHOR]

By simulation and asymptotic theory, we investigate the transition-path time of a one-dimensional finite-mass reaction coordinate crossing a double-well potential in the presence of non-Markovian friction. First, we consider single-exponential memory kernels and demonstrate that memory accelerates transition paths compared to the Markovian case, especially in the low-mass/high-friction limit. Then, we generalize to multi-exponential kernels and construct an asymptotic formula for the transition-path time that compares well with simulation data. [ABSTRACT FROM AUTHOR]

Cold spray is an effective method for surface coating, which has been applied in various engineering areas. However, it is difficult to directly observe the dynamic deformation process in experiments. This paper applies the molecular dynamics simulation to model the deposition of a monocrystalline Cu particle onto a Cu substrate and, subsequently, carries out a systematic study on the deposition mechanism and microstructure evolution. The results indicate that the deposition process consists of an impact stage and a relaxation stage. It is mainly the high speed collision and the friction following the collision that lead to particle deposition, which, under different circumstances, can be defined as surface deposition or penetration deposition. Two methods, namely, drastic shear deformation and cooling in the relaxation stage, can help form nanocrystallines. Jetting and melting are not the necessary factors for the deposition of nano-sized particles. The formation of dislocation lines is influenced by impact velocities. At lower impact velocities, the dislocation lines are mainly distributed near the contact surface. However, when the impact velocity is higher, dislocation lines are almost uniformly distributed in the particle. [ABSTRACT FROM AUTHOR]

Electronic friction and Langevin dynamics is a popular mixed quantum–classical method for simulating the nonadiabatic dynamics of molecules interacting with metal surfaces, as it can be computationally more efficient than fully quantum approaches. In this work, we extend the theory of electronic friction within the hierarchical equations of motion formalism to models with a position-dependent metal–molecule coupling. We show that the addition of a position-dependent metal–molecule coupling adds new contributions to the electronic friction and other forces, which are highly relevant for many physical processes. Our expressions for the electronic forces within the Langevin equation are valid both in and out of equilibrium and for molecular models containing strong interactions. We demonstrate the approach by applying it to different models of interest. [ABSTRACT FROM AUTHOR]

We investigate whether making the friction spatially dependent on the reaction coordinate introduces quantum effects into the thermal reaction rates for dissipative reactions. Quantum rates are calculated using the numerically exact multi-configuration time-dependent Hartree method, as well as the approximate ring-polymer molecular dynamics (RPMD), ring-polymer instanton methods, and classical molecular dynamics. By conducting simulations across a wide range of temperatures and friction strengths, we can identify the various regimes that govern the reactive dynamics. At high temperatures, in addition to the spatial-diffusion and energy-diffusion regimes predicted by Kramer's rate theory, a (coherent) tunneling-dominated regime is identified at low friction. At low temperatures, incoherent tunneling dominates most of Kramer's curve, except at very low friction, when coherent tunneling becomes dominant. Unlike in classical mechanics, the bath's influence changes the equilibrium time-independent properties of the system, leading to a complex interplay between spatially dependent friction and nuclear quantum effects even at high temperatures. More specifically, a realistic friction profile can lead to an increase (or decrease) of the quantum (classical) rates with friction within the spatial-diffusion regime, showing that classical and quantum rates display qualitatively different behaviors. Except at very low frictions, we find that RPMD captures most of the quantum effects in the thermal reaction rates. [ABSTRACT FROM AUTHOR]

Exposure to ambient air contaminates the surface of graphene sheets. Contamination may arise from different sources, and its nature alters the frictional behavior of the material. These changes in friction enable the observation of the early stages of contaminants' adsorption in graphene. Using a friction force microscope, we show that molecular adsorption initiates at the edges and mechanical defects in the monolayer. Once the monolayer is covered, the contaminants spread over the additional graphene layers. With this method, we estimate the contamination kinetics. In monolayer graphene, the surface area covered with adsorbed molecules increases with time of air exposure at a rate of 10−14 m2/s, while in bilayer graphene, it is one order of magnitude smaller. Finally, as the contaminants cover the additional graphene layers, friction no longer has a difference concerning the number of graphene layers. [ABSTRACT FROM AUTHOR]

This paper reports on the effects of shear rate and interface modeling parameters on the hydrodynamic slip length (LS) for water–graphite interfaces calculated using non-equilibrium molecular dynamics. Five distinct non-bonded solid–liquid interaction parameters were considered to assess their impact on LS. The interfacial force field derivations included sophisticated electronic structure calculation-informed and empirically determined parameters. All interface models exhibited a similar and bimodal LS response when varying the applied shear rate. LS in the low shear rate regime (LSR) is in good agreement with previous calculations obtained through equilibrium molecular dynamics. As the shear rate increases, LS sharply increases and asymptotes to a constant value in the high shear regime (HSR). It is noteworthy that LS in both the LSR and HSR can be characterized by the density depletion length, whereas solid–liquid adhesion metrics failed to do so. For all interface models, LHSR calculations were, on average, ∼28% greater than LLSR, and this slip jump was confirmed using the SPC/E and TIP4P/2005 water models. To address the LS transition from the LSR to the HSR, the viscosity of water and the interfacial friction coefficient were investigated. It was observed that in the LSR, the viscosity and friction coefficient decreased at a similar rate, while in the LSR-to-HSR transition, the friction coefficient decreased at a faster rate than the shear viscosity until they reached a new equilibrium, hence explaining the LS-bimodal behavior. This study provides valuable insights into the interplay between interface modeling parameters, shear rate, and rheological properties in understanding hydrodynamic slip behavior. [ABSTRACT FROM AUTHOR]

Coarse-grained (CG) models informed from molecular dynamics simulations provide a way to represent the structure of an underlying all-atom (AA) model by deriving an effective interaction potential. However, this leads to a speed-up in dynamics due to the lost friction, which is especially pronounced in CG implicit solvent models. Applying a thermostat based on the Langevin equation (LE) provides a way to represent the long-time dynamics of CG particles by reintroducing friction to the system. To improve the representability of CG models of heterogeneous molecular mixtures and their transferability over the mixture compositions, we parameterize an LE thermostat in which the friction coefficient depends on the local particle density (LD). The thermostat friction was iteratively optimized with a Markovian variant of the recently introduced Iterative Optimization of Memory Kernels (IOMK) method. We simulated tert-butanol/water mixtures over a range of compositions, which show a distinct clustering behavior. Our model with LD-dependent friction reproduces the AA diffusion coefficients well over the full range of mixtures and is, therefore, transferable with respect to dynamics. [ABSTRACT FROM AUTHOR]

The celebrated generalized Stokes law predicts that the velocity of a particle pulled through a liquid by an external force, Fex, is directly proportional to the force and inversely proportional to the friction ζ acted by the medium on the particle. We investigate the range of validity of the generalized Stokes law at molecular length scales by employing computer simulations to calculate friction by pulling a tagged particle with a constant force. We thus calculate friction for two model interaction potentials, Lennard-Jones and soft sphere, for several particle sizes, ranging from radius (a) smaller than the solvent particles to three times larger. We next obtain friction from diffusion (D) by using Einstein's relation between diffusion and friction ζ in an unperturbed liquid. We find a quantitative agreement between the two at a small-to-intermediate pulling force regime for all the sizes studied. The law does break down at a large pulling force beyond a threshold value. Importantly, the range of validity of Stokes' scheme to obtain friction increases substantially if we turn off the attractive part of the interaction potential. Additionally, we calculate the viscosity (η) of the unperturbed liquid and find a good agreement with the Stokes–Einstein relation ζ = Cηa for the viscosity dependence with a value of C close to 5 π, which is intermediate between the slip and stick boundary condition. [ABSTRACT FROM AUTHOR]

The rates and pathways of chemical reactions at metal surfaces can be strongly influenced by energy dissipation due to the nonadiabatic excitation of metallic conduction electrons. The introduction of frictional forces to account for this dissipation has been quite successful in situations for which the nonadiabatic coupling is weak. However, in cases where nonadiabatic coupling is strong, such as when electron transfer occurs, the friction model is likely to break down. Ryabinkin and Izmaylov have proposed 2-state and 3-state alternatives to the friction model for introducing electronic dissipation in molecular dynamics simulations. Here, we examine their 2-state model using some simple examples of atom–surface scattering. We find that, with the addition of decoherence, the 2-state model can produce quite promising results. [ABSTRACT FROM AUTHOR]

OBJECTIVE: Fibrin sealants are routinely used for intra-articular surgical fixation of cartilage fragments and implants. However, the mechanical properties of fibrin sealants in the context of cartilage repair are unknown. The purpose of this study was to characterize the adhesive and frictional properties of fibrin sealants using an ex vivo model. DESIGN: Native bovine cartilage-bone composites were assembled with a single application of Tisseel or Vistaseal. Composites were tested in tension and lap shear. In addition, the coefficient of friction (COF) was measured in a native cartilage annulus model alone and with minced cartilage. Finally, the effect of a double application of fibrin sealant was evaluated. RESULTS: There were no significant differences in tensile modulus, ultimate tensile strength (UTS), shear modulus, or ultimate shear strength (USS) between the 2 fibrin sealants. Both fibrin sealants demonstrated a UTS and USS of

The molecular dynamics with electronic friction (MDEF) approach can accurately describe nonadiabatic effects at metal surfaces in the weakly nonadiabatic limit. That being said, the MDEF approach treats nuclear motion classically such that the nuclear quantum effects are completely missing in the approach. To address this limitation, we combine Electronic Friction with Ring Polymer Molecular Dynamics (EF-RPMD). In particular, we apply the averaged electronic friction from the metal surface to the centroid mode of the ring polymer. We benchmark our approach against quantum dynamics to show that EF-RPMD can accurately capture zero-point energy as well as transition dynamics. In addition, we show that EF-RPMD can correctly predict the electronic transfer rate near metal surfaces in the tunneling limit as well as the barrier crossing limit. We expect that our approach will be very useful to study nonadiabatic dynamics near metal surfaces when nuclear quantum effects become essential. [ABSTRACT FROM AUTHOR]

An analysis of plasma density distributions at arbitrary ion–atom collisionality for one-dimensional axially symmetrical cylindrical and annular plasmas is presented. Perturbations of plasma densities caused by a cylindrical probe are studied for arbitrary ion–atom collisionality. Analytical expressions for the plasma characteristics near the probe for low collisionality have been obtained. The plasma was modeled by the hydrodynamic neutral plasma equations, taking into account ionization, ion inertia, and a non-linear ion frictional force, which dominates the plasma transport at low gas pressures. Significant plasma density depletion around the probe has been observed for a wide range of ion–atom collisionality. The presented results predict underestimation of plasma density obtained from the classical Langmuir probe procedure and should provide a better understanding of electrostatic, magnetic, and microwave probes inserted into plasmas at low gas pressure. [ABSTRACT FROM AUTHOR]

The magnitude of the dipole effect detected by the cutoff energy measurement was modulated for SrTiO3 (STO)/LaAlO3 (LAO)/SrRuO3 (SRO)/STO (001) subs. epitaxial stacks by ultrathin SrAlOx (SAO) insertion prior to LAO deposition. The difference in frictional forces on the LAO surfaces between the stacks with and without SAO insertion was clearly detected by lateral force microscopy (LFM), which indicated the change in dominating surface atomic layers. From the statistical analysis of LFM images, the SAO insertion was found to improve the lateral uniformity of the stacking sequence of charged monatomic layers in epitaxial LAO along the c-axis [(LaO)+ and (AlO2)−], taking account of the inevitable correlation between the surface-terminating atoms with the stacking sequence of the charged monatomic layers in epitaxial LAO. These results are consistently explainable with the proposed model that the interface dipole effect along the c-axis of the perovskite epitaxial stack is determined by the stacking sequence of charged monatomic layers of LAO. [ABSTRACT FROM AUTHOR]

The complex dynamics of tribofilm formation on boundary-lubricated steel surfaces were investigated in real time by combining in situ measurements of the temporal variation of the coefficient of friction and contact voltage. Sliding experiments were performed with various blends consisting of base oil, zinc dialkyl dithiophosphate (ZDDP) additive, and two different dispersants at an elevated oil temperature for a wide range of normal load and fixed sliding speed. The evolution of the transient and steady-state coefficient of friction, contact voltage, and critical sliding distance (time) for stable tribofilm formation were used to evaluate the tribological performance of the tribofilms. The blend composition affected the load dependence of the critical sliding distance for stable tribofilm formation. Tribofilm friction was influenced by competing effects between the additive and the dispersants. Among various formulations examined, the tribofilm with the best friction characteristics was found to be the blend consisting of base oil, a small amount of ZDDP, and a bis-succinimide dispersant treated with ethylene carbonate. The results of this study demonstrate the effectiveness of the present experimental approach to track the formation and removal of protective tribofilms under boundary lubrication conditions in real time.

Using particle-resolved computer simulations, we investigate the effect of friction on the packing structure of hard-sphere mixtures with two kinds of particles under external compression. We first show that increasing friction between the particles results in a more disordered and less efficient packing of the local structure on the nearest neighbor scale. It is also found that standard two-point correlation functions, i.e., radial distribution function and static structure factor, show basically no detectable changes beyond short-range distances upon varying inter-particle friction. Further analysis of the structure using a four-point correlation method reveals that these systems have on the intermediate-range scale a three-dimensional structure with an icosahedral/dodecahedral symmetry that exhibits a pronounced dependence on friction: small friction gives rise to an orientational order that extends to larger distances. Our results also demonstrate that composition plays a role in that the degree of structural order and the structural correlation length are mainly affected by the friction coefficients associated with the more abundant species. [ABSTRACT FROM AUTHOR]

Rare events include many of the most interesting transformation processes in condensed matter, from phase transitions to biomolecular conformational changes to chemical reactions. Access to the corresponding mechanisms, free-energy landscapes and kinetic rates can in principle be obtained by different techniques after projecting the high-dimensional atomic dynamics on one (or a few) collective variable. Even though it is well-known that the projected dynamics approximately follows – in a statistical sense – the generalized, underdamped or overdamped Langevin equations (depending on the time resolution), to date it is nontrivial to parameterize such equations starting from a limited, practically accessible amount of non-ergodic trajectories. In this work we focus on Markovian, underdamped Langevin equations, that arise naturally when considering, e.g., numerous water-solution processes at sub-picosecond resolution. After contrasting the advantages and pitfalls of different numerical approaches, we present an efficient parametrization strategy based on a limited set of molecular dynamics data, including equilibrium trajectories confined to minima and few hundreds transition path sampling-like trajectories. Employing velocity autocorrelation or memory kernel information for learning the friction and likelihood maximization for learning the free-energy landscape, we demonstrate the possibility to reconstruct accurate barriers and rates both for a benchmark system and for the interaction of carbon nanoparticles in water. [ABSTRACT FROM AUTHOR]

Nanoparticles (NPs) can be highly beneficial as additives to lubricating fluids, and the tribotronic response of charged NPs tuned by external fields represents an area of great technological potential. Tribotronic response, however, is expected to be highly size dependent, which represents a significant design challenge. To explore this issue, quartz crystal microbalance and cyclic voltammetry were employed to characterize nanotribological and electrochemical behavior of platinum–nanofluid interfaces formed by aqueous suspensions of different-sized negatively charged titanium dioxide (TiO2) NPs. Suspensions of 5, 40, and 100 nm NPs were all observed to reduced interfacial frictional drag forces upon introduction into pure water in zero field conditions, with reductions for the 40 nm NPs about twice those of 5 nm particles at comparable concentrations. Suspensions of 100 nm NPs produced even greater reductions, but rapidly precipitated from the suspension when left unstirred. NPs were also driven to and from Pt electrode surfaces by applying external electric fields with varying amplitudes and modulation frequencies. For electric fields of sufficient amplitude and duration, the 40 nm TiO2 nanosuspension exhibited tribological properties consistent with a reversible electrophoretic deposition of the NPs, accompanied by changes in the electrochemical attributes and increasing interfacial drag. The 5 nm NP properties were consistent with progressive reductions in interfacial drag forces at the NP–suspension interface linked to field-induced increases in concentration. [ABSTRACT FROM AUTHOR]

The plastic flow of ultra-high molecular weight polyethylene (UHMWPE) at a frictional interface, which is critical to the wear behavior, was investigated by reactive molecular dynamics simulations. The UHMWPE substrate was found to experience various deformations during the friction process. First, some polyethylene (PE) chains could detach from the substrate because of their rapid movement. Second, the frequent motion of PE chains also resulted in the intermittent formation and breaking of cavities between intermolecular PE chains. These deformations were more obvious on a surface with a convex protrusion, where the plowing effect exacerbated the cavitation and elastic deformation of PE chains. Correspondingly, the plastic flow in turn reconstructed the convex protrusion by displacing the surface atoms on the Fe slab. The plastic flow of PE chains broke the C–C bonds, and the carbon moieties were then chemically bonded onto the metal surface. A rapid change of atomic charge, hence, happened when the bonds broke. Meanwhile, PE chains release short alkyl radicals gradually after bond breakage, indicating gradual wear of the substrate during friction. This work provides molecular insight into the evolution of interfacial microstructure under plastic flow on a UHMWPE substrate. [ABSTRACT FROM AUTHOR]

In braking materials field, MAX phase has been introduced into Cu-based composite materials to address issues such as inadequate wetting between ceramic particles and the metal matrix. This study focuses on preparing Ti 2 AlN-ZrO 2 -B 4 C reinforced Cu-based materials via the powder metallurgy method, and investigates the effects and mechanisms of different Ti 2 AlN/ZrO 2 ratios on the mechanical, thermal, and tribological properties of these materials. The addition of an appropriate amount of Ti 2 AlN (3 wt%) can enhance the densification and mechanical properties of Cu-based materials, as the diffusion of Al atoms promotes the sintering process. Similarly, the diffusion of Al also improves the thermal conductivity at grain boundaries, resulting in samples with higher Ti 2 AlN content exhibiting superior thermal diffusivity. When the Ti 2 AlN content reached 7 wt%, the material exhibited optimal hardness (43.35 ± 1.05 HBW), moderate shear strength (19.84 ± 1.86 MPa), as well as excellent high initial braking speed friction coefficient and stability. The reinforcement primarily arises from the diffusion bonding between Ti 2 AlN and Cu, leading to the formation of Cu-Ti compounds at the interface, which facilitates Ti 2 AlN in providing frictional force during the friction process and promotes the formation of a friction film due to the "pinning effect". Additionally, the layered structure of Ti 2 AlN and the subsequent formation of amorphous Al 2 O 3 after oxidation contributed to the enhancement of friction stability. [ABSTRACT FROM AUTHOR]

Marine water‐lubricated bearings have the advantages of environmental friendliness and long replacement cycle. However, when under the complex lubrication circumstance, the frictional and vibrational behaviors of water‐lubricated bearing always dissipate the mechanical energy output from the ship's diesel engine. Aiming at this problem and combining with previous research findings, in this paper, ceramic balls with similar mechanical properties to ship's main shaft were selected as the friction counterpart to simulate the operating conditions of marine water‐lubricated bearing. Meanwhile, dual nanoparticles of tungsten disulfide (WS2) and titanium dioxide (TiO2) were used to modify ultra‐high molecular weight polyethylene (UHMWPE) bearing material. The tribological and vibrational properties of the prepared composites were carefully investigated. The results showed that compared to pure UHMWPE, with the synergistic effect of 0.75 wt% WS2 and 0.9 wt% TiO2, the frictional and vibrational behaviors of the composites were reduced by 43.3% and 42.7%. Mechanical testing and microscopic characterization revealed the enhancement mechanism of these nanoparticles on UHMWPE. This study proposed a design strategy on marine water‐lubricated bearings for engineering application. [ABSTRACT FROM AUTHOR]

This study investigated the thermomechanical behavior of an alumina calciner's lining, a critical component in alumina processing, often susceptible to maintenance issues arising from refractory failure due to erosion and cracking. Based on numerical analyses via the finite element method, the design of a refractory panel was modeled. Furthermore, the influence of geometric parameters and friction level between lining layers on the thermal and mechanical behavior of the system was evaluated. Key findings highlighted how the curvature changed the stress profiles, resulting in particular cracking patterns, where curved panels showed higher stress concentrations at the center of their edges. Empirical validation through in-situ crack pattern observations further validated the model's predictive capability. Additionally, the study evaluated the influence of friction coefficients on resulting stresses, showing their small effect relative to other factors. Analyses on design parameters indicated that stress levels generally increased with the size-to-thickness ratio, highlighting the trade-off between reducing installation time and ensuring structural integrity in panel design and application. An alternative for enhancing lining performance was explored by selecting the material, where decreasing the insulating thermal conductivity reduced the likelihood of failure of the castable layer. Ultimately, the computational numerical method developed in this study offers a robust framework for exploring various geometries and materials, providing engineers with a versatile tool for optimizing lining designs in various operational scenarios. • Panel curvature influenced stress distributions and cracking patterns in calciner linings. • Friction modestly affected tensile stresses; 0.5 is reasonable for simulations. • Stress levels increased with panel size-to-thickness ratio, affecting installation efficiency. • Lower insulating thermal conductivity reduced failure risk in the castable layer. • The developed method provides a framework for exploring various geometries and scenarios. [ABSTRACT FROM AUTHOR]

Highlights The mechanical and frictional properties of pure perfluoroelastomer, graphene (GN)/perfluoroelastomer, and carbon nanotube (CNT)/perfluoroelastomer composite systems were investigated using molecular dynamics simulations. The influence of carbon nanomaterials on the glass transition temperature, mechanical properties, and frictional behavior of perfluoroelastomers at various temperatures was evaluated. The simulation results demonstrated that the addition of GN and CNTs increased the glass transition temperature of perfluoroelastomers to varying extents. CNTs enhanced the mechanical properties of perfluoroelastomers more effectively than GN, whereas GN provided superior improvement in frictional properties compared to CNTs. Analysis of stress–strain distribution, atomic motion trajectory, interaction energy, mass density, and temperature distribution, bond orientation parameters, radial distribution function (RDF), mean square displacement (MSD), and diffusion coefficients revealed the mechanisms and differences by which GN and CNTs enhance the mechanical and frictional properties of perfluoroelastomers. Carbon nanomaterials enhance perfluoroelastomer's high‐temperature performance. CNTs provide higher mechanical strength but lower wear resistance. GN nanosheets outperform CNTs in reducing friction and wear. Molecular dynamics simulations reveal distinct enhancement mechanisms. [ABSTRACT FROM AUTHOR]

There are multiple different equipment and testing methods to perform sensitivity tests and to determine probabilities and stimulus values for sensitivity of energetic materials. In this study a Bruceton and Three-Phase Optimal Design (3POD2.0), implemented in gonogo software, statistical testing methods were compared in practice by using them to determine impact and friction sensitivity of selected energetic materials. With Bruceton method 50% of the impact sensitivity and 27% of the friction sensitivity test series had to be discarded, due to too high or low s/d ratio. With 3POD2.0 0% of impact and 18% of friction test series had to be discarded, due to an error produced by the gonogo software. The number of individual tests that had to be discarded was much lower with 3POD2.0, since the gonogo software terminates the test process at early phase, while with Bruceton the test series most often must be finished before the validity of results can be assessed. Based on these results and literary reviews it can be concluded that 3POD2.0 is a suitable replacement for Bruceton to determine 50% initiation probability, while additionally gaining the entire sensitivity curve, resulting in fewer futile tests and less wasted resources. [ABSTRACT FROM AUTHOR]

To investigate the meshing characteristics of involute spur gear pairs, a time-varying mesh stiffness (TVMS) model is developed in this study, which pays special attention to the nonlinearity of lubrication and friction in the meshing process. Here, to improve the modeling quality, four typical parameters are considered in the model, including the lubrication state, the non-Newtonian shear characteristics of the lubricant, the time-varying displacement of the asperity, and contact conditions along the meshing path. The proposed model provides an interdependence between tooth surface contact characteristics and gear comprehensive meshing stiffness, which can provide a guidance for enhancing the performance of involute spur gears. Furthermore, the effects of roughness, rotation speed, and load on TVMS are investigated, exhibiting distinct regional characteristics along the meshing path. Noticeable differences are observed in the intensity of disturbance in the meshing-in, meshing-out, single-tooth pair, and double-tooth pair contact areas. [ABSTRACT FROM AUTHOR]

Physical aging refers to relaxation of the polymer glassy state toward the amorphous state and this phenomenon affects their physical‐mechanical properties. This work investigates the effect of physical aging on polymer scratch behavior and visibility. It was shown that mechanical properties were significantly modified over the aging time, especially the yield stress, in turn affecting polymer scratch behavior. As a matter of fact, the critical load for the onset of scratch visibility was shown to increase with the aging, thus improving sensitivity of polymer to scratches. Such behavior was strictly related to the yield stress increase with the aging time. The usefulness of the present work is highlighted, and some future perspectives are discussed. [ABSTRACT FROM AUTHOR]

The low friction nature of articular cartilage has been attributed to the synergistic interaction between lubricin and hyaluronic acid in the synovial fluid (SF). Lubricin is a mucinous glycoprotein that lowers the boundary mode coefficient of friction of articular cartilage in a dose‐dependent manner. While there have been multiple attempts to produce recombinant lubricin and lubricin mimetic cartilage lubricants over the last two decades, these materials have not found clinical use due to challenges associated with large scale production, manufacturing, and purification. Recently, a novel method using codon scrambling was developed to produce a stable, full‐length bioengineered equine lubricin (eLub) in large reproducible quantities. While preliminary frictional analysis of eLub and other recombinantly produced forms revealed they can lubricate cartilage, a complete tribological characterization is lacking, with previous studies evaluating the friction coefficient only at a single dose or a single speed. The objective of this study was to analyze the dose‐dependent tribological properties of eLub using the Stribeck framework of tribological analysis. Recombinantly produced eLub at doses greater than 1.5 mg/mL exhibits friction coefficients on par with healthy bovine SF, and a maximal 5 mg/mL dose exhibits a nearly 50% lower friction coefficient than healthy SF. eLub also modulates the shift in lubrication mode of the cartilage from the high friction boundary mode to the low friction minimum mode at high concentrations. [ABSTRACT FROM AUTHOR]

In this study, we constructed molecular friction models for polytetrafluoroethylene (PTFE)/graphene composites with various defect ratios to represent their different wear stages and simulated their friction processes under different load conditions. The friction and wear mechanisms were revealed by analyzing the variations in their molecular architectures and energies during friction. The results indicate that the friction coefficient decreased with increasing load. When the load was constant, the friction coefficients of the composites containing defections were resemble, indicating that they remained unchanged in the different wear stages. The composite wear continued to increase during friction. However, the wear increment decreased gradually. In addition, by analyzing the changes in MSD, wear can be divided into initial, stable, and accelerated wear stages. Highlights: Construct PTFE/Gr molecular models to represent their different wear stages.Simulate the dynamic changes of PTFE/Gr molecular structure during friction.The influence of PTFE/Gr dynamic structural changes was revealed.Reveal the normal force variation from an energy perspective. [ABSTRACT FROM AUTHOR]

Hybrid interference‐fit bolted‐bonded (HIBB) composite joint has a wide application prospect in improving bearing capacity of the hybrid structure. In order to deeply understand its load sharing mechanism, an analytical stiffness prediction model of HIBB composite joint was established, considering the influence of interference‐fit percentage, preload, friction coefficient, adhesive property, material performance, secondary bending moment and other parameters. Corresponding experiments were carried out to determine the experimental secondary bending moment coefficient, and the accuracy of the model was further verified. Research on HIBB composite joint shows that the hybrid form increases the adhesive failure displacement but has no effect on failure load. Before adhesive failure occurs, bolted joint stiffness is small and bolt load will increase suddenly to bear the load loss caused by the adhesive failure. It is further found that load‐sharing ratio of the bolt and total load of the structure increase with the increase of interference when adhesive failure occurs. Preload and friction coefficient have limited influence on total load of the structure at this moment, but have great influence on the bearing capacity of pure bolted structure after adhesive failure. The adhesive properties have great influence on the bearing capacity of bonded joint. Low modulus high strength adhesive can improve the load‐sharing ratio of bolt and enhance the bearing capacity by reducing the overall stiffness of the structure. Bearing mechanism of the two joint forms in the hybrid one was fully revealed, which provides a theoretical method for the application of HIBB composite joint. Highlights: An analytical stiffness prediction model of HIBB composite joint was established to deeply understand its load sharing mechanism.Load sharing mechanism analysis and parametric research for the two joint forms were carried out and influences on stiffness were obtained.Low modulus high strength adhesive can improve the load‐sharing ratio of bolt by reducing the overall structure stiffness.Bearing mechanism of the two joint forms in the hybrid one was revealed. [ABSTRACT FROM AUTHOR]

AbstractThis study aims to evaluate the lubrication performance of a nano-TiO2 oil-in-water (O/W) emulsion during the hot rolling process. A series of O/W emulsions with varying concentrations of TiO2 nanoparticles (0.05, 0.1, 0.3, and 0.5 wt.%) were synthesized. Tribological tests were conducted under a load of 70 N for 10 minutes to determine the optimal concentration based on anti-frictional properties. The O/W nano-emulsion optimized with a 0.1 wt.% concentration of TiO2 applied in the hot rolling process of IS 2062 E250 grade steel. This application resulted in a reduction of rolling force (RF) and surface roughness, suggesting its potential as an alternative lubricant. The results indicated superior antifriction performance at a TiO2 concentration of 0.1 wt.%, leading to a 15% reduction in RF. Additionally, the use of the nano-emulsion contributed to a significant reduction in oxide scale formation. Surface roughness measurements of the rolled samples revealed a 19% decrease, with a roughness value of 2.125 µm, compared to samples rolled with a nano-free O/W emulsion. These findings suggest that nano-TiO2 O/W emulsions could serve as an effective alternative to conventional O/W emulsions in future industrial metalworking applications. [ABSTRACT FROM AUTHOR]

Pressure injuries, also known as pressure ulcers or 'bed sores', are caused by prolonged pressure on the skin and underlying tissues and are common in healthcare settings. They result from a variety of factors including pressure, moisture and friction, with a higher risk among older adults, post‑surgical patients and those with limited mobility or long‑term conditions. These injuries can extend hospital stays and significantly impact patient recovery and mortality risk. Prevention includes regular repositioning, the use of pressure‑relieving devices, skin care and nutritional support. The National Institute for Health and Care Excellence provides guidelines to mitigate these risks through systematic risk assessments and targeted interventions. Early detection and specialist care by a multidisciplinary team are crucial to improving patient outcomes. Consistent pplication of prevention strategies are needed to reduce incidence, improve patient care and alleviate the economic burden of thesex injuries on the NHS. [ABSTRACT FROM AUTHOR]

Polyamide 6 (PA6) thermoplastic‐based composites are often used in automobile, aerospace, marine, and biomedical applications. Here, PA6 and its composites with varied chopped glass fiber (GF) concentrations of 5, 10, and 20 mass% were fabricated by injection molding. The specimens were characterized by structural, thermal kinetic, mechanical, as well as tribological analyses. Tribological performance was evaluated in dry pin‐on‐disc test apparatus with three different levels of time, speed, and load factors. The PA6/GF composites showed high decomposition activation energy compared to pure PA6. Thermal activation, Ea increased to 46.16% with increasing of GF content up to 10 mass% in the composites compared to PA6. PA6/5GF exhibited best mechanical properties (e.g., strength = 44.46 MPa and Hardness = 45.2). Addition of GF in PA6 significantly improved tribological properties, coefficient of friction (COF) and specific wear rate (WR) besides thermal stability and mechanical properties of the composites. Especially, COF and WR of PA6/5GF composite decreased by 17%–65% and 68%–92%, respectively, compared to PA6. ANOVA statistical results determined the significant contribution of the tribological factors to the performance metrics of the composites for COF and WR. Therefore, the PA6/5GF composite would highly be useful for tie‐rod gears and bearings as a crucial structural component in automotive bodywork. [ABSTRACT FROM AUTHOR]

Drag reducers are indispensable components of slickwater fracturing fluids and play a pivotal role in the reconstitution of unconventional oil and gas reservoirs. Water‐in‐water emulsion (W/W) drag reducers have garnered significant attention owing to their rapid dissolution and environmentally benign properties. The solubility and viscosity enhancing ability of W/W drag reducers were further enhanced by synthesizing a novel W/W drag reducer through dispersion polymerization, thereby meeting the requirements of real‐time mixed fracturing construction technology. The solubility, viscosity enhancement, and synthesis state of the synthetic drag reducer were employed as evaluation criteria, whereby the synthetic systems underwent screening and optimization of the synthesis conditions. The final synthetic conditions were determined as follows: the monomer (AM and DMC) had a total mass concentration of 25 wt%, with an AM to DMC molar ratio of 95:5. The dispersion medium (sodium sulfate and sodium chloride) had a total mass concentration of 12 wt%, with a sodium sulfate to sodium chloride mass ratio of 1:2. The dispersion stabilizer PVP K60 had a mass concentration of 7 wt%. The initiator had a total mass concentration of 0.05 wt%, with an ammonium persulfate to sodium bisulfite mass ratio of 1:1. The reaction was conducted at 35°C and a stirring speed of 500 r min−1 for a duration of 8 h. The successful synthesis of the polymer was demonstrated using Fourier transform infrared spectroscopy. Environmental scanning electron microscopy and atomic force microscopy have characterized that the drag reducer has good viscosity enhancement potential. The performance evaluation results show that the solid content of drag reducer was 32.68%, and the residue content was 11.70 mg L−1. The viscosity enhancement rate of 1.3 wt% drag reducer was 93.7%. The dissolution time of 0.1 wt% drag reducer was only 25 s. The drag‐reduction rate of drag reducer reached 73.52%. Experimental results have proved that the drag reducer has the advantages of instant solubility, appreciable viscosity enhancement and drag‐reduction efficiency, fully meeting the real‐time mixing fracturing construction conditions, improving construction efficiency, and reducing construction costs. We expect that this study can broaden the application of W/W drag reducers in unconventional reservoir and provide a theoretical basis for field applications. [ABSTRACT FROM AUTHOR]

Surface-projected piles, such as helical and under-reamed piles, are widely utilized in geotechnical engineering to enhance the load-carrying capacities of pile structures with surface projection part. Despite the use of a wide variety of surface-projected conditions, detailed investigations considering various dimensions and angles of surface-projected piles remain limited in the current literature. This study aims to assess the effects of surface-projected widths wp (10 mm, 20 mm, 40 mm) and angles θ (18°, 27°, 45°, 90°) on pile penetration resistance using a two-dimensional model and PIV analysis. Wider projections increased resistance, with a maximum of 1.84 kN—57% higher than conventional piles in the model ground. Penetration resistance was proportional to width at 90°; for wp = 20 mm, penetration resistance decreased with increasing θ, while for wp = 40 mm, it increased. Theoretical ultimate bearing capacity calculations emphasize differences from experimental results due to neglected shaft friction. Residual penetration resistance and particle displacement were observed for wp of 20 mm and 40 mm after failure. This study provides insights into optimizing surface-projected pile design and understanding ground failure mechanisms. [ABSTRACT FROM AUTHOR]

The endothelial cells of the blood circulation are exposed to hemodynamic forces, such as cyclic strain, hydrostatic forces, and shear stress caused by the blood fluid's frictional force. Endothelial cells perceive mechanical forces via mechanosensors and thus elicit physiological reactions such as alterations in vessel width. The mechanosensors considered comprise ion channels, structures linked to the plasma membrane, cytoskeletal spectrin scaffold, mechanoreceptors, and junctional proteins. This review focuses on endothelial mechanosensors and how they alter the vascular functions of endothelial cells. The current state of knowledge on the dysregulation of endothelial mechanosensitivity in disease is briefly presented. The interplay in mechanical perception between endothelial cells and vascular smooth muscle cells is briefly outlined. Finally, future research avenues are highlighted, which are necessary to overcome existing limitations. [ABSTRACT FROM AUTHOR]

To improve the tribological performance of SS410 steel in seawater, TiCrN and CrSiN coatings were deposited using PVD sputtering and thoroughly analyzed. The CrSiN coating, which exhibits higher hardness and better corrosion resistance, achieved a protective efficiency of 83.70%, surpassing the TiCrN coating by 14% according to anodic polarization tests. Friction and wear properties were evaluated with a ball-on-disk tribometer in artificial seawater, following ASTM G77 standards. The CrSiN coating demonstrated lower friction coefficients and wear rates—1.362 × 10⁻⁶ mm3/N-m compared to 2.632 × 10⁻⁶ mm3/N-m for TiCrN at a 4N load—highlighting the positive impact of Si addition. These coatings markedly enhance the tribocorrosion resistance of AISI 410 steel, addressing issues in marine engine components, extending their service life, and ensuring reliable performance in severe marine conditions. SEM analysis of the uncoated SS410 surface revealed pits and deep grooves. [ABSTRACT FROM AUTHOR]

As an important turbocharging equipment, hydraulic pumps are prone to internal wear and corrosion problems. In order to improve its friction and wear performance, a ceramic coating strengthening scheme based on laser cladding technology was proposed. The roughness, thickness, width, hardness, and residual stress of the coating under different laser powers and scanning rates were measured, and the effect of process parameters on the coating structure was determined to ensure the optimal basic mechanical properties of the coating. Under the experimental conditions of 10–30 N pressure and 10–20 mm/s lubricated friction velocity, high cycle tribological tests were conducted, and the changes in average friction coefficient, wear amount, and surface wear mechanism were compared and analyzed. To verify the impact of reinforced coatings on corrosive environments, friction and wear tests were conducted in hydraulic oil environment with a pH of 6.4 and particle impurity content of approximately 5 %. Through electron microscopy, the friction morphology was observed and the wear mechanism was analyzed. In order to study the effects of different overloads (including temperature and pressure loads) on friction damage, overload friction damage analysis was conducted under low cycle fatigue loading conditions. The Rtec friction machine was applied, and the test temperature and pressure were set at 400 °C, 500 °C, 750 MPa, and 1000 MPa, respectively. The coating sample speed was set to 500 r/min and the slip rate is set to 5 %. Each sample was worn for 4 cycles under different pressures, with each cycle worn for 1 hour, then the surface roughness morphology and micro wear morphology were obtained. The research results indicate that the friction stability, wear resistance, and hardness of the coating have significantly improved, and it has stronger adaptability to hard or sharp materials, making it very suitable for the working environment of hydraulic pumps. [ABSTRACT FROM AUTHOR]

Azoxy coupling of 5‐amino‐1‐methyl‐tetrazole, 5‐amino‐2‐methyl‐tetrazole, and 5‐amino‐1‐methoxy‐tetrazole was performed by reacting each with various oxidants. These reactions revealed aqueous Oxone to be the most facile system for yielding the azoxy couple for the previously mentioned tetrazoles. Chemical and structural characterization of each novel azoxy‐coupled tetrazole was conducted with 1H NMR, 13C NMR, HRMS, and single‐crystal x‐ray diffraction. Energetic characterization was evaluated by analysis of each compounds' single crystal x‐ray diffraction density, impact sensitivity, friction sensitivity, and decomposition temperature. All compounds were found to be very sensitive to impact and friction stimuli. [ABSTRACT FROM AUTHOR]

Polymer coatings have gained a lot of attention in the recent past because of their ability to be easily coated on complex shapes, their low cost, and their ability to reduce friction as compared to other materials. Polyether ether ketone (PEEK) is one such high-performance polymer that has gained significant attention in recent years due to its exceptional mechanical properties, chemical resistance, and thermal stability making it a prominent candidate for applications in industries. However, PEEK in its pristine form exhibits poor wear resistance with a moderate coefficient of friction (0.30–0.38). Many attempts have been made by several researchers to improve its wear resistance and lower the COF by developing composite coatings. Hence, in this review, we aim to summarize and present in detail the tribological evaluation of pristine PEEK and PEEK composite coatings by discussing the various methods adopted by the researchers to improve the properties of PEEK, the different types of reinforcements and various dispersion techniques used to develop PEEK composite coatings. By consolidating and analyzing the existing body of knowledge, we also aim to offer valuable insights into the development of more durable, high-performance PEEK nanocomposite coatings for a broad range of tribological applications. [ABSTRACT FROM AUTHOR]

Rock pore structure coupled with fluid pressure plays an important role in controlling fault slip behavior. Observation of fluid-induced seismicity in geoenergy extraction has raised fundamental questions about the physics of fault rock structure and fault frictional stability in the presence of fluid. Here, we change the pore structure of faults by thermal treatment and report on the frictional stability of granite faults with pore evolution and pore fluid pressure in velocity stepping experiments under the rate-and-state framework, where the variation of pore fluid is monitored. The experiments under constant fluid pressure show that pore structure propagation leads to an increase in friction coefficient from 0.71 to 0.78. As the degree of pore propagation increases, the drained fault exhibits a transition from velocity strengthening to weakening behavior. The decrease in frictional stability could be caused by the coupling between the pore fluid and the well-connected pores, namely “fluid oscillation”. Pore pressure overpressurization could develop and cause non-uniform stress distribution along the fault surface due to pore fluid oscillation at velocity steps. The time required to equilibrate fluid pressure could be prolonged by fluid oscillation, leading to intrinsic velocity strengthening behavior appearing as velocity weakening. The decrease in rate-and-state parameter with elevating pore fluid pressure on high-porosity fault corroborates the fluid-induced fault destabilization. The fluid oscillation at the greater pore pressure could be responsible for fault reactivation. Therefore, the coupling effect of rock pore structure with pore fluid could be a potential mechanism governing fault frictional stability. [ABSTRACT FROM AUTHOR]

In this paper, the structure of the incremental quasistatic contact problem with Coulomb friction in linear elasticity (Signorini–Coulomb problem) is unraveled and sharp existence results are proved for the most general two-dimensional problem with arbitrary geometry and elasticity modulus tensor. The problem is reduced to a variational inequality involving a nonlinear operator which handles both elasticity and friction. This operator is proved to fall into the class of the so-called Leray–Lions operators, so that a result of Brézis can be invoked to solve the variational inequality. It turns out that one property in the definition of Leray–Lions operators is difficult to check and requires proving a new fine property of the linear elastic Neumann-to-Dirichlet operator. This fine property is only established in the case of the two-dimensional problem, limiting currently our existence result to that case. In the case of isotropic elasticity, either homogeneous or heterogeneous, the existence of solutions to the Signorini–Coulomb problem is proved for arbitrarily large friction coefficient. In the case of anisotropic elasticity, an example of nonexistence of a solution for large friction coefficient is exhibited and the existence of solutions is proved under an optimal condition for the friction coefficient. [ABSTRACT FROM AUTHOR]

When a charismatic Sri Lankan holy man moved to Philadelphia in the early 1970s and set up a new branch of his movement, he began a process of adaptation to the North American context that has continued since his death. Within the new Bawa Muhaiyaddeen Fellowship, adherents in favor of a more liberal style of worship have clashed with a stricter official interpretation of the founder's views on Islamic requirements, while relations with the original Sri Lankan organization have also experienced frictions. The history of the fellowship is a case study in how the globalization of religion results in heterogeneous versions of a common faith. [ABSTRACT FROM AUTHOR]

The vertical bearing capacity of the suction caissons is vital to the safety of marine jacket foundations. The sand friction angle is a key parameter for calculating the vertical bearing capacity. The sand friction angle is state-dependent, which is affected by the compact state and stress state. However, this effect is neglected in the current study, resulting in deviations in the calculation results of the vertical bearing capacity. Therefore, a novel method is preliminarily proposed to account for this impact while evaluating the vertical bearing capacity of suction foundations. First, a new friction angle is expressed as a function of relative density and soil depth, which differs significantly from the commonly used constant friction angle. The state-dependent sand friction angle is available. Then, the general and simplified vertical bearing capacity formulas are clarified. Four key parameters in the former and a new first-order coefficient in the latter are identified. The calculation procedure based on the new friction angle is also specified. Finally, combined with model tests, a comparison study is carried out. The results show that the calculation results using the new friction angle are more accurate and practical. This study can provide a reference for the foundation design. [ABSTRACT FROM AUTHOR]

The pullout capacity of horizontal anchor plates plays a crucial role in ensuring the stability and performance of various structures subjected to uplift or lateral loading. This paper presents an investigation into the pullout capacity of horizontal anchor plates using the method of stress characteristics. The method offers a simplified analytical approach that allows for quick estimations and insights into the stress distribution and failure mechanism of anchor plates. The study focuses on circular anchor plates with varying embedment ratios, considering different soil friction angles. Through computational analyses and the generation of characteristic grids, the behavior and stress distribution of anchor plates are examined. The results are compared with several experimental data from the literature to validate the applicability of the method. The findings provide valuable insights into the influence of embedment ratios and soil friction angles on the pullout capacity of horizontal anchor plates. This research contributes to the understanding of anchor plate behavior and offers a practical tool for assessing their performance in geotechnical engineering applications. [ABSTRACT FROM AUTHOR]

This paper focuses on an innovative foundation type of monopile-friction wheel composite foundations, which aim to enhance the loading performance of offshore wind turbines (OWTs) while mitigating the negative impact of local scouring. The study utilizes numerical simulations to investigate the morphology of local scouring under unidirectional flow. Furthermore, the finite element method is employed to quantify the lateral bearing behavior, considering different scouring parameters, loading point heights, and pre-torsional loads. On this basis, the load bearing ratio of each part of the composite foundation under different scour conditions is also obtained. The results reveal that the horizontal bearing characteristics are significantly influenced by different scour parameters, loading point heights and pre-torsional loads. The local scouring can reduce the bearing capacity by about 38%, with scouring depth having the greatest effect, followed by the scouring angle and extent respectively. Moreover, as the loading point height and pre-torsional load increase, the lateral bearing behavior of composite foundations decreases. Notably, the friction wheel contributes more than 40% to the overall bearing capacity, underscoring its importance. The results provide valuable insights into further understanding the bearing behavior of the composite foundation and its potential engineering applications. [ABSTRACT FROM AUTHOR]