关键词： Trabeculae   Relaxation   Myofiber   Modeling   Biomechanics  

摘要： Rapid myocardial relaxation is essential in maintaining cardiac output, and impaired relaxation is an early indicator of diastolic dysfunction. While the biochemical modifiers of relaxation are well known to include calcium handling, thin filament activation, and myosin kinetics, biophysical and biomechanical modifiers can also alter relaxation. We have previously shown that the relaxation rate is increased by an increasing strain rate, not a reduction in afterload. The slope of the relaxation rate to strain rate relationship defines Mechanical Control of Relaxation (MCR). To investigate MCR further, we performed in vitro experiments and computational modeling of preload-adjustment using intact rat cardiac trabeculae. Trabeculae studies are often performed using isometric (fixed-end) muscles at optimal length (Lo, length producing maximal developed force). We determined that reducing muscle length from Lo increased MCR by 20%, meaning that reducing preload could substantially increase the sensitivity of the relaxation rate to the strain rate. We subsequently used computational modeling to predict mechanisms that might underlie this preload-dependence. Computational modeling was not able to fully replicate experimental data, but suggested that thin-filament properties are not sufficient to explain preloaddependence of MCR because the model required the thin-filament to become more activated at reduced preloads. The models suggested that myosin kinetics may underlie the increase in MCR at reduced preload, an effect that can be enhanced by force-dependence. Relaxation can be modified and enhanced by reduced preload. Computational modeling implicates myosin-based targets for treatment of diastolic dysfunction, but further model refinements are needed to fully replicate experimental data.

关键词： PBX interface   Uniaxial tension   Microstructure evolution   Mechanical properties   Failure mechanism  

摘要： Polymer bonded explosives (PBX) are kind of particulate-reinforced composite materials in which interface interaction is of great significance to its structural and mechanical features. In this work, effect of temperature and strain rate on the microstructure, mechanical properties and fracture damage mechanism of TATB-F2314 are studied using molecular dynamics simulations. The TATB layers at the TATB-F2314 interface are deformed, leading to a rough and undulate surface that facilitates the formation hydrogen bonds between TATB and F2314. Intermixing phase is characterized for the first time at the TATB-F2314 interface. The interfacial structures and mechanical properties of TATB-F2314 depend strongly on temperature and strain rate. F2314 experiences a ductile-to-brittle transition at its glass transition temperature, which exerts great influence on the structural evolution and failure mechanism of TATB-F2314. The fracture mainly appears on F2314 under a quasi-static or low strain rate tension but transfers to TATB layers near to the interfacial intermixing phase at a high strain rate. Our simulations reveal the effect of temperature and strain rate on the microstructure, mechanical behavior and fracture damage mechanism of TATBF2314 interface, which is useful for the design, preparation and safe use of PBX.

关键词： piezoelectric   foam   hierarchical   self-powered   sensor  

摘要： With the rapid development of wearable electronics, piezoelectric materials have received great attention owing to their potential solution to the portable power source. To enhance the output capability and broaden the application, it is highly desired for the design of piezoelectric materials with a three-dimensional and porous structure to facilitate strain accumulation. Herein, enlightened by hierarchical structures in nature, a hierarchically nested network was constructed in polyvinylidene fluoride (PVDF) foam via solid-state shear milling and salt-leaching technology. The as-prepared foam exhibited two hierarchical levels of pores with diameters of 20 similar to 50 mu m and 0.3 similar to 4 mu m, by which the porosity and flexibility were significantly enhanced, while the highest piezoelectric output reached 11.84 V and 217.78 nA. As a proof-of-concept, the PVDF piezoelectric foam can also be used to monitor human movement toward the different magnitude of strain and frequency, and simultaneously collect energy in a multidimensional stress field for energy harvesting. This work provides a simple and convenient design idea for the preparation of energy harvesters, which have great application potential as a mechanical energy harvester or self-powered sensor in wearable electronic devices.

关键词： Checkpoint inhibitors   Cancer immunotherapy   Tumor heterogeneity   Receptor dynamics   Virtual patients   PD-1   PD-L1   Cytotoxic T cells   Non-tumor immune cells   Immunological synapse  

摘要： Tumors have developed multitude of ways to evade immune response and suppress cytotoxic T cells. Programed cell death protein 1 (PD-1) and programed cell death ligand 1 (PD-L1) are immune check-points that when activated, rapidly inactivate the cytolytic activity of T cells. Expression heterogeneity of PD-L1 and the surface receptor dynamics of both PD-1 and PD-L1 may be important parameters in modulating the immune response. PD-L1 is expressed on both tumor and non-tumor immune cells and this differential expression reflects different aspects of anti-tumor immunity. Here, we developed a mechanistic computational model to investigate the role of PD-1 and PD-L1 dynamics in modulating the efficacy of PD-1 and PD-L1 blocking antibodies. Our model incorporates immunological synapse restricted interaction of PD-1 and PD-L1, basal parameters for receptor dynamics, and T cell interaction with tumor and non-tumor immune cells. Simulations predict the existence of a threshold in PD-1 expression above which there is no efficacy for both anti-PD-1 and anti-PD-L1. Model also predicts that anti-tumor response is more sensitive to PD-L1 expression on non-tumor immune cells than tumor cells. New combination strategies are suggested that may enhance efficacy in resistant cases such as combining anti-PD-1 with a low dose of anti-PD-L1 or with inhibitors of PD-L1 recycling and synthesis. Another combination strategy suggested by the model is the combination of anti-PD-1 and anti-PD-L1 with enhancers of PD-L1 degradation rate. Virtual patients are then generated to test specific biomarkers of response. Intriguing predictions that emerge from the virtual patient simulations are that PD-1 blocking antibody results in higher response rate than PD-L1 blockade and that PD-L1 expression density on non-tumor immune cells rather than tumor cells is a predictor of response. (C) 2021 Elsevier Ltd. All rights reserved.

关键词： Fe-Cr alloys   Oxidation   EBSD   Micro-cantilever test   Fracture toughness  

摘要： The present study involved a range of iron-chromium (0-20 wt% Cr) alloys of similar crystallographic texture. The oxidation kinetics reduced remarkably when Cr content was 12 wt%. This coincided with the reduction in the number (from three to two) of clearly distinguishable oxide layers. Though the outer hematite (Fe2O3) layer remained, the inner chromite (FeCr2O4, spinel structure) transformed to chromic oxide ((Fe,Cr)(2)O-3, corundum structure) and the columnar coarse grained magnetite (Fe3O4) middle layer disappeared. The chromic oxide displayed higher hardness and increased compressive residual (Raman) stresses. It also showed significantly higher fracture toughness in micro-cantilever bending tests. A clear picture of oxidation resistance, in high-Cr alloys, through phase transformation and associated mechanical integrity of the inner oxide layer thus emerged. (C) 2021 Elsevier B.V. All rights reserved.

关键词： Nanoscratching   CoCrFeMnNi HEA   Friction coefficient   Mechanical properties  

摘要： In this study, molecular dynamics is used to examine mechanical properties and microstructure evolution of nanocrystalline high-entropy alloy (CoCrFeMnNi) under nanoscratching load. Special attentions are paid to the effects of crystal structure, temperature, grain size and twin boundary spacing on the deformation mechanisms and microstructure evolution. The P-h curves show that the maximum indentation force is in reduced order with single-crystal, nanotwin polycrystalline and polycrystalline structures. Specifically, for the single-crystal structure, the amorphization caused by the increment of temperature hinders the movements of dislocations and stacking faults. For the polycrystalline and nanotwin polycrystalline structures, the inverse Hall?Petch relation is observed due to that the interaction between the dislocations and grain boundary (GB) / twin boundary (TB). For the nanotwin polycrystalline structure, the migration of twin boundary is observed during the process of nanoindentation. Furthermore, Hirth and Lomer-Cottrell dislocation locks, secondary twins and FCC?HCP phase transformation are also found in simulations. ? 2021 Elsevier B.V. All rights reserved.

关键词： Manganese peroxidase   DFT calculations   Catalytic mechanism   Oxidation pathway   Single-electron transfer mechanism  

摘要： In this study, manganese peroxidase (MnP) was applied to induce the in vitro oxidation of sulfamethoxazole (SMX). The results indicated that 87.04% of the SMX was transformed and followed first-order kinetics (kobs = 0.438 h-1) within 6 h when 40 U L-1 of MnP was added. The reaction kinetics were investigated under different conditions, including pH, MnP activity, and H2O2 concentration. The active species Mn3+ was responsible for the oxidation of SMX, and the Mn3+ production rate was monitored to reveal the interaction among MnP, Mn3+, and SMX. By integrating the characterizations analysis of the MnP/H2O2 system with the density functional theory (DFT) calculations, the proton-coupled electron transfer (PCET) process dominated the catalytic circle of MnP and the transformation of Mn3+. Additionally, possible oxidation pathways of SMX were proposed based on single-electron transfer mechanism, which primarily included the S-N bond cleavage, the C-S bond cleavage, and one electron loss without bond breakage. It was then transformed to hydrolysis, N-H oxidation, self-coupling, and carboxylic acid coupling products. This study provides insights into the atomic-level mechanism of MnP and the transformation pathways of sulfamethoxazole, which lays a significant foundation for the potential of MnP in wastewater treatment applications.

关键词： Chemical structure   Molecular structure   Organic polymers   Nucleic acid structure   Polymers  

摘要： Although thermosetting resins have good physical and chemical stabilities, their deformation ability is limited and fatigue fracture can easily occur. To overcome the defects of thermosetting resins, we propose introducing an aromatic heterocyclic helical macromolecule chain into a thermosetting resin-cross-linked network. The effect of the helical structure on the thermomechanical properties of the thermosetting resincured system is quantitatively and qualitatively analyzed using a molecular dynamics method. Results show that the helical structure can affect the mechanical properties of the thermosetting resin-cross-linked system along the pitch direction. The introduction of a helical macromolecule chain reduces the density of the cross-linking points and weakens the heat resistance of the cured system to some extent;however, the influence is insignificant. Nevertheless, we are expected to gain some deep insights into the directional control of the mechanical properties of the resin-curing system and microstructure of the cross-linking network by introducing a helical structure.

关键词： molecular dynamics(MD)simulation   microstructure-based constitutive model   high entropy alloy(HEA)   deformation behavior  

摘要： High entropy alloys(HEAs)attract remarkable attention due to the excellent mechanical ***,the origins of their high strength and toughness compared with those of the traditional alloys are still hardly ***,using a microstructure-based constitutive model and molecular dynamics(MD)simulation,we investigate the unique mechanical behavior and microstructure evolution of FeCoCrNiCu HEAs during the *** to the interaction between the dislocation and solution,the high dislocation density in FeCoCrNiCu leads to strong work *** slip systems are stimulated,leading to the good plasticity of *** plastic deformation of FeCoCrNiCu is basically affected by the motion of dislocation *** prismatic dislocation loops inside FeCoCrNiCu are formed by the dislocations with the Burgers vectors of a/6[112]and a/6[112],which interact with each other,and then emit along the<111>slip *** addition,the mechanical properties of FeCoCrNiCu HEA can be predicted by constructing the microstructure-based constitutive model,which is identified according to the evolution of the dislocation density and the stress-strain *** dislocation strengthening and remarkable lattice distortion strengthening occur in the deformation process of FeCoCrNiCu,and improve the ***,the origins of high strength and high toughness in FeCoCrNiCu HEAs come from lattice distortion strengthening and the more activable slip systems compared with *** results accelerate the discovery of HEAs with excellent mechanical properties,and provide a valuable reference for the industrial application of HEAs.

关键词： MATLAB   机器人   动力学方程  

摘要： 运用MATLAB软件的符号函数工具箱,编写了用于计算平面任意多连杆机器人动力学方程的程序,以七连杆机器人为例,计算得出七连杆机器人的动力学公式,并作了数值仿真。该方法简便、高效,与现代计算机技术的发展契合,可以实现任意多连杆平面机器人的建模,也为后续的机器人控制提供了参考依据。