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We extend the DeePMD neural network architecture to predict electronic structure properties necessary to perform non-adiabatic dynamics simulations. While learning the excited state energies and forces follows a straightforward extension of the DeePMD approach for ground-state energies and forces, how to learn the map between the non-adiabatic coupling vectors (NACV) and the local chemical environment descriptors of DeePMD is less trivial. Most implementations of machine-learning-based non-adiabatic dynamics inherently approximate the NACVs, with an underlying assumption that the energy-difference-scaled NACVs are conservative fields. We overcome this approximation, implementing the method recently introduced by Richardson [J. Chem. Phys. 158, 011102 (2023)], which learns the symmetric dyad of the energy-difference-scaled NACV. The efficiency and accuracy of our neural network architecture are demonstrated through the example of the methaniminium cation CH2 N H 2 + . [ABSTRACT FROM AUTHOR]

In past decades, enormous effort has been expended to develop algorithms and even to construct special-purpose computers in order to efficiently evaluate total energies and forces for long-range-interacting particle systems, with the particle-mesh Ewald and the fast multipole methods as well as the "Anton" series of supercomputers serving as examples for biomolecular simulations. Cutoffs in the range of the interaction have also been used for large systems. All these methods require extrapolations. Within Markov-chain Monte Carlo, in thermal equilibrium, the Boltzmann distribution can, however, be sampled natively without evaluating the total energy. Using as an example the Lennard-Jones interaction, we review past attempts in this direction and then discuss in detail the class of cell-veto algorithms that allow for the fast, native sampling of the Boltzmann distribution without any approximation, extrapolation, or cutoff even for the slowly decaying Coulomb interaction. The computing effort per move remains constant with increasing system size, as we show explicitly. We provide worked-out illustrations and pseudocode representations of the discussed algorithms. Python scripts are made available in an associated open-source software repository. [ABSTRACT FROM AUTHOR]

PyDFT-QMMM is a Python-based package for performing hybrid quantum mechanics/molecular mechanics (QM/MM) simulations at the density functional level of theory. The program is designed to treat short-range and long-range interactions through user-specified combinations of electrostatic and mechanical embedding procedures within periodic simulation domains, providing necessary interfaces to external quantum chemistry and molecular dynamics software. To enable direct embedding of long-range electrostatics in periodic systems, we have derived and implemented force terms for our previously described QM/MM/PME approach [Pederson and McDaniel, J. Chem. Phys. 156, 174105 (2022)]. Communication with external software packages Psi4 and OpenMM is facilitated through Python application programming interfaces (APIs). The core library contains basic utilities for running QM/MM molecular dynamics simulations, and plug-in entry-points are provided for users to implement custom energy/force calculation and integration routines, within an extensible architecture. The user interacts with PyDFT-QMMM primarily through its Python API, allowing for complex workflow development with Python scripting, for example, interfacing with PLUMED for free energy simulations. We provide benchmarks of forces and energy conservation for the QM/MM/PME and alternative QM/MM electrostatic embedding approaches. We further demonstrate a simple example use case for water solute in a water solvent system, for which radial distribution functions are computed from 100 ps QM/MM simulations; in this example, we highlight how the solvation structure is sensitive to different basis-set choices due to under- or over-polarization of the QM water molecule's electron density. [ABSTRACT FROM AUTHOR]

Accurate modeling of intermolecular repulsion is an integral component in force field development. Although repulsion can be explicitly calculated by applying the Pauli exclusion principle, this approach is computationally viable only for systems of limited sizes. Instead, it has previously been shown that repulsion can be reformulated in a "classical" picture: the Pauli exclusion principle prohibits electrons from occupying the same state, leading to a depletion of electronic charge between atoms, giving rise to an enhanced nuclear–nuclear electrostatic repulsion. This classical picture is called the isotropic S2/R approximation, where S is the overlap and R is the interatomic distance. This approximation accurately captures the repulsion of isotropic atoms such as noble gas dimers; however, a key deficiency is that it fails to capture the angular dependence of the repulsion of anisotropic molecules. To include directionality, the wave function must at least be a linear combination of s and p orbitals. We derive a new anisotropic S2/R repulsion model through the inclusion of the anisotropic p orbital term in the total wave function. Because repulsion is pairwise and decays rapidly, it can be truncated at a short range, making it amenable for efficient calculation of energy and forces in complex biomolecular systems. We present a parameterization of the S101 dimer database against the ab initio benchmark symmetry-adapted perturbation theory, which yields an rms error of only 0.9 kcal/mol. The importance of the anisotropic term is demonstrated through angular scans of water–water dimers and dimers involving halobenzene. Simulation of liquid water shows that the model can be computed efficiently for realistic system sizes. [ABSTRACT FROM AUTHOR]

As the most important solvent, water has been at the center of interest since the advent of computer simulations. While early molecular dynamics and Monte Carlo simulations had to make use of simple model potentials to describe the atomic interactions, accurate ab initio molecular dynamics simulations relying on the first-principles calculation of the energies and forces have opened the way to predictive simulations of aqueous systems. Still, these simulations are very demanding, which prevents the study of complex systems and their properties. Modern machine learning potentials (MLPs) have now reached a mature state, allowing us to overcome these limitations by combining the high accuracy of electronic structure calculations with the efficiency of empirical force fields. In this Perspective, we give a concise overview about the progress made in the simulation of water and aqueous systems employing MLPs, starting from early work on free molecules and clusters via bulk liquid water to electrolyte solutions and solid–liquid interfaces. [ABSTRACT FROM AUTHOR]

We present an algorithm to find first order saddle points on the potential energy surface (PES). The algorithm is formulated as a constrained optimization problem that involves two sets of atomic coordinates (images), a time-varying distance constraint and a constraint on the energy difference. Both images start in different valleys of the PES and are pulled toward each other by gradually reducing the distance. The search space is restricted to the pairs of configurations that share the same potential energy. By minimizing the energy while the distance shrinks, a minimum of the constrained search space is tracked. In simple cases, the two images are confined to their respective sides of the barrier until they finally converge near the saddle point. If one image accidentally crosses the barrier, the path is split at suitable locations and the algorithm is repeated recursively. The optimization is implemented as a combination of a quasi-Newton optimization and a linear constraint. The method was tested on a set of Lennard-Jones-38 cluster transitions and a set of 121 molecular reactions using density functional theory calculations. The efficiency in terms of energy and force evaluation is better than with competing methods as long as they do not switch to single-ended methods. The construction of a continuous search path with small steps and the ability to focus on arbitrary subsegments of the path provide an additional value in terms of robustness and flexibility. [ABSTRACT FROM AUTHOR]

Increasingly, society requires high power, high energy storage devices for applications ranging from electric vehicles to buffers on the electric grid. Supercapacitors are a promising contribution to meeting these demands, though there still remain unsolved practical problems. Molecular dynamics simulations can shed light on the relevant molecular level processes in electric double layer capacitors, but these simulations are computationally very demanding. Our focus here is on the algorithmic complexity of the constant potential method (CPM), which uses dedicated electrostatics solvers to maintain a fixed potential difference between two conducting electrodes. We show how any standard electrostatics solver—capable of calculating the energies and forces on all atoms—can be used to implement CPM with a minimum of coding. As an example, we compare our generalized implementation of CPM, based on invocations of the particle–particle–particle–mesh routine of the Large-scale Atomic/Molecular Massively Parallel Simulator, with a traditional implementation based on a dedicated re-implementation of Ewald summation. Both methods yield comparable results on four test systems, with the former achieving a substantial gain in speed and improved scalability. The step from dedicated electrostatic solvers to generic routines is made possible by noting that CPM's traditional narrow Gaussian point-spread of atomic charges on the electrodes effectively endows point-like atoms with chemical hardness, i.e., an intra-atomic energy quadratic in the charge. [ABSTRACT FROM AUTHOR]

We propose exchanging the energy functionals in ground-state density-functional theory with physically equivalent exact force expressions as a new promising route toward approximations to the exchange–correlation potential and energy. In analogy to the usual energy-based procedure, we split the force difference between the interacting and auxiliary Kohn–Sham system into a Hartree, an exchange, and a correlation force. The corresponding scalar potential is obtained by solving a Poisson equation, while an additional transverse part of the force yields a vector potential. These vector potentials obey an exact constraint between the exchange and correlation contribution and can further be related to the atomic shell structure. Numerically, the force-based local-exchange potential and the corresponding exchange energy compare well with the numerically more involved optimized effective potential method. Overall, the force-based method has several benefits when compared to the usual energy-based approach and opens a route toward numerically inexpensive nonlocal and (in the time-dependent case) nonadiabatic approximations. [ABSTRACT FROM AUTHOR]

We present a Δ-machine learning model for obtaining Kohn–Sham accuracy from orbital-free density functional theory (DFT) calculations. In particular, we employ a machine-learned force field (MLFF) scheme based on the kernel method to capture the difference between Kohn–Sham and orbital-free DFT energies/forces. We implement this model in the context of on-the-fly molecular dynamics simulations and study its accuracy, performance, and sensitivity to parameters for representative systems. We find that the formalism not only improves the accuracy of Thomas–Fermi–von Weizsäcker orbital-free energies and forces by more than two orders of magnitude but is also more accurate than MLFFs based solely on Kohn–Sham DFT while being more efficient and less sensitive to model parameters. We apply the framework to study the structure of molten Al0.88Si0.12, the results suggesting no aggregation of Si atoms, in agreement with a previous Kohn–Sham study performed at an order of magnitude smaller length and time scales. [ABSTRACT FROM AUTHOR]

Coarse-grained (CG) interactions determined via bottom-up methodologies can faithfully reproduce the structural correlations observed in fine-grained (atomistic resolution) systems, yet they can suffer from limited extensibility due to complex many-body correlations. As part of an ongoing effort to understand and improve the applicability of bottom-up CG models, we propose an alternative approach to address both accuracy and transferability. Our main idea draws from classical perturbation theory to partition the hard sphere repulsive term from effective CG interactions. We then introduce Gaussian basis functions corresponding to the system's characteristic length by linking these Gaussian sub-interactions to the local particle densities at each coordination shell. The remaining perturbative long-range interaction can be treated as a collective solvation interaction, which we show exhibits a Gaussian form derived from integral equation theories. By applying this numerical parametrization protocol to CG liquid systems, our microscopic theory elucidates the emergence of Gaussian interactions in common phenomenological CG models. To facilitate transferability for these reduced descriptions, we further infer equations of state to determine the sub-interaction parameter as a function of the system variables. The reduced models exhibit excellent transferability across the thermodynamic state points. Furthermore, we propose a new strategy to design the cross-interactions between distinct CG sites in liquid mixtures. This involves combining each Gaussian in the proper radial domain, yielding accurate CG potentials of mean force and structural correlations for multi-component systems. Overall, our findings establish a solid foundation for constructing transferable bottom-up CG models of liquids with enhanced extensibility. [ABSTRACT FROM AUTHOR]

The introduction of modern Machine Learning Potentials (MLPs) has led to a paradigm change in the development of potential energy surfaces for atomistic simulations. By providing efficient access to energies and forces, they allow us to perform large-scale simulations of extended systems, which are not directly accessible by demanding first-principles methods. In these simulations, MLPs can reach the accuracy of electronic structure calculations, provided that they have been properly trained and validated using a suitable set of reference data. Due to their highly flexible functional form, the construction of MLPs has to be done with great care. In this Tutorial, we describe the necessary key steps for training reliable MLPs, from data generation via training to final validation. The procedure, which is illustrated for the example of a high-dimensional neural network potential, is general and applicable to many types of MLPs. [ABSTRACT FROM AUTHOR]

Metamaterial design approaches, which integrate structural elements into material systems, enable the control of uncommon behaviours by decoupling local and global properties. Leveraging this conceptual framework, metamaterial adhesives incorporate nonlinear cut architectures into adhesive films to achieve unique combinations of adhesion capacity, release, and spatial tunability by controlling how cracks propagate forward and in reverse directions during separation. Here, metamaterial adhesive designs are explored with triangular cut features while integrating hierarchical and secondary cut patterns among primary nonlinear cuts. Both cut geometry and secondary cut features tune adhesive force capacity and energy of separation. Importantly, the size and spacing of cut features must be designed around a critical length scale. When secondary cut features are greater than a critical length, cracks can be steered in multiple directions, going both forward and backwards within a primary attachment element. This control over crack dynamics enhances the work of separation by a factor of 1.5, while maintaining the peel force relative to a primary cut. If hierarchical cut features are too small or too compliant, they interact and do not distinctly modify crack behaviour. This work highlights the importance of adhesive length scales and stiffness for crack control and attachment characteristics in adhesive films. This article is part of the theme issue 'Origami/Kirigami-inspired structures: from fundamentals to applications'. [ABSTRACT FROM AUTHOR]

The intensity of coastal erosion is a measure of the strength of erosion processes affecting coastal areas. Traditionally, assessments of coastal erosion intensity have relied on singular indices, such as the rate of shoreline retreat or erosion, often prioritizing higher rates over lower ones. This approach, however, lacks comprehensive consideration and scientific rigor. In this study, we adopt a more holistic approach by examining the Qionghai-Wanning coast on the eastern side of Hainan Island. We selected four indices that reflect local conditions and influence coastal erosion strength: Annual rate of shoreline change (T1), Beach annual down-cutting rate (T2), Beach slope (T3), Average particle size of the beach (T4). These indices were used to comprehensively evaluate the erosion intensity of the Qionghai-Wanning coast. The evaluation results categorized the study area into six grades: serious erosion (3.45%), strong erosion (6.90%), erosion (20.69%), micro erosion (44.38%), stabilization (20.69%), and accretion (3.45%). The findings indicate that, under the broader environmental trends of global warming and rising sea levels, most sandy coasts exhibit micro-erosion intensity. Areas experiencing strong and serious erosion are predominantly influenced by human activities, such as those occurring in promenade bays, artificial islands, and harbors. To further understand the relationship between these factors and erosion intensity, we employed the Spearman correlation coefficient method. The analysis revealed that the T1 and the T2 are the primary factors influencing coastal erosion intensity, with the T4 serving as a secondary factor. These factors collectively impact the force and energy absorption of the coast through wave and tidal actions, ultimately determining the intensity of coastal erosion. The multi-index assessment method for coastal erosion intensity demonstrated an accuracy of 82.75%, providing a scientific basis for the management, protection, and restoration of coastal areas. [ABSTRACT FROM AUTHOR]

In this study, the oxidation of Ga–polar GaN(0001) surface simulated by using originally developed charge‐transfer‐type interatomic potential is reported on. The adjusted potential parameters reproduce the cohesive energies in the range of 0.3 eV atom−1 and atomic forces with correlation coefficient as high as 0.9, compared to the results of first‐principles calculations for more than 9000 structures associated with oxidation of GaN. The oxidation simulations reveal the formation of a periodic gallium oxide (GaOx) layer grown on GaN(0001) with O atoms replacing N atoms. The atomic distance between Ga–Ga in the GaOx layer along GaN[0001] direction is 3.05 Å, which is longer than wurtzite GaN (2.63 Å) and is quantitatively in agreement with the recent photoelectron holography measurement. The distances of the Ga atoms projected onto the GaN(11–20) plane are determined to be 3.19 Å for the GaOx layer and 2.79 Å for the interfacial GaN. These distances also align quantitatively with the scanning transmission electron microscopy imaging of the native oxide on GaN(0001). Further oxidation simulation in a larger model of 2304 atoms suggests the formation of the layered structure even in the subsequent layers away from the interface of GaN and gallium oxide. [ABSTRACT FROM AUTHOR]

As a typical passive energy dissipation device, the fluid viscous damper (FVD) is widely utilized for structural vibration control. However, performance degradation in FVDs has been highlighted, particularly concerning the gap effect resulting from the imperfect installation and insufficient fluid. This study proposes three analytical models to characterize the gap property in the hysteresis behavior of FVDs, including the Gap model (G. model), the Equivalence model (E. model), and the Stiffness Degradation model (S. model). The purpose of the G. model is to reproduce the zero-force platform in the hysteresis curve. The E. model and S. model are both simplified models, aiming to consider the gap effect by altering the damping coefficient, velocity exponent, and stiffness based on the energy and maximum force equivalence principles. Shake table tests of a single-degree-of-freedom system are carried out to validate and assess the effectiveness and accuracy of these three methods. The results indicate that the gap effect will significantly degrade the vibration mitigation performance of FVDs, and hence it needs to be considered in simulations. The displacement and force obtained using the G. model under distinct loads highly correspond to the experimental results. By adopting the simplified models, satisfactory results can be derived with a lower implementation cost. Among them, the E. model is more appropriate when subjected to harmonic loads, while the S. model is suggested for cases under seismic excitations. [ABSTRACT FROM AUTHOR]

Cellulose nanocrystals (CNCs), derived from abundant natural cellulose, possess exceptional properties including low weight, bioavailability, and high mechanical performance. During shear loading, CNCs exhibit unique stick–slip behavior, making them excellent toughening materials for CNC neat films and nanocomposite. However, the failure behavior at the interface under specific conditions, particularly moisture and temperature, remains unclear. The study utilized molecular dynamics (MD) simulations to quantitatively investigate the hydrothermal effect on the degradation of CNC interface. The degradation mechanism induced by moisture and temperature was indicated through the reduction of adhesive energy and peak force with the consideration of hydrogen bonds. The simulation results showed that the role of water molecules in the interfacial failure depends their content. Water acted as a binder at low moisture levels, while at high moisture levels, it acted as a lubricant. Besides, temperature had a more pronounced impact on the interfacial shear performance. Our simulation results can be used as input in micromechanical models to bridge the gap between the macroscopic and microscopic behavior of films and nanocomposites. [ABSTRACT FROM AUTHOR]

Background: The recent development of Physics-Augmented Neural Networks (PANN) opens new opportunities for modeling material behaviors. These approaches have demonstrated their efficiency when trained on synthetic cases. Objective: This study aims to demonstrate the effectiveness of training PANN using real experimental data for modeling hyperelastic behavior. Methods: The approach involved two uni-axial experiments equipped with digital image correlation and force sensors. The tests achieved axial deformations exceeding 200% and presented non-linear responses. Twenty loading steps extracted from one experiment were used to train the PANN. The model architecture was optimized based on results from a validation dataset, utilizing equilibrium gap loss computed on six loading steps. Finally, 544 loading steps from the first experiment and 80 steps from a second independent experiment were used for testing purposes. Results: The PANN model effectively captured the hyperelastic behavior across and beyond the training loads, showing superior performance compared to the standard Neo-Hookean model when assessed using various evaluation metrics. Conclusions: Training PANN with experimental mechanical data shows promising results, outperforming traditional modeling approaches. [ABSTRACT FROM AUTHOR]

This paper aims to examine the behavior of cracked adhesive joints experimentally and numerically when they are subjected to quasi-static and dynamic loads using the tensile and falling-wedge impact tests, respectively. Double cantilever beam (DCB) specimens were manufactured and tested under impact loading with varying impact energies to analyze the adhesive joint mode-I dynamic fracture response. To determine quasi-static and dynamic mode-I fracture energies, the compliance-based beam method (CBBM) was utilized accounting for the axial force exerted by the wedge. It was found that by changing the loading condition from quasi-static to impact, the maximum force and fracture energy of adhesively bonded joints were considerably increased by 275% and 452%, respectively. However, within the impact test conditions, increases of 10% and 22% were obtained in maximum force and fracture energy when the impact energy was tripled. The adhesive joints tested under static loading experienced a mixed interfacial/cohesive failure pattern, whereas by shifting the loading condition to impact, the failure pattern turned fully cohesive. The quasi-static and dynamic fracture responses of adhesive joints were modeled using the cohesive zone model employing a triangular traction-separation law. The numerical and experimental results exhibited reasonable correlation. [ABSTRACT FROM AUTHOR]

• Cells increase traction forces and energy usage with substrate stiffness. • Cells on stiffer substrates convert energy into traction forces more efficiently. • Cell behaviors are regulated by both energy production and utilization efficiency. To form blood vessels, endothelial cells rearrange their cytoskeleton, generate traction stresses, migrate, and proliferate, all of which require energy. Despite these energetic costs, stiffening of the extracellular matrix promotes tumor angiogenesis and increases cell contractility. However, the interplay between extracellular matrix, cell contractility, and cellular energetics remains mechanistically unclear. Here, we utilized polyacrylamide substrates with various stiffnesses, a real-time biosensor of ATP, and traction force microscopy to show that endothelial cells exhibit increasing traction forces and energy usage trend as substrate stiffness increases. Inhibition of cytoskeleton reorganization via ROCK inhibition resulted in decreased cellular energy efficiency, and an opposite trend was found when cells were treated with manganese to promote integrin affinity. Altogether, our data reveal a link between matrix stiffness, cell contractility, and cell energetics, suggesting that endothelial cells on stiffer substrates can better convert intracellular energy into cellular traction forces. Given the critical role of cellular metabolism in cell function, our study also suggests that not only energy production but also the efficiency of its use plays a vital role in regulating cell behaviors and may help explain how increased matrix stiffness promotes angiogenesis. [ABSTRACT FROM AUTHOR]

The interaction between an atom and the quantized electromagnetic field depends on the position of the atom, leading to a force which is the negative gradient of this interaction. At zero temperature, the mean of this force vanishes, but it has a nonzero value for a thermal electromagnetic background. By applying the Heisenberg equations of motion and the Born–Markov approximation, we obtain the mean and correlation of the force, which show that the center-of-mass motion of the atom is damped and diffused. This approach can be easily extended to multi-level atoms, and it is shown that the damping force and diffusion coefficients are invariant under Galilean transformations. In principle, this effect can be utilized to determine the velocity of the laboratory relative to the thermal background. [ABSTRACT FROM AUTHOR]

AbstractChiral honeycomb structures, renowned for their superior mechanical properties, find extensive application in passive safety protection and beyond. However, existing research predominantly centers on chiral honeycomb structures, neglecting discussions on the energy absorption capabilities of anti-chiral honeycomb structures subjected to out-of-plane impacts. In view of this, an innovative design method is proposed in this paper to construct a series of anti-tri-chiral honeycomb structures (MATCH-θ) with missing rib-plate and excellent crashworthiness by skillfully designing and replacing the nodal elements of the anti-tri-chiral structures. Subsequently, the effects of the constitutive angle θ and the wall thickness t of the cellular elements were investigated using a validated finite element model, revealing the energy absorption mechanism of MATCH-θ. It is shown that this type of structure has better crashworthiness performance compared to the conventional anti-tri-chiral honeycomb structure ATCH-90°. In particular, the MATCH-110° structure with t = 0.1 mm showed a 36% increase in specific energy absorption, a 36% increase in mean crush force, and a 35% increase in crush force efficiency compared to the conventional anti-tri-chiral honeycomb structure ATCH-90° with the same mass. The completion of this study provides valuable insights into the design and optimization of future honeycomb structures for crashworthiness. [ABSTRACT FROM AUTHOR]

Traditional mesh‐based methods for cutting deformable bodies rely on modifying the simulation mesh by deleting, duplicating, deforming or subdividing its elements. Unfortunately, such topological changes eventually lead to instability, reduced accuracy, or computational efficiency challenges. Hence, state of the art algorithms favor the extended finite element method (XFEM), which decouples the cut geometry from the simulation mesh, allowing for stable and accurate cuts at an additional computational cost that is local to the cut region. However, in the 3‐dimensional setting, current XFEM frameworks are limited by the cutting configurations that they support. In particular, intersecting cuts are either prohibited or require sophisticated special treatment. Our work presents a general XFEM formulation that is applicable to the 1‐, 2‐, and 3‐dimensional setting without sacrificing the desirable properties of the method. In particular, we propose a generalized enrichment which supports multiple intersecting cuts of various degrees of non‐linearity by leveraging recent advances in robust mesh‐Boolean technology. This novel strategy additionally enables analytic discontinuous integration schemes required to compute mass, force and elastic energy. We highlight the simplicity, expressivity and accuracy of our XFEM implementation across various scenarios in which intersecting cutting patterns are featured. [ABSTRACT FROM AUTHOR]

Wave energy holds significant promise as a renewable energy source due to the consistent and predictable nature of ocean waves. However, optimizing wave energy devices is essential for achieving competitive viability in the energy market. This paper presents the application of a nonlinear model predictive controller (MPC) to enhance the energy extraction of a heaving point absorber. The wave energy converter (WEC) model accounts for the nonlinear dynamics and static Froude–Krylov forces, which are essential in accurately representing the system's behavior. The nonlinear MPC is tested under irregular wave conditions within the power production region, where constraints on displacement and the power take-off (PTO) force are enforced to ensure the WEC's safety while maximizing energy absorption. A comparison is made with a linear MPC, which uses a linear approximation of the Froude–Krylov forces. The study comprehensively compares power performance and computational costs between the linear and nonlinear MPC approaches. Both MPC variants determine the optimal PTO force to maximize energy absorption, utilizing (1) a linear WEC model (LMPC) for state predictions and (2) a nonlinear model (NLMPC) incorporating exact Froude–Krylov forces. Additionally, the study analyzes four controller configurations, varying the MPC prediction horizon and re-optimization time. The results indicate that, in general, the NLMPC achieves higher energy absorption than the LMPC. The nonlinear model also better adheres to system constraints, with the linear model showing some displacement violations. This paper further discusses the computational load and power generation implications of adjusting the prediction horizon and re-optimization time parameters in the NLMPC. [ABSTRACT FROM AUTHOR]

Thin-walled metal structures are known as an effective solution in absorbing impact energy and reducing the resulting reaction forces. The design of energy absorbers with higher energy absorption capability, lower weight and reaction forces, as well as lower manufacturing cost, has always been of interest. In this study, the effects of diameter and thickness of thin-walled Aluminum tubes on different crashworthiness criteria were investigated. To this end, different geometries were examined by simulating the uniaxial compressive test applying the finite element method. The results revealed that the optimal diameter for a simple circular tube (SCT), assuming constant length and thickness, is the smallest diameter in terms of resistance to global buckling. The SCT with an optimal diameter has the highest specific energy absorption (SEA), the lowest maximum crushing force ( F max ), and the highest crushing force efficiency (CFE). Moreover, in this study, the effect of thickness on the tubular absorber performance was numerically investigated according to four criteria: SEA, F max , CFE, and energy absorption (EA), and the optimal dimensions were obtained. Based on the results, increasing the thickness increases CFE, and increasing the ratio of thickness to diameter (t/D) increases SEA and CFE. Eventually, by applying the regression analysis, two equations were presented to calculate F max and CFE, which can be used to predict the performance of thin-walled metal tubes. Reducing the tube diameter reduces the force fluctuations during crushing. SEA increases by increasing the tube thickness specially for small diameters. As thickness-to-diameter ratio (t/D) increases, SEA and CFE increase. Three different objective functions were carried out to find the optimum tube. Obtained fitted equations predict the maximum crushing force and force efficiency. [ABSTRACT FROM AUTHOR]

Distraction Osteogenesis (DO) revolutionizes bone lengthening without donor sites, which is crucial in maxillofacial reconstruction (MRA). Manual DO devices are standard, but continuous DO devices promise faster treatments and better outcomes. Current continuous distractors lack ideal MRA due to size, force generation, and power source limitations. This study introduces a passive distractor system for continuous DO in MRA, aiming to bridge existing gaps and provide an ideal solution for human MRA use. It utilizes a miniaturized mechanism powered by a passive energy source, eliminating the need for active power. Advanced manufacturing methods enable the reduction of device size while hydraulic systems ensure controlled and smooth movement. The system includes a proximal bone fixture, movable distractor components, and passive drive means for distraction force application. Results show promising potential to address existing limitations. By utilizing passive energy for continuous force generation, the device size is reduced, and the need for force transition mechanisms is minimized. This innovative system and method offer an ideal treatment environment for MRA in humans. Further research and clinical evaluation are essential to validate its efficacy and safety in clinical practice. [ABSTRACT FROM AUTHOR]

It was recently shown that integrating out M2 states on Calabi‐Yau manifolds captures non‐perturbative topological string physics in the free energy. In this note, It has been shown that the resulting expression manifests a certain duality symmetry: the free energy at strong string coupling is equal to the Calabi‐Yau period at weak string coupling. The duality yields the appropriate prescription for completing the integrating out in the ultraviolet. [ABSTRACT FROM AUTHOR]

Introduction: Leprosy is a chronic, slowly developing infectious disease that affects the peripheral nerves, specifically Schwann cells. Individuals with the multibacillary type exhibit a propensity for developing chronic pain and a decrease in sensitivity in the plantar region, which directly interferes with balance maintenance. The evaluation of static balance in this population is made through the measurement of the center of pressure (COP) oscillations. Therefore, there is a need to investigate the association between postural control and COP oscillations using a force platform and finding accelerations of the center of mass (COM) from inertial sensors for reliable and portable balance assessment in leprosy patients. Objective: To validate the application of inertial sensors for patients with leprosy by establishing a correlation with the outcomes obtained from a force platform. Methods: This is an observational study with a case-control design, in which 30 participants with leprosy and 30 healthy participants were recruited to evaluate static balance using an inertial sensor and a force platform. Participants underwent balance assessment under two conditions (Eyes Open: OE and Eyes Closed: CE), and data from the platform and sensor were processed using Matlab computational routines. The data were quantified using four parameters: Total Displacement (TD), Area, Antero-Posterior Displacement (APdisp), and Medio-Lateral Displacement (MLdisp). Results: The evaluated parameters showed significantly different values between the groups, where the Leprosy group exhibited significantly higher values compared to the control group, both in the OE and CE conditions for all four parameters. The sensor corroborated the differences demonstrated by the platform and followed the same trend for medio-lateral displacements and accelerations. It can be observed that the evaluated parameters exhibited a varied correlation ranging from moderate to large between the platform and the sensor. Among the four variables, MLdisp had the lowest correlation. Discussion: The results partially confirmed the first hypothesis of concurrent validation, showing a moderate to large correlation between the force platform and the inertial sensor. The second hypothesis of clinical validation was also partially confirmed, as not all group differences observed in the COP measurements from the force platform were reflected in the COM measurements from the inertial sensor. Specifically, the force platform indicated greater oscillations in participants with multibacillary leprosy compared to controls, a finding statistically confirmed by the sensor for all measures except MLdisp. Conclusion: This research confirmed the concurrent validity of the inertial sensor with the force platform and its clinical validation, demonstrating that this instrument can be applied in clinical settings due to its low cost and ease of use. The findings may contribute to public health by identifying postural control tools for patients with multibacillary leprosy. Author summary: Our study aimed to validate the application of inertial sensors for patients with leprosy by establishing a correlation with the outcomes obtained from a force platform. Due to the disease's impact on sensory perception and chronic pain in the plantar region, maintaining balance becomes challenging for affected individuals. Using a force platform and an inertial sensor, we evaluated balance in 30 leprosy patients and 30 healthy participants under Eyes Open and Eyes Closed conditions. Results revealed significantly higher values in balance parameters for the leprosy group compared to controls, indicating greater instability. The inertial sensor confirmed these differences, particularly in medio-lateral displacements and accelerations. While correlation between the platform and sensor varied, our study validated the sensor's concurrent and clinical efficacy. This research underscores the potential of inertial sensors as reliable, cost-effective tools for assessing balance in clinical settings, especially for patients with multibacillary leprosy. Our findings contribute to enhancing public health efforts by offering practical solutions for monitoring and managing balance deficits in this neglected disease population. [ABSTRACT FROM AUTHOR]

Previous studies of two-dimensional (2D) aerodynamic admittance function (AAF) identification methods have basically ignored the effects of different turbulence components, which may lead to unpredictable errors for practical engineering applications. This paper presents pressure measurement experiments on thin sections with a geometric ratio of 1:50 in various turbulent fields. Based on the three-dimensional (3D) two-wavenumber theoretical analytical framework, the two-wavenumber coherence function is obtained by fitting the measured spanwise root-coherence function at the effective spacing with an empirical model. A new method is proposed, assuming that the ratio relationship between the lift AAFs due to longitudinal and vertical turbulence components of the measured model section satisfies its corresponding theoretical solution ratio relationship. The 2D lift AAFs of the airfoil section induced by different turbulence components are identified following the proposed identification framework. Consistent with the previous research, force correlation is significantly larger than turbulence correlation, and the traditional 3D one-wavenumber AAFs obtained are different in different turbulent fields. The separated 2D lift AAFs demonstrate that the contributions of u- and w- turbulence to the buffeting lift force are significantly different, and are more precise, according to the ratio between the Horlock function and Sears function. Then, the method is successfully extended to estimate the AAFs with respect to the u- and w-turbulence components of a streamlined box girder section, further validating the applicability of the identification method to the streamlined box girder. Furthermore, comparing the separated 2D lift AAFs under different turbulence fields reveals their independence from turbulence characteristics. [ABSTRACT FROM AUTHOR]

To solve the problem of the lack of physical properties of pedicels and the changing pattern for designing the end-effector of tomato harvesting robot and different harvesting modes, research was conducted on the physical properties of tomato pedicels and their change patterns. Using a Universal TA texture analyzer, tensile, three-point bending, and shearing tests were performed on tomato pedicels in the early firm-ripening stage. The tomato variety used was Syngenta Spectrum, cultivated seasonally with two crops per year. Spring crop tomatoes were used in this study. The experimental results provide a theoretical basis for designing tomato harvesting robots across three harvesting modes. Tensile tests measured the pull-off force and tensile strength of the abscission zone with varying diameters. These results are crucial for designing robots using a tensile harvesting mode. The location of the tomato pedicel significantly affects the shearing force. A one-way test was conducted on the shearing part. The results showed that the shearing force and energy required for the proximal pedicel are significantly greater than for the distal pedicel. To reduce the shearing force and energy needed by the end-effector's shearing mechanism on distal pedicels, a response surface test was conducted. Three factors were examined: shearing speed, angle, and distal pedicel diameter. Design–Expert software optimized these factors to minimize shearing energy and force, leading to the best shearing parameters for different distal pedicel diameters. From the three-point bending tests, the average maximum bending breaking force, bending modulus, and bending strength of the tomato abscission zone were determined. These findings offer a theoretical basis for designing tomato harvesting robots with a bending-type harvesting mode. [ABSTRACT FROM AUTHOR]

Much attention has been focused on viscoelastic microfluidics which can be widely used for the focusing and separation of particles/cells in continuous flows without any external force or energy. In this study, we demonstrate that microparticles can be separated by the elasto-inertial focusing and the concentration gradient of viscoelastic fluid in a microchannel with a rhombic cross-sectional shape. We have already presented a simple and robust fabrication method for microchannel with the rhombic cross-section, which was used for particle focusing in viscoelastic polyethylene oxide (PEO) solution. Using the fabricated microfluidic device, we observed the behavior of particles by size in viscoelastic fluids with various concentration gradients and presented their focusing and separation. Separation experiments were performed on 12, 5.0, and 2.1 µm particles, and the optimal separation conditions were sought according to flow rate, sample-to-sheath flow rate ratio, and PEO concentration gradient. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) warp interlock woven composites (3DWIWC) are in demand in various industries due to their excellent delamination resistance, damage tolerance and fracture toughness properties. The 3D warp interlock woven fabric architecture can be defined by numerous fabric parameters such as: the binding and stuffer warp yarns, the woven pattern, the presence of yarn groups, etc. .... The effect of the fabric architecture on the impact behaviour of 3DWIWC made with carbon yarns has not been fully investigated. The binding warp yarns with the weave pattern play the main role in the arrangement of yarns within the final composite. In order to highlight their main influence, the 3D woven composites had been differentiated according to the main fabric architectural parameters, which are the angle and depth of binding warp yarn, presence of stuffer warp yarn and weave pattern of binding warp yarn. Afterward, their low velocity impact properties and damage mechanisms were examined. Thanks to the precise combination of these internal parameters of the fabric architecture, the contact force and absorbed energy values of 3DWIWC could be increased almost %50 and %15, respectively. Moreover, their damage mechanisms could be significantly improved. [ABSTRACT FROM AUTHOR]

High voltage electric pulse (HVEP) was used to perform concrete cracking experiments to demonstrate the feasibility of this technique for cracking hard objects. The results of the study show that HVEP fracturing technology has great potential for application. This article uses a high-speed camera to record the crack expansion process, and analyze the relationship between crack expansion speed and time. The Hilbert–Huang Transform (HHT) is used to analyze the vibration signal generated by the shock waves (SWs). The energy evolution law of SWs is elaborated by the time–frequency characteristics of the vibration. The distribution of the vibration energy is more concentrated between 0 and 100 Hz. The increase of capacitance value will produce stronger vibration peak energy and force. The presence of cracks will cause the vibration energy propagation to be blocked and the energy decay rate to be accelerated. Also, the energy will be shifted in the frequency domain due to the presence of cracks. Highlights: A high-power high voltage electric pulse fracturing equipment is designed and manufactured. The process of crack formation and expansion is recorded. Hilbert–Huang transform analysis of the time–frequency characteristics of vibration signals. Increase of capacitance enhances instantaneous energy and maximum force of discharge. Cracks cause the energy decay of shock waves to become faster. [ABSTRACT FROM AUTHOR]

This paper presents spectral element based approach for determining free planner wave propagation in two-dimensional periodic square-frame-grid-lattices (SqL). Implementing the newly developed nonlinear eigenvalue solver in conjunction with Bloch–Floquet periodic boundary condition, band structures for various configurations of SqL with attached mass or spring-mass resonator are analysed. Variation of the attenuation bandwidth is studied for different mass and frequencies of the attachments to the SqL. At the natural frequency of the resonator, an attenuation bandgap can be perceived; therefore, by tuning the natural frequency of the resonator, sub-wavelength band-gap can be obtained at the desired frequency for enhanced vibration or noise isolation. However, in few cases, mostly while the resonators are attached at the center point of the SqL, the attenuation bandgap near the natural frequency of the resonator may disappear as the center point lying in the node for that free wave frequency. Additionally, existence of dirac cone, eigenfrequency-loci veering are observed in the band-structures. The iso-frequency contours are also investigated to develop an insight comprehension about the underlying physics of energy transmission and mechanics of wave propagation. Various salient wave propagation features, namely self-collimation, lensing, and negative refraction of group velocity are identified and elucidated in this paper. [ABSTRACT FROM AUTHOR]

A rhombus-nested compliant amplification mechanism is proposed for versatile usages of precision actuators and force sensors with an easy tuning of stiffness. Such a monolithically planar rhombus-nested compliant mechanism has the dual functions of two-stage displacement or force amplification by changing the input and output ports. It features a large ratio of inter-stage stiffness, thus resulting in an enhanced amplification ratio, load capacity and dynamic bandwidth. The geometrically nonlinear analytical equations of displacement amplification ratio and input stiffness are derived in the presence of pronounced axially-loaded stiffening and kinematic-arching effects based on the beam constraint model. It allows an insightful evaluation of geometrically nonlinear deformation behaviors sensitive to structural dimensions in a parametric way. Insights into geometrically nonlinear behaviors in the case of large-stroke and axially-loaded motions are discussed as well. A proof-of-concept prototype with embedded piezoelectric stacks is fabricated with the dimensions of 74mm × 60mm × 10 mm. The dual functions of precision actuator with amplified motion strokes and force sensor with enhanced sensitivity are experimentally demonstrated. [Display omitted] • A monolithically rhombus-nested compliant amplification mechanism is designed. • Geometrically nonlinear analytical model of amplification ratio is derived. • The dual functions of a precision actuator and force sensor are demonstrated. [ABSTRACT FROM AUTHOR]

• An impact-damping model with multi-point contact and external load is proposed. • The effect of multi-point contact and external load on system impact is studied. • This impact-damping model is applied to the dynamics model of a spur gear pair. • The connection between gear system resonance and teeth impact is revealed. The damping term is an important component of the calculation model of the contact force of collision bodies because it simulates the energy dissipation of collision bodies during the contact-impact process. Therefore, an impact-damping model of a collision body with multi-point contact and external load is established by considering the restitution coefficient. The algorithm for solving this model is proposed based on iterative methods. Then, the accuracy of the established model is verified by the consistency between the calculated and tested results. The effect of multi-point contact and external load on the contact-impact process of the collision body is studied. The results show that the hysteresis damping factor increases from small to large when the collision body enters a stable state through repeated impacts. Further, the established damping model is applied to the dynamics model of a spur gear pair with backlash, extended teeth contact, and structure coupling effect of the gear body. The nonlinear dynamic characteristics, multi-state mesh, and teeth impact of the system are studied through the root-mean-square of transmission error, bifurcation diagrams with multi-mapping sections, and contact forces. The calculation results of the gear dynamics model with the impact-damping model are more consistent with the tested results than the calculation results of the gear dynamics model with the traditional damping model. Meanwhile, the connection between system resonance, response coexistence, teeth disengagement, and teeth impact is revealed. [ABSTRACT FROM AUTHOR]

Gravelly soil strata exhibit heterogeneity and nonlinearity in their physical and mechanical properties, leading to volatile fluctuations of shield scraper force. Understanding the performance of shield scrapers in gravelly soils is significant for the safe and efficient excavation of tunnel boring machines. This paper conducts unconsolidated-undrained triaxial tests to obtain the mechanical properties of gravelly soils with gravel content ranging from 0 % to 30 %. The process of shield scrapers cutting through gravelly soils is analyzed by combining the varying mechanical properties of gravelly soils with the limit equilibrium analysis method. Subsequently, modified models for predicting the scraper force and specific energy in gravelly soils are established. Based on these models, the impact of key factors on the scraper performance is analyzed. Laboratory experiments are further performed on a rotary test bench to validate these models. The experimental results demonstrate that the horizontal cutting force and specific energy of shield scrapers in gravelly soils can be predicted with mean average errors of 8.8 % and 7.3 %, respectively, with the errors of all predicted values falling within ±20 % of the experimental results. These established models can serve as useful references for the structural and operational design of shield scrapers in gravelly soil strata. [ABSTRACT FROM AUTHOR]

The influence of key design parameters on the constant force characteristics of long-stroke moving-iron proportional solenoid actuators (MPSAs) has been explored by a method combining finite element modelling and correlation analysis. First, the finite element model (FEM) of long-stroke MPSA was developed and validated. Subsequently, the two evaluation indexes, the average-output solenoid force and maximum-output solenoid force variability, were introduced to disclose the influence law of pole shoe parameters on the constant force characteristics of a long-stroke MPSA. After that, correlation analysis was employed to quantify the influence of several parameters and parameter interaction factors on the constant force characteristics. The results indicate a strong contradiction between the average-output solenoid force and maximum-output solenoid force variability; however, increasing the inner diameter of the cone helps enhance the average-output solenoid force without causing maximum-output solenoid force variability to increase. Among all the parameters examined, the cone angle is the most significant parameter affecting the constant force characteristics. Additionally, interactions between the cone angle and the cone length, the cone angle and the inner cone diameter, the cone angle and the outer cone diameter, the cone length and the outer cone diameter, as well as the inner cone diameter and the outer cone diameter also have an important influence on the constant force characteristics. This study deepens our understanding of how the key parameters affect the constant force characteristics and assists designers in optimizing these parameters for developing new structures. [ABSTRACT FROM AUTHOR]

Middle borosilicate glass tubes are critical materials for medical packaging, with the drawing machine playing a pivotal role in their production process. However, the effects of the drawing wheel's motion parameters on the glass tube remain underexplored. Therefore, based on the finite element method simulation and validation experiment, the effects of experimental factors (angle of upper and lower drawing wheel, AUD; friction factor of glass and rubber, FFGR; and distance of upper and lower drawing wheel, DUD) on experimental indexes (maximum effective stress of glass tube, MES; rotational speed of glass tube, RSG; maximum and average forward driving force, MFDF and AFDF; maximum and average rotational driving force, MRDF and ARDF; total energy consumption and power, TEC and TPD; maximum and average forward driving power, MFDP and AFDP; and maximum and average rotational driving power, MRDP and ARDP) were analyzed. The results indicated that compared to FFGR and AUD, the influence of DUD on experimental indexes was the highest. The positive influence of AUD on RSG, ARDP, and MRDP, the positive influence of FFGR and the negative influence of DUD on MRDF, ARDF, TEC, TPD, ARDP, and MRDP were found, respectively. These findings will provide a theoretical reference for the optimization of drawing machines. [ABSTRACT FROM AUTHOR]

Ultra-low friction is crucial for the anti-friction, anti-wear, and long-life operation of nanodevices. However, very few two-dimensional materials can achieve ultra-low friction, and they have some limitations in their applications. Therefore, exploring novel materials with ultra-low friction properties is greatly significant. The emergence of ternary two-dimensional materials has opened new opportunities for nanoscale ultra-low friction. This study introduced nickel phosphorous trisulfide (NiPS3, referred to as NPS), a novel two-dimensional ternary material capable of achieving ultralow friction in a vacuum, into the large nanotribology family. Large-size and high-quality NPS crystals with up to 14 mm × 6 mm × 0.3 mm dimensions were grown using the chemical vapor transport method. The NPS nanosheets were obtained using mechanical exfoliation. The dependence of the NPS nanotribology on layer, velocity, and angle was systematically investigated using lateral force microscopy. Interestingly, the coefficient of friction (COF) of NPS with multilayers was decreased to about 0.0045 under 0.005 Pa vacuum condition (with load up to 767.8 nN), achieving the ultra-low friction state. The analysis of the frictional dissipation energy and adhesive forces showed that NPS with multilayers had minimum frictional dissipation energy and adhesive forces since the interlayer interactions were weak and the meniscus force was excluded under vacuum conditions. This study on the nanoscale friction of a ternary two-dimensional material lays a foundation for exploring the nanoscale friction and friction origin of other two-dimensional materials in the future. [ABSTRACT FROM AUTHOR]

Shipping impact and wave loads impose dynamic loads on jetties and platforms in the sea, which cause the vibration of structures. Recently, many advanced viscous damper devices have been developed for implementation in structures to diminish structural vibration due to earthquakes or wind. However, the longitudinal configuration of conventional viscous damper devices requires adequate space to locate the damper device within the frame structure, which limits the application of viscous dampers for use in jetties or platforms to dissipate the vibrations imposed by ship impact or wave force. For this reason, in this study, an attempt has been made to develop a new viscous plane damper device applicable in limited space positions where the longitudinal damper device is not able to fit. For this purpose, the initial design for the viscous plane damper device is proposed, and the prototype of the device is manufactured. Then, the performance of the fabricated viscous plane damper is examined through experimental tests by applying cyclic loads using a dynamic actuator. In order to investigate the effect of the diameter and configuration of the piston's orifices, five different diameters for the orifices of 1, 2, 5, 8, and 10 mm are included, and three different distribution configurations of the orifices in the piston plate as Configurations A, B, and C are manufactured and tested experimentally. The lab testing is conducted by applying cyclic loads with different frequencies to evaluate the performance of the developed plane damper device under various load velocities. Accordingly, the dynamic performance of the damper device, including the damping force, effective damping and stiffness and the energy dissipation capacity obtained from the hysteresis response (force–displacement result), is investigated. The results of the experimental tests prove the functionality of the developed device to generate the desired damping force and vibration energy dissipation during applied cyclic loads. Therefore, the new plane damper device can be implemented in any structure to dissipate the effect of imposed vibration. [ABSTRACT FROM AUTHOR]

The speed of sound depends on the structure and material properties of the crystal, such as density and Young's modulus. On the other hand, from atomistic arguments it is possible to associate Young's modulus with other material properties. These observations lead to a relationship between binding energy of atoms in a crystal (which is one of the parameters appearing in Mie-Lennard-Jones potential), speed of sound in the longitudinal direction and mass of one atom in the lattice. This subject was addressed by several authors, providing different implementations of this relation. A literature review on this topic is made and the mathematical derivation of the relation is carried out. Applications of this relationship to rare gases, some metals and some rare earths are presented and the results compared to others taken from literature. [ABSTRACT FROM AUTHOR]

Oblique wave scattering by a pair of partially immersed porous barriers, placed (i) on one side of (Position I), (ii) just above (Position II) and (iii) on the two sides (Position III) of a thick rectangular bottom-standing rigid obstacle, is studied here. The mathematical formulation and solution procedure of the corresponding boundary value problem are discussed using Havelock's expansion and Galerkin's approximation technique. During the solution procedure, a set of first-kind Fredholm-type integral equations is solved approximately by choosing suitable basis functions (Chebyshev and Gegenbauer polynomials). To address the singularities of order half and one-third that appear at the submerged edges of the thin barriers and the corners of the thick obstacle, appropriate basis polynomials with suitable weight functions are chosen in Galerkin's approximation. The reflection and transmission coefficients, dissipating wave energy, and dimensionless wave force are computed for various values of different parameters and depicted graphically in quite a number of figures. The numerical results for some special cases are compared with those available in the literature and excellent agreement has seen to have been achieved thus validating the correctness of the numerical method presented here. Based on numerical results it is observed that Position III of the barriers is more effective than Position I and Position II in resisting wave loads on marine areas and attenuating wave energy. [ABSTRACT FROM AUTHOR]

Banana crowns' intricate vascular systems facilitate nutrient transport for fruit growth and provide mechanical support. Analyzing vascular bundle morphology facilitates understanding of its influence on the banana de-handing process. In this study, we employed X-ray Computed Tomography (CT) scanning and microscopic observation of paraffin sections to characterize the morphological traits of the banana crown's vascular tissue system and reconstructed its 3D vascular tissue system throughout the banana bunch. Based on the internal tissue characteristics and external morphology, the banana crown is categorized into three regions: the central stalk–crown transition region (CSCTR), the crown expansion region (CER), and the crown–finger transition region (CFTR). Cutting experiments indicated that variations in the cutting strength and specific cutting energy across positions within the banana bunch were insignificant but significantly distinct among the three regions. Specifically, the CER showed a 19.7% reduction in cutting strength and a 15.5% decrease in energy consumption compared to the other regions. This was due to the unique cross-distribution of fibers within the CER, which were primarily parallel to the cutting blade, significantly reducing cutting forces and energy consumption, making the CER the optimal region for cutting. The orientation of vascular bundles relative to the blade is key to optimizing plant cutting mechanics. [ABSTRACT FROM AUTHOR]

This paper presents two methods for deformation energy or dynamic for measuring and calculating the torsion modulus, G, for composites with hollow glass microsphere (HGM) additives in unsaturated polyester resin. First, we constructed a measurement system with a torsion pendulum, a force sensor (FS), and a rotational movement sensor (RMS). Then, we deduced a relationship between force (F) and torsion angle (θ) to obtain G by deformation energy. Second, using the relaxation curve, θ in function time (t), we deduce an equation that could return the value of G for dynamic. Both techniques are non-destructive and independent of knowing the value of Poisson's ratio. We used samples of approximately 5.00 mm diameters, and the influence percentage of HGM additives differed from that of 100%Wt resin. They obtained G values by opting for these composite materials' different methods, showing a maximum deviation of 5.44%. [ABSTRACT FROM AUTHOR]

Herein, we study the London dispersion forces between organic structure directing agents (OSDAs)—here tetraalkyl-ammonium or -phosphonium molecules—and silica zeolite frameworks (FWs). We demonstrate that the interaction energy for these dispersion forces is correlated to the number of H atoms in OSDAs, irrespective of the structures of OSDAs or FWs, and of variations in charges and thermal motions. All calculations considered—DFT-D3 and BOMD undertaken by us, and molecular mechanics from an accessible database—led to the same trend. The mean energy of these dispersion forces is ca. −2 kcal.mol−1 per H for efficient H-O contacts. [ABSTRACT FROM AUTHOR]

Highlights The aim of this study is to numerically investigate the low‐velocity impact behavior of carbon fiber reinforced orthogonal woven fabric composite sandwich structures with five different geometric configurations and four different curve angles. Low velocity impact simulations were performed in LS DYNA finite element program to investigate the effects of core configuration and curve angle on peak contact force, energy absorption efficiency and damage mode. A progressive damage analysis based on the combination of the Hashin damage criterion and the Cohesive Zone Model (CZM) with bilinear traction‐separation law was performed using the MAT‐54 (ENHANCED_COMPOSITE_DAMAGE) material model. Among the five different cores, Trapezoidal core has the highest peak force average of 2.9 kN while Triangular core sandwich structure has the lowest with 1.23 kN. Absorbed energy efficiency average was highest for rectangular core with 0.95 and lowest for sinusoidal core with 0.69. The specific absorbed energy value was highest for Triangular core with 0.312 J/g and lowest for Sinusoidal core with 0.178 J/g. The damage area on the structure increased with increasing curve angle. It was determined that the core structure and curve angle is an effective parameter on peak force and energy absorption efficiency. Impact behavior of sandwich composite structures was examined. The effects of core type and curve angles on peak force, energy absorption efficiency and specific absorption energy were investigated. Specific absorption energy rates were compared with studies in the literature. [ABSTRACT FROM AUTHOR]

Computing the Casimir force and energy between objects is a classical problem of quantum theory going back to the 1940s. Several different approaches have been developed in the literature often based on different physical principles. Most notably a representation of the Casimir energy in terms of determinants of boundary layer operators makes it accessible to a numerical approach. In this paper, we first give an overview of the various methods and discuss the connection to the Krein-spectral shift function and computational aspects. We propose variants of Krylov subspace methods for the computation of the Casimir energy for large-scale problems and demonstrate Casimir computations for several complex configurations. This allows for Casimir energy calculation for large-scale practical problems and significantly speeds up the computations in that case. [ABSTRACT FROM AUTHOR]

The implementation of hot melt adhesives reaching structural adhesion with both impact resistance and detachability is of prospective industry value but still remains challenging. In this work, 2‐amino‐4‐hydroxy‐6‐methylpyrimidine serving as both chain extender and end‐capping reagent due to its isomerism, was developed to construct a supramolecular polyurethane‐derived hot melt structural adhesive. The as‐synthesized PUM elastomers occurs obvious decrease of molecular weight at 80°C compared to room temperature, revealing the existence of self‐complementary 2‐ureido‐4[1H]‐pyrimidinone (UPy) motifs at chain ends. This unique structure allows to chemically incorporate abundant hierarchical and quadruple hydrogen bonding moieties, which results in remarkable enhancement of shear strength, ranging from 6.4 to 16.6 MPa. More importantly, it also exhibits unique impact‐strengthening and reproducible adhering ability. The Hopkinson‐press‐bar and cyclic tensile tests manifest that quadruple hydrogen bonds play a pivotal role in buffering external forces and increasing energy dissipation when exposed to high velocity impacts. The true stress and strain synchronously increase as the strain rate augments while the shear strength can even roar up to ~18 MPa at high tensile speed. With regard to mild synthetic conditions, atomic economic use of reactants, it is promising that this material has industrial potential to be utilized in applications referred to energy‐absorption and reproducible structural adhesion. [ABSTRACT FROM AUTHOR]