关键词： Grain refinement  

摘要： The influence of cryorolling (CYR) on the microstructure, mechanical properties, and formability of heat-treatable (AA 6061) and non heat-treatable (AA 5083) aluminum alloys was investigated. Solutionized (SL) AA 5083 and AA 6061 alloy plates are cryorolled to reduce the thickness from 6.5 to 1 mm (the total true strain of 1.87). Short annealing treatment is performed on cryorolled samples at different temperatures with a fixed annealing time to improve ductility. The effect of annealing temperature on microstructure, mechanical properties, and formability was systemically studied. The results showed grain refinement after CYR with higher dislocation density when compared to the SL condition, and their effect is reflected in the mechanical properties. The limiting dome height test is used in the present work to compare the formability of cryorolled and annealed samples. The formability characteristics correlated well with the strain hardening behavior, which is modeled using the Kocks-Mecking-Estrin (KME) dislocation density model. The dislocation density evolution in the original KME model was modified to consider the contributions of grain size, solutes, and precipitates. The tensile curves predicted from the KME model correlated well with the experimental curves in all the conditions investigated. In addition to that, the predicted dislocation density using the modified KME model agreed well with the dislocation density determined experimentally.

关键词： Thermostimalated luminescence   poly(arylenephthalides)   Chemical kinetics   DFT approximation   Quantum tunneling   Mechanical relaxation  

摘要： Kinetics of thermostimulated luminescence (TSL) of poly(diphenylenephthalide) (PDPh) films has been studied using mathematical modelling and DFT approximation. TSL of PDPh-film was considered to be arising from irradiative deactivation of diphenylene (DP) fragment of polymer chain in excited state formed upon recombination of the spatial separated ion-radical pairs generated by photoexcitation. Two parallel monomolecular transformations leading to excited DP have been revealed: the first path is characterized by the activation parameters of the kinetic rate constant k1 which equal to Al ti 105 sec 1 and Eat ti 70 kJ mol(-1). This path may be interpreted in terms of mechanical relaxation theory by segmental polymer mobility as electron transfer (ET) from phthalide (Ph) anion-to DP cation-radical. The second channel is supposed to be consist of two consecutive ET from triarylmethyl anion-radical to phthalide neutral (A2 ti 1 sec 1, Ea2 ti 20 kJ mol(-1)), and then to DP cation-radical (A3 N 104 sec 1, E,3 N 40 kJ mol(-1)) of the polymer chain indicating y- and fl-relaxation, respectively. The revealed mechanistic steps and electron retention efficiency estimated in B97-2/6-311 + G(d,p) approximation for the most probable anion-radicals may point out the key role of domino quantum tunneling in transfer and recombination of charges in PDPh films.

摘要： Statement of problem. The adhesion properties of modified cement-retained implant prostheses have not been elucidated. Purpose. The purpose of this in vitro study was to compare the adhesion strength and the flow conditions of the adhesives of 3 common modified cement-retained methods (MCRMs). Material and methods. Four cement-retained methods were used: an occlusal hole for screw access (OH), a lingual hole for releasing the excess adhesive (LH), a resin replica for the titanium abutment (RR), and a control group (no holes and no resin trial abutments). Eight zirconia prostheses in each group were processed and cemented. The adhesion strength was examined by mechanical tensile experiments (MTE) in vitro. One-way ANOVA and the LSD post hoc tests were used to compare the results of the MTE (alpha=.05). The flow conditions of adhesives in the adhesion process were analyzed by computational fluid dynamics (CFD). CFD-Post 16.0 (ANSYS, Inc) was used to analyze the results of the CFD analyses. Results. The adhesion strength of each group was 289.3 +/- 37.7 N in the LH group, 281.3 +/- 50.1 N in the OH group, 263.3 +/- 49.3 N in the RR group, and 239.2 +/- 29.4 N in the control group. A statistically significant difference is seen in the adhesion strength between the LH group and the control group (P=.025). The internal filling ratio of adhesives between the groups ranges from high to low in the order the LH group, the OH group, the RR group, and the control group. The amount of cervical overflow of adhesives between the groups ranges from less to more in the order the RR group, the OH group, the LH group, and the control group. Conclusions. MCRMs can effectively reduce the amount of cervical overflow of adhesives and improve the filling condition of the adhesive and its clearance to ensure the adhesion strength of the prostheses.

关键词： Particle resuspension   Aerodynamic disturbances   Surface vibrations   Rough surfaces   Particle surface interaction  

摘要： Particle resuspension in indoor spaces constitutes a concern to human health as it re-introduces deposited particles on surfaces into the bulk air. Resuspension can occur due to indoor human activities causing aerodynamic and mechanical vibration disturbances. The objective of the work is to develop a simplified model that can predict resuspension triggered by the simultaneous action of aerodynamics and vibration forces from hard floor material. The mathematical model was coupled with computational fluid dynamics (CFD) model to predict, through a probabilistic approach, the rates of particle resuspension from indoor surfaces due to indoor activities. The developed model accounted for the reduction of adhesive forces due to vibrations and for the lift and drag forces and moments due to the fluid flow while setting the resuspension condition to predict the resuspension rates. The resuspension model was validated by published literature data on particle resuspension due aerodynamic and mechanical disturbances and good agreement was found. Results: showed that particle resuspension exhibited a rapid burst during the first 25 s of the disturbance before decreasing to negligible values. Resuspension rates also increased when vibrations were accounted for with aerodynamic disturbances. For different indoor surfaces, it was found that resuspension fractions were the smallest for glass surfaces, followed by marble and linoleum. Moreover, resuspension fractions increased by 48.4%, 60.5% and 63% for glass, marble and linoleum when aerodynamic disturbances were accompanied with vibrations. A decrease in surface roughness can increase adhesive forces, and stiffness values reducing the effect of vibrations on enhancing resuspension.

关键词： Intracranial aneurysm   Hemodynamic force   Stretch   Fibroblast   Macrophage  

摘要： Intracranial aneurysm (IA) usually induced at a bifurcation site of intracranial arteries causes a lethal subarachnoid hemorrhage. Currently, IA is considered as a macrophage-mediated inflammatory disease triggered by a high wall shear stress (WSS) on endothelial cells. However, considered the fact that a high WSS can be observed at every bifurcation site, some other factors are required to develop IAs. We therefore aimed to clarify mechanisms underlying the initiation of IAs using a rat model. We found the transient outward bulging and excessive mechanical stretch at a prospective site of IA formation. Fibroblasts at the adventitia of IA walls were activated and produced (C-C motif) ligand 2 (CCL2) as well in endothelial cells loaded on high WSS at the earliest stage. Consistently, the mechanical stretch induced production of CCL2 in primary culture of fibroblasts and promoted migration of macrophages in a Transwell system. Our results suggest that distinct hemodynamic forces, mechanical stretch on fibroblasts and high WSS on endothelial cells, regulate macrophage-mediated IA formation.

关键词： Metallic thermal protection system   Honeycomb sandwich panel   Bayesian regularized neural network   Constrained optimization   Genetic algorithm   Stochastic ranking  

摘要： This paper details the application of the finite element model, Bayesian regularized neural network, and genetic algorithm for metallic thermal protection system parameter optimization. The object is to minimize the structure weight and satisfy multiple performance constraints which consist of the deformation of the top face sheet, the stress around the lug hole, the stress of the honeycomb core, and the inner temperature. Firstly, a high-fidelity thermo-mechanical coupled finite element model was established to investigate the thermal and mechanical properties of the metallic thermal protection system. Then, surrogate models were constructed based on the Bayesian regularized neural network which assigns a probabilistic nature to the network weights and biases and allows the network automatically and optimally penalize complex models. To guarantee full exploration of the design space, an optimal orthogonal-maximin Latin hypercube design was adopted and modified to generate preliminary sampling points. Finally, an approach for genetic algorithm constraint handling, stochastic ranking, was introduced and modified by multiple constraint ranking to handle constraints. In addition, a sensitivity analysis was performed to disclose the effects of individual design variables on the thermal and mechanical responses. The results indicate that the structure mass is decreased by 41.2 % when compared to the initial design and all the constraints are satisfied.

关键词： hydrogels   ideal networks   molecular dynamics   PEG-peptide  

摘要： Simulations of local structure and interactions in stimuli-responsive hydrogel networks at atomistic resolution has the capability to compliment experimental efforts by providing insight into current soft materials design challenges. This work simulates ideal hexafunctional networks of poly(ethylene glycol) (PEG)-diacrylate (PEGDA) and PEG-peptide hydrogels with two enzyme-responsive peptide sequences, Gly-Leu-Lys (GLK) and Gly-Pro-Gln-Gly-Ile-Phe-Gly-Gln-Lys (GPQGIFGQK), using molecular dynamics (MD) simulations at water contents from 84% to 90%. This presents the first atomistic MD study of a PEG-peptide hydrogel. The mesh sizes obtained are compared to common swelling theories and the available micropore space for diffusion is compared to the sizes of a family of matrix metalloproteinases (MMPs) to predict size-based exclusion. The effects of interactions between PEG, peptide, and water on the chemical environment surrounding the cleaving site of peptides are investigated by examining partial radial distribution functions and solvent accessible surface areas. The chemical environment around the peptide sequence is found to be more hydrophobic in PEG-9-peptide hydrogels, thereby favoring cleavage by the hydrophobic binding pocket of MMPs. Furthermore, the mechanical moduli of the hydrogels is also examined, and an increase with the incorporation of peptide sequences and a general decrease with increasing water concentration is observed.

关键词： Young’s modulus   Stress   Compression   Shale   Tensile strength  

摘要： Shale gas has become a major source of gas supply in the United States and is becoming increasingly important worldwide. The key technique for the development is hydraulic fracturing in horizontal wells. Kerogen is the main component of organic matter in shale. It may be the spot of fracture initiation due to its weaker mechanical properties. The measurement of the mechanical properties and failure envelope of kerogen may be a challenge due to small-size kerogen aggregates immersed in shale rocks. In this work, we propose a practical scheme based on molecular dynamics simulations to estimate the elastic and relevant mechanical properties of kerogen for fracturing, including Young's modulus, Poisson's ratio, compressive and tensile strengths, as well as the parameters of the Mohr-Coulomb failure criterion. This work sets the stage to obtain basic kerogen parameters for the simulation of fracturing in shale rocks.

关键词： TiN/VN composite   2NN MEAM potential   Strain rate and temperature effects   Mechanical properties   MD simulation  

摘要： The second nearest-neighbor modified embedded-atom method (2NN MEAM) potential of Ti-V-N ternary system is developed based on the newly optimized interaction potentials of binary systems. The obtained potentials can excellently reproduce the structural, elastic and surface properties of the relevant systems. Then the effects of the strain rate and temperature on the mechanical properties of TiN/VN composite are studied by using the present potentials. It is found that strain rates have almost no influence on the Young's modulus of TiN/VN composite, but have a great influence on the inelastic properties. Whereas both the Young's modulus and the inelastic properties are sensitive to temperature. It is also found that the fracture of TiN/VN composite is a brittle fracture taking place in the VN layers. (C) 2019 Elsevier B.V. All rights reserved.

关键词： mechanotransduction   Piezo1   Piezo2   mechanosensitive ion channel   inactivation   activation   gating  

摘要： Piezo1 ion channels are activated by mechanical stimuli and mediate the sensing of blood flow. Although cryo-electron microscopy (cryo-EM) structures have revealed the overall architecture of Piezo1, the precise domains involved in activation and subsequent inactivation have remained elusive. Here, we perform a targeted chimeric screen between Piezo1 and the closely related isoform Piezo2 and use electrophysiology to characterize their inactivation kinetics during mechanical stimulation. We identify three small subdomains within the extracellular cap that individually can confer the distinct kinetics of inactivation of Piezo2 onto Piezo1. We further show by cysteine crosslinking that conformational flexibility of these subdomains is required for mechanical activation to occur and that electrostatic interactions functionally couple the cap to the extensive blades, which have been proposed to function as sensors of membrane curvature and tension. This study provides a demonstration of internal gating motions involved in mechanotransduction by Piezo1.