Showing papers on "Uniform boundedness published in 2011"

Reconstruction from anisotropic random measurements

Abstract: Random matrices are widely used in sparse recovery problems, and the relevant properties of matrices with i.i.d. entries are well understood. The current paper discusses the recently introduced Restricted Eigenvalue (RE) condition, which is among the most general assumptions on the matrix, guaranteeing recovery. We prove a reduction principle showing that the RE condition can be guaranteed by checking the restricted isometry on a certain family of low-dimensional subspaces. This principle allows us to establish the RE condition for several broad classes of random matrices with dependent entries, including random matrices with subgaussian rows and non-trivial covariance structure, as well as matrices with independent rows, and uniformly bounded entries.

Robust Partial-State Feedback Prescribed Performance Control of Cascade Systems With Unknown Nonlinearities

Abstract: A universal controller is designed for cascade systems, involving dynamic uncertainty, unknown nonlinearities, exogenous disturbances and/or time-varying parameters, capable of guaranteeing prescribed performance for the output tracking error, as well as uniformly bounded signals in the closed loop. By prescribed performance we mean that the output tracking error should converge to a predefined arbitrarily small residual set, with convergence rate no less than a certain prespecified value, exhibiting maximum overshoot less than a sufficiently small preassigned constant. The proposed control scheme is of low complexity, utilizes partial state feedback and requires reduced levels of a priori system knowledge. The results can be easily extended to systems affected by bounded state measurement errors, as well as to MIMO nonlinear systems in block triangular form. Simulations clarify and verify the approach.

A proof of the uniform boundedness of solutions to the wave equation on slowly rotating Kerr backgrounds

Abstract: We consider Kerr spacetimes with parameters a and M such that |a|≪M, Kerr-Newman spacetimes with parameters |Q|≪M, |a|≪M, and more generally, stationary axisymmetric black hole exterior spacetimes $(\mathcal{M},g)$ which are sufficiently close to a Schwarzschild metric with parameter M>0 and whose Killing fields span the null generator of the event horizon. We show uniform boundedness on the exterior for solutions to the wave equation □ g ψ=0. The most fundamental statement is at the level of energy: We show that given a suitable foliation Σ τ , then there exists a constant C depending only on the parameter M and the choice of the foliation such that for all solutions ψ, a suitable energy flux through Σ τ is bounded by C times the initial energy flux through Σ0. This energy flux is positive definite and does not degenerate at the horizon, i.e. it agrees with the energy as measured by a local observer. It is shown that a similar boundedness statement holds for all higher order energies, again without degeneration at the horizon. This leads in particular to the pointwise uniform boundedness of ψ, in terms of a higher order initial energy on Σ0. Note that in view of the very general assumptions, the separability properties of the wave equation or geodesic flow on the Kerr background are not used. In fact, the physical mechanism for boundedness uncovered in this paper is independent of the dispersive properties of waves in the high-frequency geometric optics regime.

Fault Tolerant Control for a Class of Nonlinear Systems with Application to Near Space Vehicle

Abstract: In this paper, a fault tolerant control (FTC) scheme, which is based on backstepping and neural network (NN) methodology, is proposed for a general class of nonlinear systems with known structure and unknown faults. Firstly, the linearly parameterized radial basis function (RBF) NNs are employed to approximate unknown system faults, and the network weights are adapted using adaptive on-line parameter-learning algorithms. Then an adaptive backstepping based FTC is designed to compensate for the effect of system faults. The asymptotical stability of the closed-loop system and uniform boundedness of the state tracking errors are proved according to Lyapunov theory. Finally, the designed strategy is applied to near space vehicle (NSV) attitude dynamics, and simulation results are presented to demonstrate the effectiveness of the proposed approach.

On Finite Rank Deformations of Wigner Matrices

Abstract: We study the distribution of the outliers in the spectrum of finite rank deformations of Wigner random matrice under the assumption that the off-diagonal matrix entries have uniformly bounded fifth moment and the diagonal entries have uniformly bounded third moment. Using our recent results on the fluctuation of resolvent entries [31],[28], and ideas from [9], we extend results by M.Capitaine, C.Donati-Martin, and D.F\'eral [12], [13].

A local maximal inequality under uniform entropy

Abstract: We derive an upper bound for the mean of the supremum of the empirical process indexed by a class of functions that are known to have variance bounded by a small constant δ. The bound is expressed in the uniform entropy integral of the class at δ. The bound yields a rate of convergence of minimum contrast estimators when applied to the modulus of continuity of the contrast functions.

Existence of minimizers for spectral problems

Abstract: In this paper we show that any increasing functional of the first k eigenvalues of the Dirichlet Laplacian admits a (quasi-)open minimizer among the subsets of R^N of unit measure. In particular, there exists such a minimizer which is bounded, where the bound depends on k and N, but not on the functional. In the meantime, we show that the ratio \lambda_k(\Omega)/\lambda_1(\Omega) is uniformly bounded for sets \Omega\in R^N.

Competitive Lotka-Volterra Population Dynamics with Jumps

Abstract: This paper considers competitive Lotka-Volterra population dynamics with jumps. The contributions of this paper are as follows. (a) We show stochastic differential equation (SDE) with jumps associated with the model has a unique global positive solution; (b) We discuss the uniform boundedness of $p$th moment with $p>0$ and reveal the sample Lyapunov exponents; (c) Using a variation-of-constants formula for a class of SDEs with jumps, we provide explicit solution for 1-dimensional competitive Lotka-Volterra population dynamics with jumps, and investigate the sample Lyapunov exponent for each component and the extinction of our $n$-dimensional model.

Erratum for Boundedness of families of canonically polarized manifolds: A higher dimensional analogue of Shafarevich's conjecture

Abstract: We show that the number of deformation types of canonically polarized manifolds over an arbitrary variety with proper singular locus is nite, and that this number is uniformly bounded in any nite type family of base varieties. As a corollary we show that a direct generalization of the geometric version of Shafarevich’s original conjecture holds for innitesimally rigid families of canonically polarized varieties.

Discrete Gradient Approach to Stochastic Differential Equations with a Conserved Quantity

Abstract: General autonomous stochastic differential equations (SDEs) driven by one-dimensional Brownian motion in the Stratonovich sense with a conserved quantity $I(y)$ are considered. Relying on this conserved quantity, an equivalent “skew gradient” (SG) form of original SDEs is constructed. With the aim of constructing conserved numerical methods, direct discrete gradient approaches which approximate directly the SG system lead to two conserved methods. In indirect discrete gradient approaches, we first split the SG system into subsystems which preserve the original conserved quantity, then apply direct discrete gradient approaches to subsystems to produce two composition schemes. The mean-square convergence of order 1 for these four methods depends on the assumptions that the coefficients of SDEs are Lipschitz continuous with bounded second moments along the solution of SDEs, are twice continuous differentiable, and have derivatives that are uniformly bounded. Three numerical experiments are presented to verify our theoretical analysis and show the advantages of these methods.

On event triggered trajectory tracking for control affine nonlinear systems

Abstract: In this paper we study an event based control algorithm for trajectory tracking in control affine nonlinear systems. The desired trajectory is modelled as the solution of a reference system with an exogenous input. It is assumed that the desired trajectory and the exogenous input to the reference system are uniformly bounded. Given a continuous-time controller that guarantees global uniform asymptotic tracking of the desired trajectory our algorithm provides an event based controller that not only guarantees semiglobal uniform ultimate boundedness of the tracking error, but also ensures non-accumulation of inter-execution times. In the special case that the derivative of the exogenous input to the reference system is also uniformly bounded, the proposed control algorithm can be used to design an ultimate bound that is arbitrarily small. The main ideas in the paper are illustrated through simulations of trajectory tracking by a nonlinear system.

Absence of line fields and Mañé’s theorem for nonrecurrent transcendental functions

Abstract: Let f : C -> (C) over cap be a transcendental meromorphic function. Suppose that the finite part P(f)boolean AND C of the postsingular set of f is bounded, that f has no recurrent critical points or wandering domains, and that the degree of pre-poles of f is uniformly bounded. Then we show that f supports no invariant line fields on its Julia set. We prove this by generalizing two results about rational functions to the transcendental setting: a theorem of Mane (1993) about the branching of iterated preimages of disks, and a theorem of McMullen (1994) regarding the absence of invariant line fields for "measurably transitive" functions. Both our theorems extend results previously obtained by Graczyk, Kotus and Swiatek (2004).

Identification of continuous-time state-space models from non-uniform fast-sampled data

Abstract: In this study, we apply the expectation-maximisation (EM) algorithm to identify continuous-time state-space models from non-uniformly fast-sampled data. The sampling intervals are assumed to be small and uniformly bounded. The authors use a parameterisation of the sampled-data model in incremental form in order to modify the standard formulation of the EM algorithm for discrete-time models. The parameters of the incremental model converge to the parameter of the continuous-time system description as the sampling period goes to zero. The benefits of the proposed algorithm are successfully demonstrated via simulation studies.

Exponential attractors for non-autonomous dissipative system

Abstract: In this paper we will introduce a version of exponential attractor for non-autonomous equations as a time dependent set with uniformly bounded finite fractal dimension which is positively invariant and attracts every bounded set at an exponential rate. This is a natural generalization of the existent notion for autonomous equations. A generation theorem will be proved under the assumption that the evolution operator is a compact perturbation of a contraction. In the second half of the paper, these results will be applied to some non-autonomous chemotaxis system.

On the Conditions to Extend Ricci Flow

Abstract: Along a Ricci flow solution on a closed manifold, we show that if Ricci curvature is uniformly bounded from below, then a scalar curvature integral bound is enough to extend flow. Moreover, this integral bound condition is optimal in some sense.

On Multi-Dimensional Sonic-Subsonic Flow

Abstract: In this paper, a compensated compactness framework is established for sonic-subsonic approximate solutions to the $n$-dimensional$(n\geq 2)$ Euler equations for steady irrotational flow that may contain stagnation points. This compactness framework holds provided that the approximate solutions are uniformly bounded and satisfy $H^{-1}_{loc}(\Omega)$ compactness conditions. As illustration, we show the existence of sonic-subsonic weak solution to n-dimensional$(n\geq 2)$ Euler equations for steady irrotational flow past obstacles or through an infinitely long nozzle. This is the first result concerning the sonic-subsonic limit for $n$-dimension$(n\geq 3)$.

A Really Simple Elementary Proof of the Uniform Boundedness Theorem

Abstract: I give a proof of the uniform boundedness theorem that is elementary (i.e., does not use any version of the Baire category theorem) and also extremely simple.

An approximation theorem in Musielak-Orlicz-Sobolev spaces

Abstract: In this paper we prove the uniform boundedness of the operators of co- nvolution in the Musielak-Orlicz spaces and the density of C 1 0 (R n ) in the Musielak-

An ultrafilter approach to Jin’s theorem

Abstract: It is well known and not difficult to prove that if C ⊆ ℤ has positive upper Banach density, the set of differences C − C is syndetic, i.e. the length of gaps is uniformly bounded. More surprisingly, Renling Jin showed that whenever A and B have positive upper Banach density, then A − B is piecewise syndetic.

A delay-derivative-dependent approach to robust H∞ filter design for uncertain systems with time-varying distributed delays

Abstract: This paper focuses on the problem of robust H∞ filter design for uncertain systems with time-varying state and distributed delays. System uncertainties are considered as norm-bounded time-varying parametric uncertainties. The delays are assumed to be time-varying delays being differentiable uniformly bounded with delay-derivative bounded by a constant, which may be greater than one. A new delay-derivative-dependent approach of filter design for the systems is proposed. A novel Lyapunov–Krasovskii functional (LKF) is employed, and a tighter upper bound of its derivative is obtained by employing an inequality and using free-weighting matrices technique, then the proposed result has advantages over some existing results, in that it has less conservatism and it enlarges the application scope. An improved sufficient condition for the existence of such a filter is established in terms of linear matrix inequality (LMI). Finally, illustrative examples are given to show the effectiveness and reduced conservatism of the proposed method.

Smallest singular value of sparse random matrices

Abstract: We extend probability estimates on the smallest singular value of random matrices with independent entries to a class of sparse random matrices. We show that one can relax a previously used condition of uniform boundedness of the variances from below. This allows us to consider matrices with null entries or, more generally, with entries having small variances. Our results do not assume identical distribution of the entries of a random matrix and help to clarify the role of the variances of the entries. We also show that it is enough to require boundedness from above of the $r$-th moment, $r > 2$, of the corresponding entries.

Automatic structures of bounded degree revisited

Abstract: The first-order theory of a string automatic structure is known to be decidable, but there are examples of string automatic structures with nonelementary first-order theories. We prove that the first-order theory of a string automatic structure of bounded degree is decidable in doubly exponential space (for injective automatic presentations, this holds even uniformly). This result is shown to be optimal since we also present a string automatic structure of bounded degree whose first-order theory is hard for 2EXPSPACE. We prove similar results also for tree automatic structures. These findings close the gaps left open in a previous paper of the second author by improving both, the lower and the upper bounds.

Uniformly bounded composition operators between general Lipschitz function normed spaces

Abstract: The notions of uniform boundedness and equidistant uniform boundedness of an operator (both weaker then usual boundedness) are introduced. The main results say that the generator of any uniformly bounded (or equidistantly uniformly bounded) composition Nemytskiĭ operator acting between general Lipschitzian normed function spaces must be affine with respect to the function variable.

A Multi-Fluid Compressible System as the Limit of Weak Solutions of the Isentropic Compressible Navier-Stokes Equations

Abstract: This paper mainly concerns the mathematical justification of a viscous compressible multi-fluid model linked to the Baer-Nunziato model used by engineers, see for instance Ishii (Thermo-fluid dynamic theory of two-phase flow, Eyrolles, Paris, 1975), under a “stratification” assumption. More precisely, we show that some approximate finite-energy weak solutions of the isentropic compressible Navier–Stokes equations converge, on a short time interval, to the strong solution of this viscous compressible multi-fluid model, provided the initial density sequence is uniformly bounded with corresponding Young measures which are linear convex combinations of m Dirac measures. To the authors’ knowledge, this provides, in the multidimensional in space case, a first positive answer to an open question, see Hillairet (J Math Fluid Mech 9:343–376, 2007), with a stratification assumption. The proof is based on the weak solutions constructed by Desjardins (Commun Partial Differ Equ 22(5–6):977–1008, 1997) and on the existence and uniqueness of a local strong solution for the multi-fluid model established by Hillairet assuming initial density to be far from vacuum. In a first step, adapting the ideas from Hoff and Santos (Arch Ration Mech Anal 188:509–543, 2008), we prove that the sequence of weak solutions built by Desjardins has extra regularity linked to the divergence of the velocity without any relation assumption between λ and μ. Coupled with the uniform bound of the density property, this allows us to use appropriate defect measures and their nice properties introduced and proved by Hillairet (Aspects interactifs de la m’ecanique des fluides, PhD Thesis, ENS Lyon, 2005) in order to prove that the Young measure associated to the weak limit is the convex combination of m Dirac measures. Finally, under a non-degeneracy assumption of this combination (“stratification” assumption), this provides a multi-fluid system. Using a weak–strong uniqueness argument, we prove that this convex combination is the one corresponding to the strong solution of the multi-fluid model built by Hillairet, if initial data are equal. We will briefly discuss this assumption. To complete the paper, we also present a blow-up criterion for this multi-fluid system following (Huang et al. in Serrin type criterion for the three-dimensional viscous compressible flows, arXiv, 2010).