关键词： Secretion clearance   mathematical model   dynamic characteristics   experiments   simulation  

摘要： Secretions in the airways of mechanical ventilated patients are extremely dangerous to patients' health. In recent studies, the continuous constant airflow is adopted, however, it is not consistent with a clinical situation. To study respiratory airflow dynamic characteristics with secretion in the airways, a mathematical model based on clinical mechanical ventilation is established in this paper. To illustrate the secretion's influence on the airflow dynamics of mechanical ventilated respiratory system, three key parameters which are cross section area ratio of secretion/ pipe, air-secretion contact area, and secretion viscosity are involved in the study. Through the experimental study, the accuracy and dependability of the model are confirmed. By the simulation study, we find that: based on the model which combines two airways and two model lungs, when one of the airways was covered with secretion, the maximum pressure of the model lung which is attached to the end of this airway maintains constant when the cross section area ratio is less than 66 percent, and then it tends to decline sharply with the ratio increasing, but it remains constant with the augment of air-secretion contact area, the maximum flow declines both with the increasing of cross section area ratio and air-secretion contact area. Furthermore, as for the other airway, the maximum pressure of the model lung has no significant changes with the augment of area ratio and air-secretion contact area, however, along with the increasing of area ratio and air-secretion contact area, the maximum flow rises up. Moreover, the secretion viscosity has barely any influence on airflow dynamics. According to our analysis results, we conclude that the cross section area ratio of secretion/pipe has bigger influence on airflow dynamic characteristics than air-secretion contact area and secretion viscosity. This paper lays the foundation for the further study of efficacy and safety in mechanical ventilation and the s

关键词： Cu-W interface   Dislocations   Stress-strain behavior  

摘要： Molecular dynamics simulations reveal that compared with Cu, the Cu/W interface with the Kurdjumov-Sachs relationship possesses higher critical strength in the [1 1 (2) over bar](Cu) or [(1) over bar 1 0](Cu) direction and much lower strength in the [1 1 1](Cu) direction, while its ductility is smaller, mainly due to constraints of the interface and W lattice. The evolution of Shockley partial dislocations of Cu/W interface has a strong correlation with the direction of tensile loading, and three edge dislocations appear in the [1 1 1](Cu) direction, while two and one mixed dislocations in the [1 1 (2) over bar](Cu) and [(1) over bar 1 0](Cu) directions, respectively. The obtained results are discussed and compared to provide a deep understanding of the stress-strain behavior and dislocation evolution of the Cu/W interface.

关键词： Electric vehicle   electric differential power steering   robust control   H-2/H-infinity control   mu-synthesis  

摘要： This paper presents a coupling control strategy of force and displacement for an electric differential power steering (EDPS) system to improve steering maneuverability and handling stability of electric vehicles with motorized wheels. In order to investigate mutual influences between vehicles and drivers, models of the EDPS system, the vehicle, the tire as well as the actuate motor are introduced. Then, by analyzing key factors that affect the interaction between vehicles and drivers, the optimum hand wheel torque of the EDPS system is developed and actualized by torque difference between two front wheels based on the H-2/H-infinity control method. In addition, a yaw rate control method is schemed to diminish the yaw moment interference to vehicles caused by the torque difference between two front wheels, and mu-synthesis theory is applied here to improve the yaw rate tracking performance as well as attenuate influences of system uncertainties and disturbances. Finally, simulations by MATLAB/Simulink and hardware-in-the-loop experiments based on dSPACE are conducted and effectiveness of the proposed control strategy is demonstrated by simulation and experiment results and numerical analyses.

关键词： bilayer graphene   mechanical properties   stress-strain   fracture toughness   strain rate  

摘要： Graphene is one of the most important nanomaterials. The twisted bilayer graphene shows superior electronic properties compared to graphene. Here, we demonstrate via molecular dynamics simulations that twisted bilayer graphene possesses outstanding mechanical properties. We find that the mechanical strain rate and the presence of cracks have negligible effects on the linear elastic properties, but not the nonlinear mechanical properties, including fracture toughness. The "two-peak" pattern in the stress-strain curves of the bilayer composites of defective and pristine graphene indicates a sequential failure of the two layers. Our study provides a safe-guide for the design and applications of multilayer grapheme-based nanoelectronic devices.

关键词： MD simulations   PMMA/DBP   Miscibility   Glass transition temperature   Mechanical properties  

摘要： Polymethyl methacrylate (PMMA) and dibutyl phthalate (DBP) binary system was simulated by molecular dynamics (MD) simulations with the COMPASS force field to predict properties of PMMA/DBP blends such as the miscibility, the glass transition temperature (T-g) and mechanical properties of polymer/plasticizer blends. Results show that PMMA/DBP is a miscible system, which can be predicted by comparing the difference of the solubility parameters value (vertical bar Delta delta vertical bar<2.0 MPa0.5) between PMMA and DBP. The free volumes (V-F) and density (rho) of PMMA/DBP system were simulated to study the T-g. It is found that the V-F and rho of PMMA/DBP change regularly along with the increase of DBP mass fraction and the transition occurred at the turning point. We also predicted the effects of temperature and DBP on the mechanical properties of PMMA including Young's modulus (E), Bulk modulus (K), Shear modulus (G) and Poisson's ratio (v). The mechanical properties can be effectively improved by the temperature and the addition of DBP plasticizer, which may provide a more flexible mixture with a lower E, K, G and an increased ductility. Accordingly, the method used in this work is not only a useful tool to provide properties of a given polymer/plasticizer blend but also a promising technique to help screen the formulations of polymer bonded explosive (PBX) and propellants before experiments. (C) 2018 Elsevier Inc. All rights reserved.

关键词： slide-ring polymer   dynamic properties   chain sliding  

摘要： Through coarse-grained molecular dynamics simulation, we have successfully designed the chemically cross-linked (fixed junction) and the slide-ring (SR) systems. Firstly, we examine the dynamic properties such as the mean-square displacement, the bond, and the end-to-end autocorrelation functions as a function of the cross-linking density, consistently pointing out that the SR system exhibits much lower mobility compared with the fixed junction one at the same cross-linking density. This is further validated by a relatively higher glass transition temperature for the SR system compared with that of the fixed junction one. Then, we calculated the effect of the cross-linking density on the stretch-recovery behavior for the SR and fixed junction systems. Although the chain orientation of the SR system is higher than that of the fixed-junction system, the tensile stress is smaller than the latter. We infer that much greater chain sliding can occur during the stretch, because the movable ring structure homogeneously sustains the external force of the SR system, which, therefore, leads to much larger permanent set and higher hysteresis during the recovery process compared with the fixed-junction one. Based on the stretch-recovery behavior for various cross-linking densities, we obtain the change of the hysteresis loss, which is larger for the SR system than that of the fixed junction system. Lastly, we note that the relatively bigger compressive stress for the SR system results from the aggregation of the rigid rings compared with the fixed junction system. In general, compared with the traditionally cross-linked system, a deep molecular-level insight into the slide-ring polymer network is offered and thus is believed to provide some guidance to the design and preparation of the slide-ring polymer network with both good mechanical and damping properties.

摘要： We consider mechanical systems for which the matrices of second partial derivatives of the potential energies at equilibria have zero eigenvalues. It is assumed that their potential energies are holomorphic functions in these singular equilibrium states. For these systems, we prove the existence of proper bounded (for positive time) solutions of the Newton equations of motion convergent to equilibrium in the infinite-time limit. These results are applied to the Coulomb systems of three point charges with singular equilibrium in a line.

关键词： Swarm system   multi-agent system   mechanical system   constraint   adaptive robust control  

摘要： We consider an artificial swarm system consisting of multiple agents. The agents influence each other through the attraction/repulsion, which is related to the relative positions among them. Here the collective behavior of the agents mimics some biological swarm systems. The dynamic model for each agent is built by taking the uncertainty into account. Based on the dynamic model, we propose three types adaptive robust controls, including switching type, non-switching type and fractional type, for each agent. The control design weaves together several intrinsic features of kinematics, dynamics, d'Alembert's principle, constraint, and uncertainty.

关键词： Radiobiological models   Cell surviving fractions   Full-effect plots   Radiation damage repair   Michaelis-Menten enzyme catalysis   Pool molecules for repair  

摘要： Recently, the Euler T and Lambert W transcendental functions found useful applications in cellular radiobiology. Specifically, these functions appeared in mathematical modeling of cell survival after irradiation using the formalism of chemical kinetics. An example is a mechanistic inclusion of cell repair through enzyme catalysis in the Michaelis-Menten formalism, where the concentration of radiation lesions is given by the Lambert function. This function also appears in cell surviving fractions in an alternative aspect of chemical kinetics when lesion repair is carried out by the so-called pool repair molecules without passing through enzyme catalysis. Moreover, even with no reference to chemical kinetics at all, both the Lambert and Euler functions emerge in the framework of the cell repair dynamics described by delayed differential equations. The Euler function is also encountered within the cell blocking mechanism of damage repair in analogy with the counting coincidence correction for the dead time of the radiation detecting instruments. Presently, we analyze the overall usefulness of the Lambert and Euler functions in radiotherapy with a goal of motivating a further exploration of this analytical methodology in mechanistic radiobiological models for cell survival. The main reason for pursuing this pathway is in its unified mechanistic concept of cell surviving fractions valid at all doses from low through intermediate to high radiation exposures. With this advance, no artificial cut-off doses are needed any longer for empirical connections of the intermediate and high dose regimens in mathematical modelings. This is particularly important in radiotherapy because the clinically most frequently used linear-quadratic model is inadequate at high doses. High doses are of main relevance to stereotactic radiotherapy for treatment of localized tumors by efficaciously administering relatively large doses per fraction in a small number of fractions within only a few day

关键词： steered molecular dynamics   point mutation   breast cancer   stiffness   protein stability  

摘要： E-cadherin is a member of the cadherin family that plays a key role in the formation of cell-cell adhesion among epithelial tissues. Point mutations are one of the structural abnormalities of E-cadherin in human carcinomas. Such abnormalities can alter mechanical properties of proteins that play an important role in their biological activities. To determine the impact of point mutations on protein mechanical properties, the second fragment of extracellular domain of E-cadherin was modeled using steered molecular dynamics simulations. The molecular dynamics modeling included application of tensile forces in both constant velocity and constant force modes to examine the effects of Met282 to Ile and Asn315 to Ser mutations on mechanical behavior of protein structure. The stabilities of the wild type and mutant structures were also obtained by the protein design foldX algorithm. Results confirmed the lower stability of the mutant domains compared to the wild type. The mutated proteins displayed softer behavior than the reference protein and their stiffness decreased by up to 34%. Our findings suggest that local changes in molecular structure due to mutations may lead to noticeable alterations in mechanical properties within the entire domain. Since the function of protein is related to its structure, these changes may influence the function of the protein.