Multi-time-scale dynamics of road–vehicle systems

This paper investigates higher order simulation schemes and associated covariance equations, extended correspondingly. The methods are derived by means of multiply iterated integrals and applied to road–vehicle systems. To avoid numerical instabilities in case of high vehicle speeds, multi-time-scale dynamics are introduced by scaling the time and noise increments according to the main system frequencies. In the stationary case, the covariances are time-invariant so that Euler schemes can be applied with bigger time steps without systematic errors. Note that deterministic methods as the classical Runge–Kutta approach are consistently applicable to the drift term only, but not to the diffusion of stochastic differential equations.     

Sequential dynamics of master–slave systems

Following on previous work, we discuss a scenario in which two neural ensembles have a master–slave arrangement. We will consider a more particular case in which the master system exhibits transient dynamics due to a stable heteroclinic sequence (SHS) and the slave system has attractors in the form of limit cycles. We will give sufficient conditions that guarantee the existence of a SHS in the form of a tube in the full phase space, together with an open stable heteroclinic channel that surrounds it. We present a numerical observation of chaotic-like transient behaviour different from well-known transient chaos.     

On the occurrence of stable heteroclinic channels in Lotka–Volterra models

The Lotka–Volterra (LV) equations can be used to model the behaviour of complex systems in nature. Trajectories in a stable heteroclinic channel (SHC) describe transient dynamics according to the winnerless competition principle in such a system. The existence of an SHC is guaranteed if the parameters of the LV equations satisfy a number of conditions. We study under what conditions a heteroclinic channel arises in a system where the coupling strengths are chosen randomly. These results describe the overall structure of the system dependent on the length of the channel. This relationship gives an estimation for the possible length of sequences of states in systems occurring in nature.     

Quantum dynamics of the phase of a Bose–Einstein condensate

Abstract

In this review we discuss the dynamics of the phase of trapped Bose–Einstein condensates. In particular we consider the phenomena of phase decoherence (termed also as phase collapse, or diffusion), and phase revival in systems of interacting atoms. We analyse the dependence of the collapse and revival times on the trap potential, dimensionality of the gas, atom number fluctuations, and on the coherent dynamics of the condensate. We show that in a class of experimentally relevant systems, the collapse time is relatively short, and in some cases vanishes in the limit of a large number of atoms, implying that the trapped Bose gas cannot sustain a well-defined quantum phase, and that the phase memory is lost on a relatively short time scale. Furthermore, we calculate the relative atom number fluctuations or a model of two interacting condensates, and show that the fluctuations are generically sub-Poissonian.     

Tension–tension fatigue behavior of layer-to-layer 3-D angle-interlock woven composites

The tension–tension fatigue behavior of (the layer-to-layer) three-dimensional angle-interlock woven composite (3DAWC) was investigated using the acoustic emission (AE) technique, examination of damaged regions via light microscopy and micro-CT, and finite element analysis (FEA). AE events occurred during the entire fatigue process, and damage modes were determined based on cumulative fatigue damage of the 3DAWC undergoing tension-tension cyclic loading. FEA was employed to determine stress distribution and specific regions of stress concentrations within the composite structure. Debonding occurred at the warp tow-matrix-weft tow interface where the warp tows exhibited a maximum in amplitude of undulation. In addition, interrupted tests were performed to investigate fatigue damage modes of the 3DAWC at specific points in the fatigue life. Fatigue damage occurred in three distinct stages with characteristic damage modes.     

Application of a co-continuous composite model of effective thermal conductivity to ice–air systems

Effective thermal conductivity measurements were performed for two ice–air systems (ice chips produced by a commercial ice-maker and synthetic snow) using a transient comparative technique. These systems were chosen because the ice fraction could be controlled, thereby de-coupling the problems of ice fraction and thermal conductivity prediction. None of the commonly used simple effective thermal conductivity models (specifically the Series, Parallel, two forms of the Maxwell–Eucken and Effective Medium Theory models) provided adequate prediction accuracy over the full range of ice fractions in the experimental data. The best predictions were provided by a composite model that combined the Effective Medium Theory structure and the recently developed co-continuous structure.     

Dynamics of an elastic multibody chain: Part B—Global dynamics

In this the second paper in a series describing the dynamics of an arbitrary multibody system, the global dynamics of a topological chain of elasticbodies is considered in detail. The direct-path approach is used in the assignment of coordinate systems, interbody position vectors, connection matrices, and in the handling of mass properties, all in conjunction with a Newton-Euler, finite-element formulation. Nonlinear inertial effects, which can be important during rapid manoeuvres, are also identified.

The equations are first collected in a form appropriate to a chain with unconstrained joints—a full six degrees of freedom are permitted at each interbody joint. Constraints are then selectively introduced and the associated constraint forces calculated using the concept of projection matrices. The associated control forces (to carry out robotics tasks, for example) are also calculated. Finally, a compact form of the motion equations is presented for a multibody chain with constrained-controlled interbody joints.     

The mechanical alloying mechanism of various Fe2O3–Al–Fe systems

The mixed powders of in situ Al₂O₃ particles and Fe (Al) solid solution were prepared via self-propagating combustion reaction initiated by mechanical alloying (MA), and the MA mechanism of several Fe₂O₃–Al–Fe systems with different Al₂O₃ mass fractions were studied. The adiabatic temperature (T_ad) of each system was calculated to estimate whether the self-propagating combustion reaction could be initiated in theory. The microstructure of the mixed powders was investigated by SEM, EDS and TEM. The phase analysis was evaluated by XRD, and the Fe lattice parameter was calculated from the XRD patterns. The results showed that with the addition of Fe during the MA process, the activation period was prolonged and the sharp increase of temperature occurred, and when the Al₂O₃ mass fraction was decreased to 10.94%, the self-propagating combustion reaction could not occur in theory and practice. When there was no added Fe, the final product was homogeneous Fe (Al) solid solution.     

Selection of eutectic systems in AI2O3–Y2O3 ceramics

There are two eutectic reactions in the Al₂0₃–rich portion of the AI₂O₃-Y₂O₃ pseudo–binary system; one is the equilibrium A1₂0₃–YAG eutectic reaction at 1826%C, and the other is the metastable A1₂0₃–YAP eutectic reaction at 1702%C. Selection of the A1₂0₃–YAG and the A1₂0₃–YAP eutectics was examined in terms of cooling rate, nucleation temperature and maximum melt temperature. When the melt was cooled from 2100%C at any cooling rate, it always nucleated below the Al₂0₃–YAP eutectic temperature, therefore the Al₂0₃–YAP eutectic was selected. The Al₂0₃–YAG eutectic was selected when the melt was cooled from 1900%C at a cooling rate of less than 1 K s^-1. The selection of the two eutectic systems was determined by the nucleation temperature, although the maximum holding temperature of the melt and the cooling rate significantly affected the nucleation temperature. The structure of the melt, such as coordination of oxygen and chemical order when being heated to 2100%C may affect the nucleation behavior.     

Selection of eutectic systems in Al2O3–Y2O3 ceramics

There are two eutectic reactions in the Al₂O₃-rich portion of the Al₂O₃–Y₂O₃ pseudo-binary system; one is the equilibrium Al₂O₃–YAG eutectic reaction at 1826°C, and the other is the metastable Al₂O₃–YAP eutectic reaction at 1702°C. Selection of the Al₂O₃–YAG and the Al₂O₃–YAP eutectics was examined in terms of cooling rate, nucleation temperature and maximum melt temperature. When the melt was cooled from 2100°C at any cooling rate, it always nucleated below the Al₂O₃–YAP eutectic temperature, therefore the Al₂O₃–YAP eutectic was selected. The Al₂O₃–YAG eutectic was selected when the melt was cooled from 1900°C at a cooling rate of less than 1 K s⁻¹. The selection of the two eutectic systems was determined by the nucleation temperature, although the maximum holding temperature of the melt and the cooling rate significantly affected the nucleation temperature. The structure of the melt, such as coordination of oxygen and chemical order when being heated to 2100°C may affect the nucleation behavior.     

Supramolecular host–guest systems constructed of pyrrole derivatives and 3D-coordination polymers

Pyrrole derivatives have been shown to be completely or partially oxidized within the expandable channels of the 3D-coordination polymers [(R₃Sn)₃Fe(CN)₆] _n and [(R₃Sn)(R₃^′Sn)₂Fe(CN)₆] _n , R and R′ = Me, n-Bu, or Ph, to give novel class of supramolecular host–guest systems. The structures and physical properties of these host–guest systems depend on the reaction time, nature of the host and guest, the space empty within the network of the 3D-coordination polymers. Pyrrole undergoes oxidative polymerization in the channels of the 3D-coordination polymers to form semiconducting diamagnetic supramolecular host–guest systems. Whereas N-methylpyrrole and 2,5-dimethylpyrrole are not polymerized under these experimental conditions, but give paramagnetic charge transfer (CT) supramolecular host–guest systems.     

Adhesion of thermally sprayed hydroxyapatite–bond-coat systems measured by a novel peel test

Ti6Al4V foils, 100 m thick, were coated with thin (10–15 m) bond coats based on titania and zirconia, and subsequently coated with a thick (100–120 m) hydroxyapatite layer, using atmospheric plasma spraying. Peel adhesion tests of the coating systems performed on the foils showed that titania, and mixed titania/non-stabilized zirconia bond coats improved the adhesion of the ceramic layers to the metallic substrate in a statistically significant way, while a partially CaO-stabilized zirconia bond coat led to a decrease of the peel adhesion strength when compared to hydroxyapatite coatings without a bond coat.     

Non-hydrolytic sol–gel route to a family of hybrid mesoporous aluminosilicate ethanol dehydration catalysts

Journal of Materials Science - Hybrid materials are intensely studied for potential applications in heterogeneous catalysis. Organic groups at the catalyst surface can modify not only its...     

Integrated simulation–optimisation of pull control systems

Pull policies are considered to be among the most efficient control strategy. Setting the correct parameters to maximise their efficiency is, however, not a trivial task. Simulation–optimisation techniques have received particular attention as a means to solve this problem. Nevertheless, they require the iterative solution of an optimisation model to generate the parameter values and a discrete event simulator to evaluate the resulting system performance. In the framework of simulation-optimisation, this paper proposes a combined solution of the optimisation and simulation problems for the optimal operation of pull control systems under several control strategies. Numerical experiments were performed to evaluate the performance of the proposed technique.     

Optimality criteria-based topology optimization of a bi-material model for acoustic–structural coupled systems

This article investigates topology optimization of a bi-material model for acoustic–structural coupled systems. The design variables are volume fractions of inclusion material in a bi-material model constructed by the microstructure-based design domain method (MDDM). The design objective is the minimization of sound pressure level (SPL) in an interior acoustic medium. Sensitivities of SPL with respect to topological design variables are derived concretely by the adjoint method. A relaxed form of optimality criteria (OC) is developed for solving the acoustic–structural coupled optimization problem to find the optimum bi-material distribution. Based on OC and the adjoint method, a topology optimization method to deal with large calculations in acoustic–structural coupled problems is proposed. Numerical examples are given to illustrate the applications of topology optimization for a bi-material plate under a low single-frequency excitation and an aerospace structure under a low frequency-band excitation, and to prove the efficiency of the adjoint method and the relaxed form of OC.