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Purpose: The utilization of intra-aortic balloon pump (IABP) and Impella has been suggested as means of left ventricular unloading in veno-arterial extracorporeal membrane oxygenation (VA-ECMO) patients. This study aimed to assess the local hemodynamic alterations in VA-ECMO patients through simulation analyses. Methods: In this study, a 0D-3D multiscale model was developed, wherein resistance conditions were employed to define the flow-pressure relationship. An idealized model was employed for the aorta, and simulations were conducted to contrast the hemodynamics supported by two configurations: VA-ECMO combined with IABP, and VA-ECMO combined with Impella. Results: In relation to VA-ECMO alone, the combination treatment had the following differences: (1) overall mean mass flow rate increased significantly when combined with Impella and did not change significantly when combined with IABP. Blood flow pulsatility was the strongest in ECMO + IABP, and blood flow pulsatility was significantly suppressed in ECMO + Impella; (2) for all arterial inlets, HI was decreased with ECMO + Impella and increased with ECMO + IABP; (3) the flow field did not change much with ECMO + IABP, with better blood flow compliance, whereas the flow field was relatively more chaotic and disorganized with ECMO + Impella; (4) the difference between shear stress values in ECMO + IABP and ECMO alone was small, and ECMO + Impella (P6) had the largest shear stress values. Conclusions: Variances in hemodynamic efficacy between VA-ECMO combined with IABP and VA-ECMO combined with Impella may underlie divergent prognoses and complications. The approach to ventricular unloading during ECMO and the degree of support should be meticulously tailored to individual patient conditions, as they represent pivotal factors influencing vascular complications. [ABSTRACT FROM AUTHOR]

This paper provides a new open-source software, named BioReactPy, for simulation of microbial-mediated coupled processes of flow and reactive transport in porous media. The software is based on the micro-continuum approach, and geochemistry is handled in a fully coupled manner with biomass-nutrient growth treated with Monod equation in a single integrated framework, without dependencies on third party packages. The distinguishing features of the software, its design principles, and formulation of multiphysics problems and discretizations are discussed. Validation of the Python implementation using several established benchmarks for flow, reactive transport, and biomass growth is presented. The flexibility of the framework is then illustrated by simulations of highly non-linearly coupled flow and microbial reactive transport at conditions relevant to carbon mineralization for CO2 storage. All results can be reproduced by openly available simulation scripts.

Electrocatalytic hydrogen evolution reaction (HER) is critical for green hydrogen generation and exhibits distinct pH-dependent kinetics that have been elusive to understand. A molecular-level understanding of the electrochemical interfaces is essential for developing more efficient electrochemical processes. Here we exploit an exclusively surface-specific electrical transport spectroscopy (ETS) approach to probe the Pt-surface water protonation status and experimentally determine the surface hydronium pKa [Formula: see text] 4.3. Quantum mechanics (QM) and reactive dynamics using a reactive force field (ReaxFF) molecular dynamics (RMD) calculations confirm the enrichment of hydroniums (H3O[Formula: see text]) near Pt surface and predict a surface hydronium pKa of 2.5 to 4.4, corroborating the experimental results. Importantly, the observed Pt-surface hydronium pKa correlates well with the pH-dependent HER kinetics, with the protonated surface state at lower pH favoring fast Tafel kinetics with a Tafel slope of 30 mV per decade and the deprotonated surface state at higher pH following Volmer-step limited kinetics with a much higher Tafel slope of 120 mV per decade, offering a robust and precise interpretation of the pH-dependent HER kinetics. These insights may help design improved electrocatalysts for renewable energy conversion.

Cement fractures represent preferential leakage pathways in abandoned wells upon exposure to a CO2-rich fluid. Understanding fracture alteration resulting from geochemical reactions is critical for assessing well integrity in CO2 storage. This paper describes a mathematical model used to investigate the physical and the chemical changes in cement properties when CO2-saturated water is injected into a wellbore. This study examines the flow of a solution of CO2-saturated water in a two-dimensional fractured cement. In this approach, a micro-continuum equation based on the Darcy–Brinkman–Stokes (DBS) equation is used as the momentum balance equation; in addition, reactive transport equations are used to study the coupled processes of reactant transport and geochemical reactions, and the model for cement porosity alteration and fracture enhancement. This paper focuses on the effects of cement porosity, fracture aperture size, and surface roughness. Mineral dissolution and precipitation mechanisms are also considered. Our simulations show that smaller initial fracture apertures tend to a high mineral precipitation self-sealing. However, a complete sealing of the fracture is not observed due to the continuous flow of CO2-saturated water. The calcite precipitation mechanism of a rough fracture (random zigzag shape) differs from that of a smooth/flat fracture surface. [ABSTRACT FROM AUTHOR]

Nanofluidics research has achieved a significant growth over the past few years. New phenomena of nanoscaled fluid flows are being reported continuously, such as altered liquid properties, fast flows, and ion rectification, which attract tremendous research interests in many fields, such as membrane science, biological nanochips, and energy conventions. Multiscale simulations, covering quantum mechanics, molecular mechanics, coarse‐grained particle dynamics (mesoscale), and continuum mechanics, have shown their great advantages in studying the new frontier of nanofluidics in academia and industry, which is in range of 1–1000 nm scale. These simulations provide the opportunity to visualize the nanofluidics applications existed in the minds of scientists and then guide experimental design to realize the potential of nanofluidics applications in industrial. In this article, we attempt to give a comprehensive review of nanofluidics from the aspect of multiscale simulations. The methodology and role of various simulation methods used in the investigation of nanofluidics are presented. The properties and characteristics of nanofluidics are summarized. The applications of nanofluidics in recent years are emphasized. And then the development of simulation methods and the application of nanofluidics are also prospected. This article is categorized under:Molecular and Statistical Mechanics > Molecular Dynamics and Monte‐Carlo MethodsSoftware > Simulation Methods [ABSTRACT FROM AUTHOR]

TNFα is a highly pleiotropic cytokine inducing inflammatory signaling pathways. It is initially presented on plasma membrane of cells (mTNFα), and also exists in a soluble variant (sTNFα) after cleavage. The ligand is shared by two structurally similar receptors, TNFR1 and TNFR2. Interestingly, while sTNFα preferentially stimulates TNFR1, TNFR2 signaling can only be activated by mTNFα. How can two similar receptors respond to the same ligand in such a different way? We employed computational simulations in multiple scales to address this question. We found that both mTNFα and sTNFα can trigger the clustering of TNFR1. The size of clusters induced by sTNFα is constantly larger than the clusters induced by mTNFα. The systems of TNFR2, on the other hand, show very different behaviors. Only when the interactions between TNFR2 are very weak, mTNFα can trigger the receptors to form very large clusters. Given the same weak binding affinity, only small oligomers were obtained in the system of sTNFα. Considering that TNF-mediated signaling is modulated by the ligand-induced clustering of receptors on cell surface, our study provided the mechanistic foundation to the phenomenon that different isoforms of the ligand can lead to highly distinctive signaling patterns for its receptors. [ABSTRACT FROM AUTHOR]

Glassy polymers are often used for gas separations because of their high selectivity. Although the dual-mode permeation model correctly fits their sorption and permeation isotherms, its physical interpretation is disputed, and it does not describe permeation far from steady state, a condition expected when separations involve intermittent renewable energy sources. To develop a more comprehensive permeation model, we combine experiment, molecular dynamics, and multiscale reaction–diffusion modeling to characterize the time-dependent permeation of N2 and CO2 through a glassy poly(dimethyl phenylene oxide) membrane, a model system. Simulations of experimental time-dependent permeation data for both gases in the presteady-state and steady-state regimes show that both single- and dual-mode reaction–diffusion models reproduce the experimental observations, and that sorbed gas concentrations lag the external pressure rise. The results point to environment-sensitive diffusion coefficients as a vital characteristic of transport in glassy polymers.

A ceramic–ceramic (CERCER) fuel with minor actinide-enriched ceramic fuel particles dispersed in a MgO ceramic matrix is chosen as a promising composite target for accelerator-driven systems (ADS). Fission swelling is a complex irradiation-induced phenomenon that involves recrystallization, resolution, and hydrostatic pressure under extreme conditions of high temperature and significant fission flux. In this study, a multiscale computational framework was developed to integrate simulations of continuum-scale thermo-mechanical behavior in the CERCER composite with a grain-scale hydrostatic pressure-dependent fission gas swelling model. Hydrostatic pressure-dependent fission welling is taken into account in the stress update algorithms for U O 2 particles. Accordingly, we programmed the user subroutines to define the thermo-mechanical constitutive relations in the finite element simulations. The obtained results indicate that (1) the proposed method accurately predicts the swelling deformation at various burnup levels while taking into account hydrostatic pressure and (2) prior to recrystallization, the particle swelling is primarily influenced by temperature variation, whereas after recrystallization, the presence of hydrostatic pressure favorably suppresses the swelling deformation. This work effectively captures the swelling behavior influenced by hydrostatic pressure within the dispersed-type CERCER composite fuel in ADSs. [ABSTRACT FROM AUTHOR]

Microstructural atomic defects, including voids, cleavage, and inclusions, are commonly observed in alumina materials, and their impact on mechanical properties, such as fracture stress and toughness, is significant. In this paper, we introduce novel alumina models that incorporate experimentally observed void features. An atomic model is established to study the effects of micro-structural void features on fracture properties and atomic structure changes using molecular dynamics simulations. The electron backscatter diffraction and scanning electronic microscopy analysis of experimental samples are used to evaluate microstructural features that are used as inputs to the simulations (e.g., void aspect ratio, void angle). We apply an innovative Atomistic-to-Continuum (ATC) method based on Riemann sums to bridge atomic and continuum mechanics theories, evaluating the resistance of materials with atomic defects to crack propagation. The results show the greatest effects of pore angles on weakening mechanical properties such as peak strength and fracture energy density. The accuracy and efficiency of the ATC method in evaluating stress intensity factors are used to calculate the mechanical responses. Additionally, we establish a multiple layer perceptron neural network to evaluate the complex relationship between void features (aspect ratio, pore angle, relative distance) and typical fracture properties (fracture stress, critical stress intensity factor). A meta-analysis of these results from both machine learning methods and molecular dynamics simulations reveals the significant impact of each void feature on the sensitivity of typical fracture properties (peak strength, critical stress intensity factor at peak strength) and highlights the critical role of aspect ratio on fracture properties. [Display omitted] • Experimentally observed voids are characterized for atomic alumina. • The atomistic to continuum method bridges different scaled mechanics. • Artificial neural network bridges void features with fracture properties. • Meta-analysis reveals the void aspect ratio impact on fracture. [ABSTRACT FROM AUTHOR]

Cement fractures represent preferential leakage pathways in abandoned wells upon exposure to a CO2-rich fluid. Understanding fracture alteration resulting from geochemical reactions is critical for assessing well integrity in CO2 storage. This paper describes a mathematical model used to investigate the physical and the chemical changes in cement properties when CO2-saturated water is injected into a wellbore. This study examines the flow of a solution of CO2-saturated water in a two-dimensional fractured cement. In this approach, a micro-continuum equation based on the Darcy–Brinkman–Stokes (DBS) equation is used as the momentum balance equation; in addition, reactive transport equations are used to study the coupled processes of reactant transport and geochemical reactions, and the model for cement porosity alteration and fracture enhancement. This paper focuses on the effects of cement porosity, fracture aperture size, and surface roughness. Mineral dissolution and precipitation mechanisms are also considered. Our simulations show that smaller initial fracture apertures tend to a high mineral precipitation self-sealing. However, a complete sealing of the fracture is not observed due to the continuous flow of CO2-saturated water. The calcite precipitation mechanism of a rough fracture (random zigzag shape) differs from that of a smooth/flat fracture surface.

A multiscale simulation method is used to calculate the rheological properties of entangled Nylon 6 melts, including the stress relaxation modulus, storage and loss moduli, and the melt viscosity. The three‐level multiscale approach includes all‐atom, coarse‐grained and slip‐spring models, each operating at different levels of resolution and encompassing a wide range of length scales and over nine orders of magnitude in time. These models are unified by matching the polymer chain structure and dynamics as well as the stress relaxation, and together predict the rheological master curves at various temperatures using time–temperature superposition. The calculated viscosity agrees reasonably with experiment. The effect of polydispersity on rheology is also studied by simulating a polydisperse melt with chain lengths follow the Schulz‐Zimm distribution. Under the same weight‐average molecular weight, the polydisperse melt shows faster stress relaxation and lower viscosity compared to the monodisperse melt. For polymers that undergo rapid degradation at elevated temperatures, such as Nylon, the proposed approach offers a useful means to investigate rheology over a wide range of conditions. Importantly, the approach is fully predictive in that calculations of rheology are generated without relying on experimental information, and it therefore offers potential for design of polymeric materials on the basis of purely molecular models. [ABSTRACT FROM AUTHOR]

Polydimethylsiloxane/silica (PDMS/SiO2) particle-reinforced nanocomposites prepared at the present study are typical viscoelastic materials. Due to the high surface-to-volume ratio of the SiO2 nanoparticles, the interface effects on the overall properties of the nanocomposites cannot be ignored. In order to investigate the interface effects on the viscoelastic properties of the nanocomposites, a multiscale model is established in the present study, combining the molecular dynamics (MD) model of the interface at the nanoscale and the unit cell model of the nanocomposites at the mesoscale. In the MD model of the interface, the viscoelastic properties of the interphase region influenced by the interface are found to be different from that of the pure PDMS matrix and the bulk SiO2. Because the polymer chains subject to different restrictions existing in the interphase region, this region can possess high stiffness and damping properties simultaneously. The interphase parameters can be determined by the inverse multiscale simulation method, taking advantage of both the numerical model and the experimental results. Due to the interface effects, as demonstrated by the unit cell model, the dynamic shear moduli of the nanocomposites can be simultaneously improved by several times to an order of magnitude higher than that of the matrix, in consistent with experimental results. Thus, the mechanism of the interface effects enhancing the viscoelastic properties of the PDMS/SiO2 nanocomposites can be revealed in the present study, which can be useful for the design of viscoelastic nanocomposites with high stiffness and damping properties. [ABSTRACT FROM AUTHOR]

Ceramic aerogels prepared by the route of polymer-derived ceramics (PDCs) have been of significant attention in high-temperature insulation. However, the application of ceramic aerogels was seriously confined due to the structural damage and shrinkage cracking of ceramic precursors during pyrolysis. In this investigation, precursor ceramic microsphere aerogels with outstanding antishrinkage properties were prepared by storing strain in curled molecular chains and using polysilazane (PSZ) as the precursor. Meanwhile, precursor ceramic microsphere aerogels with different curled molecular chain structures were prepared by modulating solvent interactions and cross-linked structures. Different curled molecular chain structures were formed, and the impact on the antishrinkage properties of precursor aerogels was analyzed. The shrinkage resistance, thermal insulation, and mechanical properties of the prepared aerogels were tested and compared. Furthermore, the mechanism of the impact of different curled molecular chain structures on thermal insulation and mechanical properties was investigated through multiscale simulations combined with fractal theory. The thermal and stress transfer at the interfaces of different microsphere skeleton structures and the mechanisms were investigated. An idea for solving the problem of pyrolytic shrinkage in the preparation of ceramic aerogels was provided in this investigation. In addition, insights into the influence of the microsphere skeleton structure on the thermal and mechanical properties of ceramic aerogels were provided.

Multiscale coarse-grained (CG) models are expected to play the critical roles in molecular simulations of complex polymers. However, this poses a great challenge for accurately simulating their thermomechanical properties, for which excellent representability and transferability are required for the CG potentials. In this work, virtual sites and elastic network bonds are introduced to improve the structural and volumetric property–based CG models including explicit electrostatic interactions, which is exemplarily applied to the iso- and syndio-tactic poly(methyl methacrylate). A variety of thermomechanical properties of the two stereoregular polymer bulks are reasonably reproduced by the extensive molecular dynamics simulations with the so-parameterized CG potentials. In particular, the attractive nature of electrostatic interactions and tacticity effects on glass transition temperatures (Tg) are well captured. Furthermore, stronger electrostatic interactions lead to higher mass density and bulk modulus, and their effects on Young's modulus, Poisson's ratio, and shear modulus depend upon the chain tacticity. It is also demonstrated that all these elastic constants can be effectively modulated by imposing external electric field. The proposed multiscale scheme can be very valuable to molecular designs of polar polymer materials. [ABSTRACT FROM AUTHOR]

The distinct physical properties of hybrid organic-inorganic materials can lead to unexpected nonequilibrium phenomena that are difficult to characterize due to the broad range of length and time scales involved. For instance, mixed halide hybrid perovskites are promising materials for optoelectronics, yet bulk measurements suggest the halides reversibly phase separate upon photoexcitation. By combining nanoscale imaging and multiscale modeling, we find that the nature of halide demixing in these materials is distinct from macroscopic phase separation. We propose that the localized strain induced by a single photoexcited charge interacting with the soft, ionic lattice is sufficient to promote halide phase separation and nucleate a light-stabilized, low-bandgap, ∼8 nm iodide-rich cluster. The limited extent of this polaron is essential to promote demixing because by contrast bulk strain would simply be relaxed. Photoinduced phase separation is therefore a consequence of the unique electromechanical properties of this hybrid class of materials. Exploiting photoinduced phase separation and other nonequilibrium phenomena in hybrid materials more generally could expand applications in sensing, switching, memory, and energy storage.

A ceramic–ceramic (CERCER) fuel with minor actinide-enriched ceramic fuel particles dispersed in a MgO ceramic matrix is chosen as a promising composite target for accelerator-driven systems (ADS). Fission swelling is a complex irradiation-induced phenomenon that involves recrystallization, resolution, and hydrostatic pressure under extreme conditions of high temperature and significant fission flux. In this study, a multiscale computational framework was developed to integrate simulations of continuum-scale thermo-mechanical behavior in the CERCER composite with a grain-scale hydrostatic pressure-dependent fission gas swelling model. Hydrostatic pressure-dependent fission welling is taken into account in the stress update algorithms for UO2 particles. Accordingly, we programmed the user subroutines to define the thermo-mechanical constitutive relations in the finite element simulations. The obtained results indicate that (1) the proposed method accurately predicts the swelling deformation at various burnup levels while taking into account hydrostatic pressure and (2) prior to recrystallization, the particle swelling is primarily influenced by temperature variation, whereas after recrystallization, the presence of hydrostatic pressure favorably suppresses the swelling deformation. This work effectively captures the swelling behavior influenced by hydrostatic pressure within the dispersed-type CERCER composite fuel in ADSs.

Electric-field control of magnetization reversal is promising for low-power spintronics. Here in a magnet/insulator nanoheterostructure which is the fundamental unit of magnetic tunneling junction in spintronics, we demonstrate the electric field induced 180$$^ \circ $$ magnetization switching through a multiscale study combining first-principles calculations and finite-temperature magnetization dynamics. In the model nanoheterostructure MgO/Fe/Cu with insulator MgO, soft nanomagnet Fe and capping layer Cu, through first-principles calculations we find its magnetocrystalline anisotropy linearly varying with the electric field. Using finite-temperature magnetization dynamics which is informed by the first-principles results, we disclose that a room-temperature 180$$^ \circ $$ magnetization switching with switching probability higher than 90% is achievable by controlling the electric-field pulse and the nanoheterostructure size. The 180$$^ \circ $$ switching could be fast realized within 5 ns. This study is useful for the design of low-power, fast, and miniaturized nanoscale electric-field-controlled spintronics.

The exchange is critical for designing high-performance Nd–Fe–B permanent magnets. Here we demonstrate through multiscale simulations that the exchange in Nd–Fe–B magnets, including bulk exchange stiffness (Ae) in Nd2Fe14B phase and interface exchange coupling strength ( $J_{\rm int} $) between Nd2Fe14B and grain boundary (GB), is strongly anisotropic. Ae is larger along crystallographic a/b axis than along c axis. Even when the GB FexNd1–x has the same composition, $J_{\rm int} $ for (100) interface is much higher than that for (001) interface. The discovered anisotropic exchange is shown to have profound influence on the coercivity. These findings enable more freedom in designing Nd–Fe–B magnets by tuning exchange.

Zeolites, an important class of 3-dimensional nanoporous materials, have been widely explored for a variety of applications including gas storage, separations, and catalysis. As the properties of these aluminosilicate materials depend on a number of factors (e.g., framework topology, Si/Al ratio, extra-framework cations etc.), detailed experiments (e.g., catalytic properties, adsorption capacities etc.) are often limited to only a handful of materials. Computational methods have played an important role in (1) providing molecular level insights to rationalize experimental observations, and (2) screening large libraries of zeolites to identify promising candidates for experimental synthesis and validation. Different levels of theory and computational chemistry codes are necessary to describe the range of relevant phenomena such as adsorption (e.g., grand canonical Monte Carlo), diffusion (e.g., molecular dynamics), and chemical reactions (e.g., density functional theory). Manipulation of atomic structures, handling of input files, and developing robust workflows becomes quite cumbersome. To mitigate these challenges, we describe the development of the Multiscale Atomic Zeolite Simulation Environment (MAZE) – a Python package that simplifies zeolite-specific calculation workflows by providing a user-friendly interface for systematically manipulating zeolite structures.

Emerging machine learning (ML) methods are widely applied in chemistry and materials science studies and have led to a focus on data‐driven research. This Minireview summarizes the application of ML to rechargeable batteries, from the microscale to the macroscale. Specifically, ML offers a strategy to explore new functionals for density functional theory calculations and new potentials for molecular dynamics simulations, which are expected to significantly enhance the challenging descriptions of interfaces and amorphous structures. ML also possesses a great potential to mine and unveil valuable information from both experimental and theoretical datasets. A quantitative "structure–function" correlation can thus be established, which can be used to predict the ionic conductivity of solids as well as the battery lifespan. ML also exhibits great advantages in strategy optimization, such as fast‐charge procedures. The future combination of multiscale simulations, experiments, and ML is also discussed and the role of humans in data‐driven research is highlighted. [ABSTRACT FROM AUTHOR]

A multiscale simulation strategy was proposed to study the curing reaction on the network formation and corresponding mechanical properties of a bio-based epoxy resin composite. The crosslinking process of the system to form an epoxy network structure was reproduced on the mesoscopic scale by the dissipative particle dynamics simulation coupled with a curing reaction model. The density functional theory (DFT)-based method, IRC and relaxed potential energy surface scanning calculations were combined with the reverse mapping operations in order to improve the overall quality the reverse mapped structures. Finally, molecular dynamics simulations were performed on the atomistic level to analyze the mechanical properties, the volume shrinkage and the glass transition of the bio-based epoxy resin system, etc. This multiscale simulation strategy can provide as a possible investigation scheme for the subsequent improvement and design of bio-based epoxy resin composite materials.

Macrosegregation is the key issue in the solidification field. Oxygen and its inclusions play the important role in driving the melt flow and the resulting macrosegregation in steel. Here, to reveal the inducing mechanism and quantitative model of oxygen content in real industrial steel ingots, we demonstrate for the first time that there exists the critical oxygen content in triggering the formation of channel-type segregation, the most undesirable macrosegregation type in steel. Our multiscale simulations from density functional theory calculations to multiphase/multicomponent macromodel, clarify the quantitative conditions initializing channel-type segregation and reveal two typical growth modes via oxide flotation. The oxygen content model and criterion to induce the channel onset is built accordingly, which are validated by the numerous full ingot dissections and experimental characterizations including the in situ electrolysis of inclusions, X-ray microtomography, scanning electron microscope, large-scale measurement system of inclusions and chemical analysis. With oxygen controlled below this critical value of 0.0008 wt%, channel disappears. This study quantitatively uncovers the novel role of oxygen in steel, changes the traditional sole concept of cleanliness, and highlights an innovative and controlling-effective route to fabricate homogenized steel.

Biological membranes exhibit diversity in their shapes and complexity in chemical compositions that are linked to many cellular functions. These two central features of biomembranes have been the subject of numerous simulation studies, using a diverse range of computational techniques. Currently, the field is able to capture this complexity at increasing levels of realism and connect the microscopic view on protein–lipid interactions to cellular morphologies at the level of entire organelles. Here we highlight recent advances in this topic, identify current bottlenecks, and sketch possible ways ahead. [ABSTRACT FROM AUTHOR]

Electrical nerve fiber stimulation is a technique widely used in prosthetics and rehabilitation, and its study from a computational point of view can be a useful instrument to support experimental tests. In the last years, there was an increasing interest in computational modeling of neural cells and numerical simulations on nerve fibers stimulation because of its usefulness in forecasting the effect of electrical current stimuli delivered to tissues through implanted electrodes, in the design of optimal stimulus waveforms based on the specific application (i.e., inducing limb movements, sensory feedback or physiological function restoring), and in the evaluation of the current stimuli properties according to the characteristics of the nerves surrounding tissue. Therefore, a review study on the main modeling and computational frameworks adopted to investigate peripheral nerve stimulation is an important instrument to support and drive future research works. To this aim, this paper deals with mathematical models of neural cells with a detailed description of ion channels and numerical simulations using finite element methods to describe the dynamics of electrical stimulation by implanted electrodes in peripheral nerve fibers. In particular, we evaluate different nerve cell models considering different ion channels present in neurons and provide a guideline on multiscale numerical simulations of electrical nerve fibers stimulation. [ABSTRACT FROM AUTHOR]

This study investigates the mechanisms behind the great mechanical properties observed at room temperature for a dual-phase Ti-6Al-2Sn-4Zr-2Mo-Si titanium alloy with equiaxed (α + β) microstructures. More precisely, analyzing the material deformation modes and the possible effects of β fraction and grain size was done to better understand such micromechanisms. With this idea in mind, uniaxial tensile deformation tests were performed at room temperature, and the resulting mechanical behaviors were analyzed. It was observed that increasing β fraction would enhance the overall ductility and work hardening while conversely decreasing the material resistance. Additionally, the material strengthening due to grain size effect, quantified by the Hall-Petch parameter, was also found to be dependent on β fraction. Slip trace analysis was conducted to understand the effects of grain size and β fraction on the activation of the basal , prismatic , and pyramidal slip systems and their critical resolved shear stress (CRSS) ratios were established. The qualitative study of CRSS ratios revealed that at smaller grain sizes, the basal slip systems were dominant (e.g. basal/prismatic CRSS ratio of 0.86 for d=2.98 µm) whereas the prismatic slip systems were prevalent and more easily activated for coarser grains (e.g. basal/prismatic CRSS ratio of 1.19 for d=4.21 µm). Such CRSS ratios were then used to identify the material parameters of a self-consistent multiscale model employed to reproduce the tensile behaviors. For a more quantitative analysis, the CRSS values were evaluated and correlated to grain sizes with Hall-Petch relations. Clear correlations regarding grain size and β fraction were found for the CRSS of prismatic and pyramidal systems. However, special attention was given to the ambiguous results regarding basal slip systems because of the potential manifestation of the compatibility stresses and grain boundary sliding mechanisms due to the higher density of grain boundaries at small grain sizes. • Hall-Petch phenomenon (grain size effect) is found to be dependent on β fraction. • CRSS ratios change with changing grain size in the studied Ti-6242S alloy. • Grain boundaries affect CRSS evolution, especially in fined-grained conditions. • Prismatic & pyramidal CRSS values were related to grain size & β fraction. • Basal CRSS values do not correlate with grain size. [ABSTRACT FROM AUTHOR]

• Novel coiled hollow fiber (CHF) module is proposed for MD process. • CHF module is investigated in cross-flow and localized heating (LH) modes. • Mitigation of temperature polarization due to the normal feed direction to the fiber. • Higher flux and lower energy than the conventional design are achieved by CHF. • CHF with LH mode is the most performant and energy-efficient module for MD scale-up. Membrane distillation (MD) scale-up is challenged by ineffective heat recovery and the temperature polarization effect. Direct contact membrane distillation (DCMD) modules suffer high thermal conduction losses due to feed flow direction along the length of the membrane, resulting in low thermal efficiency. We propose a novel module design named coiled hollow fiber (CHF) to decouple the flow direction from the membrane surface in hollow fiber (HF) DCMD. Experimental and computational analyses were employed to compare the performance of CHF and the conventional design. The CHF module design successfully mitigates the TP effect in HF DCMD, increasing the flux by 148 % and 163 % in cross-flow and localized heating (LH) modes, respectively. Moreover, CHF operated in LH mode exhibits the lowest energy consumption of all configurations (81 % decrease) compared to the conventional design. This novel module design represents a new pathway for efficient and highly performing DCMD module. [Display omitted] [ABSTRACT FROM AUTHOR]

The solute strengthening caused by the interaction between dislocations and solutes in random solid solution alloys has already been investigated widely provided that the solutes outside the dislocation core interact through nominally elastic interactions. However, the topological variation of dislocation core due to the solute segregation can influence the strengthening of system. We investigate the dislocation core reconstruction with solute C and Nb and their effects on dislocation glide in γ -TiAl by multiscale QM/MM scheme due to the long-range elastic field of a dislocation. The solutes doping in dislocation core region can influence the core energy and eventually cause a violation of Frank's rule. The contribution analysis of lattice distortion and chemical effect between dislocations and solutes is further investigated. The energy barriers of constriction and transition state in pure γ -TiAl and under solutes environment in the process of external stress reveal electronically the effects of alloying elements and heterogeneous mechanisms on cross-slip process. The carbon diffusion along and across dislocation core by the CI-NEB method are also investigated. [Display omitted] • Dislocation core reconstruction by C/Nb in the long-range elastic field of it. • Strain energy separated into lattice distortion and chemical effect contributions. • Dislocation mobility with C/Nb in its core under stress and the C diffusion in it. [ABSTRACT FROM AUTHOR]

We present the VECMA toolkit (VECMAtk), a flexible software environment for single and multiscale simulations that introduces directly applicable and reusable procedures for verification, validation (V&V), sensitivity analysis (SA) and uncertainty quantication (UQ). It enables users to verify key aspects of their applications, systematically compare and validate the simulation outputs against observational or benchmark data, and run simulations conveniently on any platform from the desktop to current multi-petascale computers. In this sequel to our paper on VECMAtk which we presented last year [1] we focus on a range of functional and performance improvements that we have introduced, cover newly introduced components, and applications examples from seven different domains such as conflict modelling and environmental sciences. We also present several implemented patterns for UQ/SA and V&V, and guide the reader through one example concerning COVID-19 modelling in detail. This article is part of the theme issue 'Reliability and reproducibility in computational science: implementing verification, validation and uncertainty quantification in silico'. [ABSTRACT FROM AUTHOR]

This review addresses resistive switching devices operating according to the bipolar valence change mechanism (VCM), which has become a major trend in electronic materials and devices over the last decade due to its high potential for non-volatile memories and future neuromorphic computing. We will provide detailed insights into the status of understanding of these devices as a fundament for their use in the different fields of application. The review covers the microscopic physics of memristive states and the switching kinetics of VCM devices. It is shown that the switching of all variants of VCM cells relies on the movement of mobile donor ions, which are typically oxygen vacancies or cation interstitials. VCM cells consist of three parts: an electronically active electrode (AE), often a metal with a high work function, in front of which the switching occurs, a mixed ionic-electronic conducting (MIEC) layer consisting of a nanometer-scale metal oxide or a stack of different metal oxides, and an ohmic counter electrode (OE). After an introduction to definitions and classification, the fundamentals of solid-state physics and chemistry associated with VCM cells are described, including redox processes and the role of electrodes. The microscopic changes induced by electroforming, a process often required prior to resistive switching, are described in terms of electronic initialization and subsequent changes in chemistry, structure, and conductivity. The switching process is discussed in terms of switching polarity, geometry of the switching region, and spectroscopic detection of the valence changes. Emphasis is placed on the extreme nonlinearity of switching kinetics described by physics-based multiscale modeling, ranging from ab initio methods to kinetic Monte Carlo and finite element models to compact models that can be used in circuit simulators. The review concludes with a treatment of the highly relevant reliability issues and a description of the failure mechanisms, including mutual trade-offs. [ABSTRACT FROM AUTHOR]

Electric-field control of magnetization reversal is promising for low-power spintronics. Here in a magnet/insulator nanoheterostructure which is the fundamental unit of magnetic tunneling junction in spintronics, we demonstrate the electric field induced 180 ∘ magnetization switching through a multiscale study combining first-principles calculations and finite-temperature magnetization dynamics. In the model nanoheterostructure MgO/Fe/Cu with insulator MgO, soft nanomagnet Fe and capping layer Cu, through first-principles calculations we find its magnetocrystalline anisotropy linearly varying with the electric field. Using finite-temperature magnetization dynamics which is informed by the first-principles results, we disclose that a room-temperature 180 ∘ magnetization switching with switching probability higher than 90% is achievable by controlling the electric-field pulse and the nanoheterostructure size. The 180 ∘ switching could be fast realized within 5 ns. This study is useful for the design of low-power, fast, and miniaturized nanoscale electric-field-controlled spintronics. [ABSTRACT FROM AUTHOR]

Multiscale simulation study results of multilayer structures consisting of graphene sheets with embedded Pt nanoparticles is reported. Density functional theory is used to understand the energetics of Pt–graphene interfaces and provide reference data for the parameterization of a Pt–graphene interaction potential. Molecular dynamics simulations then provide the conformation and energetics of graphene sheets with embedded Pt nanoparticles of varying density, form, and size. These results are interpreted using a continuum mechanical model of sheet deformation, and serve to parameterize a meso‐scale Monte Carlo model to investigate the question under which conditions the free volume around the Pt nanoparticles forms a percolating cluster, such that the structures can be used in catalytic applications. This article is concluded with a discussion of potential applications of such multilayer structures. [ABSTRACT FROM AUTHOR]

Validation, verification, and uncertainty quantification (VVUQ) of simulation workflows are essential for building trust in simulation results, and their increased use in decision‐making processes. The EasyVVUQ Python library is designed to facilitate implementation of advanced VVUQ techniques in new or existing workflows, with a particular focus on high‐performance computing, middleware agnosticism, and multiscale modeling. Here, the application of EasyVVUQ to five very diverse application areas is demonstrated: materials properties, ocean circulation modeling, fusion reactors, forced human migration, and urban air quality prediction. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations have been performed with chemically realistic coarse-grained potentials to assess the effects of molecular weight on the glass transition temperatures (Tg) of single-chain particle of poly(ethylene oxide) in a vacuum. It is found that all the long isolated chains form impact globule like configurations, and higher molecular weight and lower temperature lead to more perfect sphericity. With increasing molecular weight, the simulated Tg of the isolated chain tends to increase whereas the Tg of the bulk undergoes a slight change. The confinement effects are associated with localisation of chain ends at the surface and specific surface areas. More importantly, the Tg shift can be quantified by the solubility parameter that includes the contribution of conformational change. As compared to the conventional definition that only sums intermolecular interactions, such solubility parameter is a better metric in simulations to explain the confinement effects since it does not depend upon the degree of equilibration as the Tg. These results can be quite valuable to clarifying glass transition behaviour of polymers films. [ABSTRACT FROM AUTHOR]

An amorphous/crystalline metallic composite (A/C-MC) integrates metallic glass with crystalline metals in one system. The amorphous-crystalline interface (ACI) in A/C-MCs under deformation absorbs dislocations and may fundamentally change the dilemma that the strength comes at the expense of the ductility of a material. However, the development of such materials is still at a trial and error stage due to the lack of a clear-cut understanding on how the amorphous component become instable when a dislocation-mediated plasticity flows into the glassy phases. To meet this need, here we focus on gaining the physical insights into the dislocation-ACI reaction in A/C-MCs through atomistic simulations. We have (i) digitally resembled an interface structure close to that in experiments by annealing melted metallic glasses at cooling rates as low as ∼ 104 K/s; (ii) correlated the dislocation absorption events with the activation of shear transformation zones (STZs) in A/C-MCs under a plastic shear; (iii) identified the mechanisms responsible for a continuous dislocation absorption-induced instability in glassy phases; (iv) calibrated a set of constitutive relations, kinetic rules, and model parameters that can be used in an effective temperature concept-based STZ theories at the continuum level; and (v) characterized the local stress states ahead of the instability band and lay the macroscopic-level glass instability criterion on a firm atomistic basis. Our major findings are: (a) there exists a nanoscale structure transition at the ACI when the cooling rate in the atomistic simulations is reduced to an experimentally-comparable level; (b) the number of atoms participating in the STZs exponentially increases with the number of dislocations arriving at the ACI at an early stage of the dislocation-ACI reaction, but is linearly proportional to the number of absorbed dislocations at a later stage; (c) the dislocation absorption-induced instability in metallic glasses occurs through a three-stage process, i.e., the activation of STZs in the region between icosahedral (ICO) clusters, the coalescence of newly formed STZs, and then the breakdown of ICOs; (d) the model parameters in the continuum-level constitutive relations and kinetic rules are found to be sensitive to cooling rates; and (e) the local stress states ahead of the instability band in glassy phases map surprisingly well with the Mohr-Coulomb criterion regardless of the applied stress at the macroscopic level. The gained knowledge may provide a pathway of connecting the atomistic deformation physics of an A/C-MC with its overall mechanical performance, which is currently difficult to achieve in laboratory experiments. [ABSTRACT FROM AUTHOR]

This work is motivated by the goal of designing simulation software for technical devices that, at their functional core, rely on atomistic‐scale processes embedded in a larger‐scale fluid environment. The core of the problem is the conceptual and technical approach for coupling particle and continuum representations of a fluid. The state of the art for key aspects including physical modeling, mathematical formalization, computational implementation, and applications, is discussed and organized in a consistent picture across the relevant physical regimes. [ABSTRACT FROM AUTHOR]

The exchange is critical for designing high-performance Nd–Fe–B permanent magnets. Here we demonstrate through multiscale simulations that the exchange in Nd–Fe–B magnets, including bulk exchange stiffness (Ae) in Nd2Fe14B phase and interface exchange coupling strength ( J i n t ) between Nd2Fe14B and grain boundary (GB), is strongly anisotropic. Ae is larger along crystallographic a/b axis than along c axis. Even when the GB FexNd1–x has the same composition, J i n t for (100) interface is much higher than that for (001) interface. The discovered anisotropic exchange is shown to have profound influence on the coercivity. These findings enable more freedom in designing Nd–Fe–B magnets by tuning exchange. Bulk exchange stiffness in Nd2Fe14B and interface exchange coupling strength between Nd2Fe14B and grain boundary are found strongly anisotropic, which have profound influence on the coercivity of Nd–Fe–B magnets. [ABSTRACT FROM AUTHOR]

The photophysical properties of oxyluciferin, the light emitter responsible for firefly bioluminescence, are pH‐dependent. One of the potential proton acceptor/donor is adenosine monophosphate (AMP). We have studied three oxyluciferin synthetic analogues with or without AMP, in water, in the pH=5 to 11 range, using both experimental steady‐state absorption spectroscopy or the recently developed computational protocol that uses constant pH molecular dynamics and then hybrid QM/MM calculations (CpHMD‐then‐QM/MM). The latter features a systematic investigation of all the protonation microstates using molecular dynamics simulations coupled to thousands hybrid QM/MM vertical excitation energies. Our results demonstrate that AMP does not significantly modify the visible light absorption of the analogues, whatever the pH value. We also show that CpHMD‐then‐QM/MM is capable to qualitatively reproduce the pH‐dependent absorption spectrum of the analogues, despite the employed low QM level of theory. [ABSTRACT FROM AUTHOR]