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Larger Class (larger + class)
Selected AbstractsA viscous vortex particle method for deforming bodies with application to biolocomotionINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2009Li Jeany Zhang Abstract Bio-inspired mechanics of locomotion generally consist of the interaction of flexible structures with the surrounding fluid to generate propulsive forces. In this work, we extend, for the first time, the viscous vortex particle method (VVPM) to continuously deforming two-dimensional bodies. The VVPM is a high-fidelity Navier,Stokes computational method that captures the fluid motion through evolution of vorticity-bearing computational particles. The kinematics of the deforming body surface are accounted for via a surface integral in the Biot,Savart velocity. The spurious slip velocity in each time step is removed by computing an equivalent vortex sheet and allowing it to flux to adjacent particles; hence, no-slip boundary conditions are enforced. Particles of both uniform and variable size are utilized, and their relative merits are considered. The placement of this method in the larger class of immersed boundary methods is explored. Validation of the method is carried out on the problem of a periodically deforming circular cylinder immersed in a stagnant fluid, for which an analytical solution exists when the deformations are small. We show that the computed vorticity and velocity of this motion are both in excellent agreement with the analytical solution. Finally, we explore the fluid dynamics of a simple fish-like shape undergoing undulatory motion when immersed in a uniform free stream, to demonstrate the application of the method to investigations of biomorphic locomotion. Copyright © 2008 John Wiley & Sons, Ltd. [source] Some conditions which make the constantly scaled H, control synthesis problems convexINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 1 2002Toru Asai Abstract In this paper, we present some computationally tractable conditions which make the constantly scaled H, control synthesis problem convex. If one of the conditions proposed in this paper holds, the constantly scaled H, control synthesis problem can be solved efficiently as an LMI problem. The results presented here include the existing results such as the state feedback and the full information problems as special cases. In addition, the results are generalized to the case that some of state variables are exactly available. Owing to this generalization, a larger class of problems can be reduced to convex problems, while reduced order controllers can be obtained. Copyright © 2001 John Wiley & Sons, Ltd. [source] Generalization of the Nyquist robust stability margin and its application to systems with real affine parametric uncertaintiesINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 15 2001Charles T. Baab The critical direction theory for analysing the robust stability of uncertain feedback systems is generalized to include the case of non-convex critical value sets, hence making the approach applicable for a much larger class of relevant systems. A redefinition of the critical perturbation radius is introduced, leading to the formulation of a Nyquist robust stability measure that preserves all the properties of the previous theory. The generalized theory is applied to the case of rational systems with an affine uncertainty structure where the uncertain parameters belong to a real rectangular polytope. Necessary and sufficient conditions for robust stability are developed in terms of the feasibility of a tractable linear-equality problem subject to a set of linear inequalities, leading ultimately to a computable Nyquist robust stability margin. A systematic and numerically tractable algorithm is proposed for computing the critical perturbation radius needed for the calculation of the stability margin, and the approach is illustrated via examples. Copyright © 2001 John Wiley & Sons, Ltd. [source] The non-linear dynamics of output and unemployment in the U.S.JOURNAL OF APPLIED ECONOMETRICS, Issue 4 2001Filippo Altissimo This paper studies the joint dynamics of U.S. output and unemployment rate in a non-linear VAR model. The non-linearity is introduced through a feedback variable that endogenously augments the output lags of the VAR in recessionary phases. Sufficient conditions for the ergodicity of the model, potentially applying to a larger class of threshold models, are provided. The linear specification is rejected in favour of our threshold VAR. However, in the estimation the feedback is found to be statistically significant only on unemployment, while it transmits to output through its cross-correlation. This feedback effect from recessions generates important asymmetries in the propagation of shocks, a possible key to interpret the divergence in the measures of persistence in the literature. The regime-dependent persistence also explains the finding that the feedback from recession exerts a positive effect on the long-run growth rate of the economy, an empirical validation of the Schumpeterian macroeconomic theories. Copyright © 2001 John Wiley & Sons, Ltd. [source] Reproductive biology of two co-occurring mugilids, Liza argentea and Myxus elongatus, in south-eastern AustraliaJOURNAL OF FISH BIOLOGY, Issue 4 2008B. W. Kendall The reproductive biology of Liza argentea and Myxus elongatus occurring in two estuaries (Lake Macquarie and St Georges Basin) was found to differ. Gonado-somatic index values and macroscopic staging of gonads identified the peak spawning period of L. argentea occurred between March and November in Lake Macquarie and January and April in St Georges Basin. In contrast, peak spawning of M. elongatus was concentrated between January and March in both estuaries. Spawning of L. argentea probably occurred in the lower reaches of estuaries as well as in nearshore coastal waters, whereas evidence indicated M. elongatus spawned only in ocean waters. The mean fork length at maturity (LF50) was greater for females than males in both species, and it also occurred at a larger mean LF in M. elongatus (males = 230 mm and females = 255 mm) than L. argentea (males = 180 mm and females = 207 mm). Estimates of total potential fecundity were also greater for M. elongatus (425 484,1 157 029) compared to L. argentea (159 933,548 954). Both species had determinate fecundity and displayed a group synchronous pattern of oocyte development, with two distinct size classes of oocytes present in mature ovaries. Liza argentea probably release the larger class of oocytes in one spawning event, but this could not be established for M. elongatus. [source] Robust design of countercurrent adsorption separation processes: 5.AICHE JOURNAL, Issue 7 2000Nonconstant selectivity Operating conditions for the separation of a binary mixture using a nonadsorbable eluent through simulated moving-bed technology were designed. The results obtained using equilibrium theory for adsorption described by Langmuir models lead to the definition of explicit constraints on the operating parameters to operate the unit in the desired regime of separation. A more general approach was able to produce the same result for a larger class of isotherms. The physical and mathematical conditions defining this larger class of isotherms are discussed, as well as the algorithms necessary to calculate the region of complete separation. Applications to the bi-Langmuir isotherm and the ideal adsorbed solution model, which are more flexible than the Langmuir model and can describe systems where selectivity changes with composition, are discussed. A shortcut method to get an explicit, though approximate, solution is proposed and its accuracy is discussed. [source] Asymptotic self-similarity and wavelet estimation for long-range dependent fractional autoregressive integrated moving average time series with stable innovationsJOURNAL OF TIME SERIES ANALYSIS, Issue 2 2005Stilian Stoev Primary 60G18; 60E07; Secondary 62M10; 63G20 Abstract., Methods for parameter estimation in the presence of long-range dependence and heavy tails are scarce. Fractional autoregressive integrated moving average (FARIMA) time series for positive values of the fractional differencing exponent d can be used to model long-range dependence in the case of heavy-tailed distributions. In this paper, we focus on the estimation of the Hurst parameter H = d + 1/, for long-range dependent FARIMA time series with symmetric , -stable (1 < , < 2) innovations. We establish the consistency and the asymptotic normality of two types of wavelet estimators of the parameter H. We do so by exploiting the fact that the integrated series is asymptotically self-similar with parameter H. When the parameter , is known, we also obtain consistent and asymptotically normal estimators for the fractional differencing exponent d = H , 1/,. Our results hold for a larger class of causal linear processes with stable symmetric innovations. As the wavelet-based estimation method used here is semi-parametric, it allows for a more robust treatment of long-range dependent data than parametric methods. [source] Additive preconditioning in matrix computationsPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2007V. Y. Pan We combine our novel SVD-free additive preconditioning with aggregation and other relevant techniques to facilitate the solution of a linear system of equations and other fundamental matrix computations. Our analysis and experiments show the power of our algorithms, guide us in selecting most effective policies of preconditioning and aggregation, and provide some new insights into these and related subjects. Compared to the popular SVD-based multiplicative preconditioners, our additive preconditioners are generated more readily and for a much larger class of matrices. Furthermore, they better preserve matrix structure and sparseness and have a wider range of applications (e.g., they facilitate the solution of a consistent singular linear system of equations and of the eigen-problem). (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Linear lower bounds for ,c(p) for a class of 2D self-destructive percolation modelsRANDOM STRUCTURES AND ALGORITHMS, Issue 4 2009J. van den Berg Abstract The self-destructive percolation model is defined as follows: Consider percolation with parameter p > pc. Remove the infinite occupied cluster. Finally, give each vertex (or, for bond percolation, each edge) that at this stage is vacant, an extra chance , to become occupied. Let ,c(p) be the minimal value of ,, needed to obtain an infinite occupied cluster in the final configuration. This model was introduced by van den Berg and Brouwer. They showed, for the site model on the square lattice (and a few other 2D lattices satisfying a special technical condition) that ,c(p) , . In particular, ,c(p) is at least linear in p , pc. Although the arguments used by van den Berg and Brouwer look very lattice-specific, we show that they can be suitably modified to obtain similar linear lower bounds for ,c(p) (with p near pc) for a much larger class of 2D lattices, including bond percolation on the square and triangular lattices, and site percolation on the star lattice (or matching lattice) of the square lattice. © 2009 Wiley Periodicals, Inc. Random Struct. Alg., 2009 [source] SEMIPARAMETRIC REGRESSION AND GRAPHICAL MODELSAUSTRALIAN & NEW ZEALAND JOURNAL OF STATISTICS, Issue 1 2009M. P. Wand Summary Semiparametric regression models that use spline basis functions with penalization have graphical model representations. This link is more powerful than previously established mixed model representations of semiparametric regression, as a larger class of models can be accommodated. Complications such as missingness and measurement error are more naturally handled within the graphical model architecture. Directed acyclic graphs, also known as Bayesian networks, play a prominent role. Graphical model-based Bayesian ,inference engines', such as bugs and vibes, facilitate fitting and inference. Underlying these are Markov chain Monte Carlo schemes and recent developments in variational approximation theory and methodology. [source] | |||||||||||||