Linear Atomic Cluster Expansion Force Fields for Organic Molecules: beyond RMSE

We demonstrate that fast and accurate linear force fields can be built for molecules using the Atomic Cluster Expansion (ACE) framework. The ACE models parametrize the Potential Energy Surface in terms of body ordered symmetric polynomials making the functional form reminiscent of traditional molecular mechanics force fields. We show that the 4 or 5-body ACE force fields improve on the accuracy of the empirical force fields by up to a factor of 10, reaching the accuracy typical of recently proposed machine learning based approaches. We not only show state of the art accuracy and speed on the widely used MD17 and ISO17 benchmark datasets, but also go beyond RMSE by comparing a number of ML and empirical force fields to ACE on more important tasks such as normal mode prediction, high temperature molecular dynamics, dihedral torsional profile prediction and even bond breaking. We also demonstrate the smoothness, transferability and extrapolation capabilities of ACE on a new challenging benchmark dataset comprising a potential energy surface of a flexible drug-like molecule.

Non-uniform model of relationship between surface strain and rust expansion force of reinforced concrete

When operating within the environments rich with sodium chloride, steel bars of reinforced concrete structures are often subject to corrosion caused by surrounding erosive materials, and the associated rust expansion force due to corrosion takes a critical role in determining the durability of relevant reinforced concrete structures. By investigating the corrosion course of steel reinforcement with theory of elasticity, a numerical rust expansion model is established for the moment of concrete surface rupture based on non-uniform sin function. Cuboid reinforced concrete specimen with squared cross sections is tested to analyze the rust expansion when concrete cracks due to corrosive forces. The utility of the established expansion model is validated by numerical simulation with Abaqus through the comparison between the associated outcomes. The impacts of steel bar diameter and concrete cover thickness on the magnitude of rust expansion force are discussed.

The mechanical characteristics and performance evaluation of a newly developed silicone airway stent (GINA stent)

Central airway obstruction (CAO) can be attributed to several benign or malignant conditions. Although surgery is the preferred therapeutic option for the management of CAO, bronchoscopic treatment can be performed in scenarios where the surgical procedure is not possible. Recent years have witnessed several improvements in the field of bronchoscopic treatment, especially with regard to airway stents. Current research involves new attempts to overcome the existing shortcomings pertaining to the stents (migration, mucostasis, and granulation tissue formation). The authors have recently developed a new silicone airway stent (GINA stent) with an anti-migration design, dynamic structure that enables the reduction of stent cross-sectional area, and radio-opacity. The present study aimed to evaluate the mechanical characteristics and performance of the novel GINA stent using a porcine tracheal stenosis model. In the current study, all the tests involved the comparison of the GINA stent [outer diameter (OD, mm): 14; length (L, mm): 55] with the Dumon stent (OD: 14; L: 50). The mechanical tests were performed using a digital force gauge, in order to determine the anti-migration force, expansion force, and flexibility. The present study evaluated the short-term (3 weeks) performance of the two stents after implantation [GINA (n = 4) vs. Dumon (n = 3)] in the porcine tracheal stenosis model. The results pertaining to the comparison of the mechanical properties of the GINA and Dumon stents are stated as follows: anti-migration force (18.4 vs. 12.8 N, P = 0.008); expansion force (11.9 vs. 14.5 N, P = 0.008); and flexibility (3.1 vs. 4.5 N, P = 0.008). The results pertaining to the comparison of the short-term performance of the GINA and Dumon stents are stated as follows: mucus retention (0/4 vs. 0/3); granulation tissue formation (0/4 vs. 0/3); and migration (1/4 vs. 2/3). The GINA stent displayed better mechanical properties and comparable short-term performance, compared to the Dumon stent.

A Statistical Evolution Model of Concrete Damage Induced by Seawater Corrosion

The transmission of sulfate ions in concrete results in formation of calcium sulfoaluminate crystals due to chemical reactions. The expansion of calcium sulfoaluminate crystals is the main cause of concrete corrosion damage. In this study, ultrasonic analysis was used to detect the modulus change of concrete due to sulfate corrosion to obtain the basic law of corrosion damage evolution. An exponential growth model was developed for the internal expansion force based on the chemical reaction rate of calcium sulfoaluminate crystallization. Then, the evolution equation of the number density of microcracks was derived based on their initiation and balance conditions. Finally, a statistical model was developed for the concrete damage evolution by integrating the volume of microcracks. It is shown that the statistical evolution model can well characterize the evolution of concrete corrosion damage.