Phase Dependent Mechanosensitivity in Cardiomyocytes

Cardiomyocytes are mechanosensitive. In the functioning heart, discrete sets of cardiac oscillators maintain stable relative phase dynamics and mechanical coupling between each other through the elastic tissue. A few questions that remains elusive to date are, how strong is the coupling and how tunable is their dynamics, whether this coupling is phase dependent, and if so, at what phase of cardiac dynamics is the coupling most dominant. In other words, at which phase of its dynamics a cardiac cell is most sensitive to forces and deformations induced by its neighbors. Here we address these questions by culturing rat cardiomyocytes on a stretchable substrate. We apply cyclic stretch on the substrate with a range of frequencies in the vicinity of the intrinsic beating frequency of the cell cluster. We find that the cell cluster can synchronize its dynamics with that of the substrate within 25% of its intrinsic frequency in less than a minute. However, it takes much longer time to return to its intrinsic frequency after removal of substrate stretch. With increasing substrate frequency, the cluster tends to catch up, and beats with a range of frequencies between the intrinsic and the applied with wide variation in relative phases. This allows us to measure phase dependent mechano-sensitivity of the cardiac cluster to the periodic deformation of the substrate that is critical to produce stable relative phase dynamics. We find that cardiac cells are most mechano sensitive when they are at 1/2 of their phase. This phase dependence might be mediated by the ion channels active at this phase of the dynamics. This study identifies a functional output of sub-second scale mechanotransduction with the potential to enhance or reinforce cardiac contractile dynamics.

     

Biomechanical and dynamic mechanism of locust take-off

The biomimetic locust robot hopping vehicle has promising applications in planet exploration and reconnaissance. This paper explores the bionic dynamics model of locust jumping by using high-speed video and force analysis. This paper applies hybrid rigid-flexible mechanisms to bionic locust hopping and studies its dynamics with emphasis laid on the relationship between force and jumping performance. The hybrid rigid-flexible model is introduced in the analysis of locust mechanism to address the principles of dynamics that govern locust joints and mechanisms during energy storage and take-off. The dynamic response of the biomimetic mechanism is studied by considering the flexi- bility according to the locust jumping dynamics mechanism. A multi-rigid-body dynamics model of locust jumping is established and analyzed based on Lagrange method; elastic knee and tarsus mechanisms that were proposed in previous works are analyzed alongside the original bionic joint configurations and their machinery principles. This work offers primary theories for take-off dynamics and establishes a theoretical basis for future studies and engineering applications.     

细胞铺展动力学的研究进展

细胞与细胞外基质之间的相互作用在细胞的迁移、分化、凋亡等生理过程中起着重要的作用,细胞铺展作为细胞与细胞外基质作用的第1步,受到了人们的广泛关注.首先阐述了细胞铺展的关键生物动力学过程,对铺展3个不同阶段的特点进行了总结和归纳,并运用力学的观点阐明了细胞铺展的驱动力及驱动机制,详细讨论了聚合力、黏附力以及细胞张力等3种主要作用力在细胞铺展过程中的作用规律以及相应的物理模型.在此基础上,从细胞的黏性流动及力学平衡两个方面出发,简要综述了已有相关研究结果的不足之处,介绍了当前建立细胞铺展动力学模型的主要思路,并探讨了今后面向细胞生物学需求的相关细胞动力学的研究方向.      

Modelling Cardiac Tissue Growth and Remodelling

Cardiac growth and remodelling are key phenomena influencing the physiological performance of the heart and progression of various cardiac diseases. Our basic knowledge of the characteristics of cardiac growth and remodelling have benefitted from the study of the corresponding changes in tissue structure. Computational modelling is capable of integrating multi-scale biological and physiological information of the heart to better delineate the mechanisms underpinning normal physiological and abnormal pathological cardiac processes. In this article, we summarise recent state-of-the-art modelling studies of cardiac growth and remodelling in health and disease, demonstrate the use of finite element modelling approach in simulating growth of an embryonic linear heart tube and towards understanding the roles of structural remodelling in heart failure.     

Analysis of a new simple one dimensional chaotic map

In this paper, a new one-dimensional map is introduced, which exhibits chaotic behavior in small interval of real numbers. It is discovered that a very simple fraction in a square root with one variable and two parameters can lead to a period-doubling bifurcations. Given the nonlinear dynamics of one-dimensional chaotic maps, it is usually seen that chaos arises when the parameter raises up to a value, however in our map, which seems reverse, it arises when the related parameter decreases and approaches to a constant value. Since proposing a new map entails solid foundations, the analysis is originated with linear stability analysis of the new map, finding fixed points. Additionally, the nonlinear dynamics analysis of the new map also includes cobweb plot, bifurcation diagram, and Lyapunov analysis to realize further dynamics. This research is mainly consisting of real numbers, therefore imaginary parts of the simulations are omitted. For the numerical analysis, parameters are assigned to given values, yet a generalized version of the map is also introduced.     

Computational Mechanics of the Heart

Finite elasticity theory combined with finite element analysis provides the framework for analysing ventricular mechanics during the filling phase of the cardiac cycle, when cardiac cells are not actively contracting. The orthotropic properties of the passive tissue are described here by a “pole–zero” constitutive law, whose parameters are derived in part from a model of the underlying distributions of collagen fibres. These distributions are based on our observations of the fibrous-sheet laminar architecture of myocardial tissue. We illustrate the use of high order (cubic Hermite) basis functions in solving the Galerkin finite element stress equilibrium equations based on this orthotropic constitutive law and for incorporating the observed regional distributions of fibre and sheet orientations. Pressure–volume relations and 3D principal strains predicted by the model are compared with experimental observations. A model of active tissue properties, based on isolated muscle experiments, is also introduced in order to predict transmural distributions of 3D principal strains at the end of the contraction phase of the cardiac cycle. We end by offering a critique of the current model of ventricular mechanics and propose new challenges for future modellers. This revised version was published online in July 2006 with corrections to the Cover Date.     

A simple model for myocardial changes in a failing heart

In a simplified setting, a multi-network model for remodeling in the left ventricle (LV) is developed that can mimic various pathologies of the heart. The model is an extension of the simple model introduced by Nardinocchi and Teresi [9], Nardinocchi et al. [10], [11] that results in an algebraic relation for LV pressure–volume–contraction. We considered two networks, the original tissue and a new tissue, each of which has its own volume fraction, stress-free reference configuration, elastic properties, and contractility. This is used to explore the consequences of microstructural changes in the muscle tissue on LV function in terms of the pressure–volume loop during a single cardiac cycle. Special attention is paid to the stroke volume, which is directly related to cardiac output, and changes in LV wall stress caused by various disease states, including wall thinning (dilated cardiomyopathy), wall thickening (hypertrophic cardiomyopathy), contractility degradation, and stiffness changes (scarring). Various scenarios are considered that are of clinical relevance, and the extent and nature of remodeling that could lead to heart failure are identified.     

梯度纳米结构金属力学性能、变形机理和多尺度计算研究进展

近年来,梯度纳米结构金属因其优越的力学性能和独特的塑性变形机理受到广泛关注,已成为材料与力学学科的热点和前沿。本文首先介绍梯度纳米结构金属的强度、塑性、加工硬化和抗疲劳等核心力学性能,以及晶粒长大、塑性应变梯度和几何必需位错等塑性变形机理及其力学研究。其次介绍梯度纳米结构金属的多尺度计算与模拟研究。最后讨论梯度纳米结构金属研究领域存在的挑战。     

On trailing vortices: A short review

This paper reviews some mechanisms involved in the dynamics of vortices in fluid flows. The topic is first introduced by pointing out its importance in aerodynamics. Several basic notions useful to appraise experimental observations are then surveyed, namely: centrifugal instabilities, inertial waves, cooperative instabilities, vortex merger, vortex breakdown and turbulence in vortices. Each topic is illustrated with experimental or numerical results.     

High-order DG solvers for underresolved turbulent incompressible flows: A comparison of L2 and H(div) methods

The accurate numerical simulation of turbulent incompressible flows is a challenging topic in computational fluid dynamics. For discretisation methods to be robust in the underresolved regime, mass conservation and energy stability are key ingredients to obtain robust and accurate discretisations. Recently, two approaches have been proposed in the context of high-order discontinuous Galerkin (DG) discretisations that address these aspects differently. On the one hand, standard L²-based DG discretisations enforce mass conservation and energy stability weakly by the use of additional stabilisation terms. On the other hand, pointwise divergence-free H(div)-conforming approaches ensure exact mass conservation and energy stability by the use of tailored finite element function spaces. This work raises the question whether and to which extent these two approaches are equivalent when applied to underresolved turbulent flows. This comparative study highlights similarities and differences of these two approaches. The numerical results emphasise that both discretisation strategies are promising for underresolved simulations of turbulent flows due to their inherent dissipation mechanisms.     

金属材料辐照缺陷演化的分子动力学研究进展

辐照条件下,高能粒子在金属材料内部引入稠密的辐照缺陷,导致材料力学性能严重退化,缩短材料服役寿命,是辐照材料研究的关键问题。辐照缺陷多处在纳米尺度,故分子动力学方法是模拟辐照缺陷的有力工具,近年来被广泛用于研究辐照缺陷演化。本文总结了金属材料中辐照缺陷演化的分子动力学研究进展,介绍了级联碰撞、点缺陷、空洞、氦泡、Frank位错环、层错四面体等辐照缺陷,及其与位错、晶界等微结构的相互作用。分子动力学方法揭示的机制与模型,深化了学界对辐照效应的认识,有助于提高辐照材料力学性能和设计耐辐照材料。     

金属材料辐照缺陷演化的分子动力学研究进展

辐照条件下,高能粒子在金属材料内部引入稠密的辐照缺陷,导致材料力学性能严重退化,缩短材料服役寿命,是辐照材料研究的关键问题。辐照缺陷多处在纳米尺度,故分子动力学方法是模拟辐照缺陷的有力工具,近年来被广泛用于研究辐照缺陷演化。本文总结了金属材料中辐照缺陷演化的分子动力学研究进展,介绍了级联碰撞、点缺陷、空洞、氦泡、Frank位错环、层错四面体等辐照缺陷,及其与位错、晶界等微结构的相互作用。分子动力学方法揭示的机制与模型,深化了学界对辐照效应的认识,有助于提高辐照材料力学性能和设计耐辐照材料。     

Perspectives on biomechanical growth and remodeling mechanisms in glaucoma

Glaucoma is a blinding diseases in which damage to the axons results in loss of retinal ganglion cells. Experimental evidence indicates that chronic intraocular pressure elevation initiates axonal insult at the level of the lamina cribrosa. The lamina cribrosa is a porous collagen structure through which the axons pass on their path from the retina to the brain. Recent experimental studies revealed the extensive structural changes of the lamina cribrosa and its surrounding tissues during the development and progression of glaucoma. In this perspective paper we review the experimental evidence for growth and remodeling mechanisms in glaucoma including adaptation of tissue anisotropy, tissue thickening/thinning, tissue elongation/shortening and tissue migration. We discuss the existing predictive computational approaches that try to elucidate the potential biomechanical basis of theses growth and remodeling mechanisms and highlight open questions, challenges, and avenues for further development.     

非线性随机动力学与控制的哈密顿理论框架

 近几年来，笔者提出与发展了随机激励的耗散的哈密顿系统理 论，包括精确平稳解、等效非线性系统法、拟哈密顿系统随机平均法、 拟哈密顿系统的随机稳定性与随机分岔、首次穿越损坏分析方法及非 线性随机最优控制策略，从而构成了一个非线性随机动力学与控制的 哈密顿理论框架.本文简要介绍这一理论框架.     

Intermittent neural synchronization in Parkinson’s disease

Motor symptoms of Parkinson’s disease are related to the excessive synchronized oscillatory activity in the beta frequency band (around 20 Hz) in the basal ganglia and other parts of the brain. This review explores the dynamics and potential mechanisms of these oscillations employing ideas and methods from nonlinear dynamics. We present extensive experimental documentation of the relevance of synchronized oscillations to motor behavior in Parkinson’s disease, and we discuss the intermittent character of this synchronization. The reader is introduced to novel time-series analysis techniques aimed at the detection of the fine temporal structure of intermittent phase locking observed in the brains of Parkinsonian patients. Modeling studies of brain networks are reviewed, which may describe the observed intermittent synchrony, and we discuss what these studies reveal about brain dynamics in Parkinson’s disease. The Parkinsonian brain appears to exist on the boundary between phase-locked and nonsynchronous dynamics. Such a situation may be beneficial in the healthy state, as it may allow for easy formation and dissociation of transient patterns of synchronous activity which are required for normal motor behavior. Dopaminergic degeneration in Parkinson’s disease may shift the brain networks closer to this boundary, which would still permit some motor behavior while accounting for the associated motor deficits. Understanding the mechanisms of the intermittent synchrony in Parkinson’s disease is also important for biomedical engineering since efficient control strategies for suppression of pathological synchrony through deep brain stimulation require knowledge of the dynamics of the processes subjected to control.     

Robust control of flexible-joint robots using voltage control strategy

So far, control of robot manipulators has frequently been developed based on the torque-control strategy. However, two drawbacks may occur. First, torque-control laws are inherently involved in complexity of the manipulator dynamics characterized by nonlinearity, largeness of model, coupling, uncertainty and joint flexibility. Second, actuator dynamics may be excluded from the controller design. The novelty of this paper is the use of voltage control strategy to develop robust tracking control of electrically driven flexible-joint robot manipulators. In addition, a novel method of uncertainty estimation is introduced to obtain the control law. The proposed control approach has important advantages over the torque-control approaches due to being free of manipulator dynamics. It is computationally simple, decoupled, well-behaved and has a fast response. The control design includes two interior loops; the inner loop controls the motor position and the outer loop controls the joint position. Stability analysis is presented and performance of the control system is evaluated. Effectiveness of the proposed control approach is demonstrated by simulations using a three-joint articulated flexible-joint robot driven by permanent magnet dc motors.     

高速机构动力学研究进展

高速机械动力学及其控制是机构学研究领域的一个前沿性学科,与其内容相关者涉及多个新兴学科领域.本文首先概述了高速机构动力学基础------柔性多体动力学建模理论及周期时变机械系统动力行为研究的现状及其进展状况.其次,对机械工程中常见的典型高速机构,特别是对高速连杆、凸轮机构动力学的研究现状进行了分门别类的介绍.再次,对带间隙机构动力学的研究给予了一定的关注.相应地,对柔性机构振动主动控制的研究状况也进行了简要介绍.最后,指出上述研究领域内一些值得研究的问题.      

A divide and conquer algorithm for constrained multibody system dynamics based on augmented Lagrangian method with projections-based error correction

This paper presents a?new parallel algorithm for dynamics simulation of general multibody systems. The developed formulations are iterative and possess divide and conquer structure. The constraints equations are imposed at the acceleration level. Augmented Lagrangian methods with mass-orthogonal projections are used to prevent from constraint violation errors. The proposed approaches treat tree topology mechanisms or multibody systems which contain kinematic closed loops in a?uniform manner and can handle problems with rank deficient Jacobian matrices. Test case results indicate good accuracy performance dependent on the expense put in the iterative correction of constraint equations. Good numerical properties and robustness of the algorithms are observed when handling systems with single and coupled kinematic loops, redundant constraints, which may repeatedly enter singular configurations.     

Multi-scale HPC system for multi-scale discrete simulation—Development and application of a supercomputer with 1 Petaflops peak performance in single precision

A supercomputer with 1.0 Petaflops peak performance in single precision, designed and established by Institute of Process Engineering, Chinese Academy of Sciences, is introduced in this brief communication. A designing philosophy utilizing the similarity between hardware, software and the problems to be solved is embodied, based on the multi-scale method and discrete simulation approaches developed at Institute of Process Engineering (IPE) and implemented in a graphic processing unit (GPU)-based hybrid computing mode. The preliminary applications of this machine in areas of multi-phase flow, molecular dynamics and so on are reported, demonstrating the supercomputer as a paradigm of green computation in new architecture.