考虑电机绕组特性的柔性机械臂动力学建模

针对柔性机械臂运动中存在的形变现象进行柔性体动力学建模,引入耗散能描述轴承间黏性阻尼,引入关节等效形变描述关节柔性,引入模态假设法描述连杆柔性,引入电机绕组特性描述电机驱动力矩并通过拉格朗日方程建立动力学方程;对模型进行仿真求解,计算出不同传动比和附加重量质心工况下连杆末端的形变,通过对比分析求得连杆末端形变与传动比和附加重量质心之间的关系,为后期机械臂设计优化提供理论基础。     

Very large scale simulations of materials failure

With present-day supercomputers, simulation is becoming a powerful tool for providing immediate insights into the nature of fracture dynamics. Atomistic simulations yield ab initio information about crack-tip formation and deformation at length-scales unattainable by experimental measurement and unpredictable by continuum elasticity theory. We will describe several atomistic dynamics studies concerning brittle fracture and ductile deformation.     

Excitation saturation in two-photon fluorescence correlation spectroscopy

Fluorescence correlation spectroscopy (FCS) has become a powerful and sensitive research tool for the study of molecular dynamics at the single-molecule level. Because photophysical dynamics often dramatically influence FCS measurements, the role of various photophysical processes in FCS measurements must be understood to accurately interpret FCS data. We describe the role of excitation saturation in two-photon fluorescence correlation measurements. We introduce a physical model that characterizes the effects of excitation saturation on the size and shape of the two-photon fluorescence observation volume and derive a new analytical expression for fluorescence correlation functions that includes the influence of saturation. With this model, we can accurately describe both the temporal decay and the amplitude of measured fluorescence correlation functions over a wide range of illumination powers.     

Rule-based modelling and simulation of biochemical systems with molecular finite automata

The authors propose a theoretical formalism, molecular finite automata (MFA), to describe individual proteins as rule-based computing machines. The MFA formalism provides a framework for modelling individual protein behaviours and systems-level dynamics via construction of programmable and executable machines. Models specified within this formalism explicitly represent the context-sensitive dynamics of individual proteins driven by external inputs and represent protein-protein interactions as synchronised machine reconfigurations. Both deterministic and stochastic simulations can be applied to quantitatively compute the dynamics of MFA models. They apply the MFA formalism to model and simulate a simple example of a signal-transduction system that involves an MAP kinase cascade and a scaffold protein.     

Dynamic vaccination games and hybrid dynamical systems

This paper relates variational inequalities and hybrid dynamical systems to describe the evolution of a class of noncooperative games. To describe such evolution, we define a hybrid system based on a continuous dynamics described by a projected system, and on a finite set of exogenous event times. This hybrid system is then used to track evolution strategies. We apply our results to the evolution of population groups?? strategies playing a noncooperative vaccinating game over a finite time interval.     

Numerical analysis of ion-implantation in target with a rectangular groove

Ion dynamics of pulsed plasma sheath during the plasma source ion-implantation (PSII) affects the resultant surface properties and structures. In this work, a two-dimensional fluid model is applied to the problem of computing ion dynamics in the sheath of a target with a rectangular groove. The evolution of sheath edge, x and y components of ion velocity on the target surface are simulated to describe the physics of sheath in PSII.     

Real-time control of the 3-DOF sled dynamics of a -flux Maglev system with a passive sled

The real-time control of the three degrees of freedom (DOF) dynamics of an electrodynamic (EDS) Maglev vehicle is presented. The design is based on a 5-DOF state-space model of the sled dynamics that uses a simple algebraic model to describe the interaction between the -flux coils on the track and the permanent magnets on the sled. A first-order sliding mode controller with integral error term is used to control heave, pitch, and roll in real time from position-attitude information measured with sensors located on the sled. Experimental results show that control of the 3-DOF dynamics of the levitated vehicle in real time can be successfully achieved by the proposed method.     

Self-similarity in piecewise isometric systems

This paper deals with piecewise isometries and their scaling properties. We aim to present a general framework in which piecewise isometric dynamical systems can be fully or partially renormalized. We precisely describe the dynamics on fractal invariant sets by means of a conjugacy with substitution dynamical systems and Bratteli diagrams. We describe their geometrical properties in terms of graph-directed constructions and we compute their Hausdorff dimension. We also present an example of application to a continuous family of piecewise rotations.     

Publication dynamics: Models and indicators

Models and indicators characterizing the dynamics of national publication productivity distributions are presented. The indicator triplet: transience, renewal, and dynamism is used to describe the «physical shape» of a national scientific community.     

Dynamics of a pulsating spray-diffusion flame

A mathematical model of a fluctuating Burke-Schumann spray-diffusion flame is presented. A sectional approach is utilized to describe the spray of droplets. An analytic solution is presented for a periodically alternating supply of liquid/vapor fuel. Calculated data highlight the dynamics of the flame envelope under the fluctuating supply condition, as well as its sensitivity to liquid-fuel volatility and droplet size (expressed through a nondimensional Damkohler number for evaporation). The predicted flame shape dynamics is rather similar, qualitatively, to some experimental evidence in which flame growth and collapse are observed.     

Collective Shape Oscillation and Domain Formation of Two-Component Bose–Einstein Condensates

In this paper, we describe two kinds of characteristic nonlinear dynamics in two-component Bose–Einstein condensates. For two overlapping components, we analyzed the collective modes and a variety of nonlinear mode couplings, which were then confirmed by numerical simulation of the time-dependent Gross–Pitaevskii equations. Next, we consider the nonlinear dynamics of two condensates after abruptly turning on the intercomponent coupling strength. For strong intercomponent interactions the out-of-phase density wave of the condensates became unstable, leading to mugtiple domain formation.     

Hydrodynamic surface fluctuations of polymer films by coherent X-ray scattering

We have applied X-ray photon correlation spectroscopy (XPCS) to measure the surface dynamics of polymer films of thicknesses down to a few times of the polymer radius of gyration. XPCS is currently the only technique to measure selectively dynamics of surface and/or interfacial fluctuations of the films thanks to high brilliance and coherence of the third generation synchrotron source. The results show the behavior of the capillary waves expected in viscous liquid when the film thickness is thicker than four times of the radius of gyration. However, thinner films show a deviation indicating the need to account for viscoelasticity. We present also the theory for surface dynamics of the thermally excited fluctuations on homogenous single-layer film with arbitrary depth is generalized to describe surface and interfacial dynamics of polymeric liquid bilayer films in terms of susceptibilities, power spectra and characteristic relaxation time constants. The effects on surface dynamics originating from viscosity inhomogeneities close to surface region are investigated by the bilayer theory and compared with the surface dynamics from homogeneous single-layer films under non-slip and slip boundary conditions.     

Hybrid molecular-continuum fluid dynamics

We describe recent developments in the hybrid atomistic/continuum modelling of dense fluids. We discuss the general implementation of mass, momentum and energy transfers between a region described by molecular dynamics and a neighbouring domain described by the Navier-Stokes equations for unsteady continuum fluid flow.     

Modeling and Simulation of the Microstructure Evolution of the Gas-atomized Alloy Droplets during Spray Forming

In order to understand the solidification process of an atomized droplet and predict the fraction solidification of droplets with flight distance during spray forming, a numerical model based on thepopulation dynamics approach is developed to describe the microstructure evolution under the common action of the nucleation and growth of grains.The model is coupled with droplets heat transfer controlling equations and solved for Al-4.5 wt pct Cu alloy. It is demonstrated that the numerical results describe the solidification process well.     

Modeling of integral-type Stirling refrigerator using system dynamics approachModélisation d''un réfrigérateur Stirling de type intégré à l''aide d''une approche par dynamique du système

A modeling of the integral-type Stirling refrigerator (ITSR) using a system dynamics approach is developed in the present study. The system dynamics models are derived to describe the input/output relation of each component of an ITSR. Connecting the equivalent circuits of the components together, we obtain a flow network diagram and derive a transfer function to represent system dynamics behavior of an ITSR. The performance analysis of an ITSR is then easily carried out by use of the transfer function with sinusoidal signal assumption. The performance calculation for a test refrigerator has shown that the analysis is accurate. An empirical correlation for a correction coefficient r in the expansion space was also derived for better results. The present study has demonstrated how a linear system theory or system dynamics approach can be applied to the design of an ITSR.     

Hybrid molecular-continuum fluid models: implementation within a general coupling framework

Over the past three years we have been developing a new approach for the modelling and simulation of complex fluids. This approach is based on a multiscale hybrid scheme, in which two or more contiguous subdomains are dynamically coupled together. One subdomain is described by molecular dynamics while the other is described by continuum fluid dynamics; such coupled models are of considerable importance for the study of fluid dynamics problems in which only a restricted aspect requires a fully molecular representation. Our model is representative of the generic set of coupled models whose algorithmic structure presents interesting opportunities for deployment on a range of architectures including computational grids. Here we describe the implementation of our HybridMD code within a coupling framework that facilitates flexible deployment on such architectures.     

Self-organization and complexity: a new age for theory,computation and experiment

I first describe the notion of self-organization as a property of far-from-equilibrium nonlinear dissipative dynamical systems. Rather than describing such complex systems at a purely phenomenological level, however, I focus attention on the emergent nature of this complexity, by analysing a few examples of physical and physicochemical systems with simple underlying microscopic dynamics yet complex, self-organizing macroscopic properties. These include several mesoscopic models of fluid dynamics as well as a modern approach to nucleation and growth phenomena. Finally, I discuss how the advent of computational grids is set to provide a major boost to the study of such complex, self-organizing systems.     

Challenges in forming inferences from limited data: a case study of malaria parasite maturation

Inferring biological processes from population dynamics is a common challenge in ecology, particularly when faced with incomplete data. This challenge extends to inferring parasite traits from within-host infection dynamics. We focus on rodent malaria infections (Plasmodium berghei), a system for which previous work inferred an immune-mediated extension in the length of the parasite development cycle within red blood cells. By developing a system of delay-differential equations to describe within-host infection dynamics and simulating data, we demonstrate the potential to obtain biased estimates of parasite (and host) traits when key biological processes are not considered. Despite generating infection dynamics using a fixed parasite developmental cycle length, we find that known sources of measurement bias in parasite stage and abundance data can affect estimates of parasite developmental duration, with stage misclassification driving inferences about extended cycle length. We discuss alternative protocols and statistical methods that can mitigate such misestimation.