Exact steady periodic water waves with vorticity

We consider the classical water wave problem described by the Euler equations with a free surface under the influence of gravity over a flat bottom. We construct two‐dimensional inviscid periodic traveling waves with vorticity. They are symmetric waves whose profiles are monotone between each crest and trough. We use bifurcation and degree theory to construct a global connected set of such solutions. © 2003 Wiley Periodicals, Inc.     

A nonlinear superposition principle and multibump solutions of periodic Schrödinger equations

In an abstract setting we prove a nonlinear superposition principle for zeros of equivariant vector fields that are asymptotically additive in a well-defined sense. This result is used to obtain multibump solutions for two basic types of periodic stationary Schrödinger equations with superlinear nonlinearity. The nonlinear term may be of convolution type. If the superquadratic term in the energy functional is convex, our results also apply in certain cases if 0 is in a gap of the spectrum of the Schrödinger operator.     

Higher order approximate periodic solutions for nonlinear oscillators with the Hamiltonian approach

In this work, the Hamiltonian approach is applied to obtain the natural frequency of the Duffing oscillator, the nonlinear oscillator with discontinuity and the quintic nonlinear oscillator. The Hamiltonian approach is then extended to the second and third orders to find more precise results. The accuracy of the results obtained is examined through time histories and error analyses for different values for the initial conditions. Excellent agreement of the approximate frequencies and the exact solution is demonstrated. It is shown that this method is powerful and accurate for solving nonlinear conservative oscillatory systems.     

Existence of gap solitons in periodic discrete nonlinear Schrödinger equations

In this paper, we discuss how to use the critical point theory to study the existence of gap solitons for periodic discrete nonlinear Schrödinger equations. An open problem proposed by Professor Alexander Pankov is solved.     

Inclusion-exclusion: Exact and approximate

It is often required to find the probability of the union of givenn eventsA ₁ ,...,A _n . The answer is provided, of course, by the inclusion-exclusion formula: Pr(A _i )= _i – _i<j Pr(A _i A _j )±.... Unfortunately, this formula has exponentially many terms, and only rarely does one manage to carry out the exact calculation. From a computational point of view, finding the probability of the union is an intractable, #P-hard problem, even in very restricted cases. This state of affairs makes it reasonable to seek approximate solutions that are computationally feasible. Attempts to find such approximate solutions have a long history starting already with Boole [1]. A recent step in this direction was taken by Linial and Nisan [4] who sought approximations to the probability of the union, given the probabilities of allj-wise intersections of the events forj=1,...k. The developed a method to approximate Pr(A _i ), from the above data with an additive error of exp . In the present article we develop an expression that can be computed in polynomial time, that, given the sums _|S|=j Pr( _iS A _i ) forj=1,...k, approximates Pr(A _i ) with an additive error of exp . This error is optimal, up to the logarithmic factor implicit in the notation.The problem of enumerating satisfying assignments of a boolean formula in DNF formF=v _l ^m C _i is an instance of the general problem that had been extensively studied [7]. HereA _i is the set of assignments that satisfyC _i , and Pr( _iS A _i )=a _S /2ⁿ where _iS C _i is satisfied bya _S assignments. Judging from the general results, it is hard to expect a decent approximation ofF's number of satisfying assignments, without knowledge of the numbersa _S for, say, all cardinalities . Quite surprisingly, already the numbersa _S over |S|log(n+1)uniquely determine the number of satisfying assignments for F.We point out a connection between our work and the edge-reconstruction conjecture. Finally we discuss other special instances of the problem, e.g., computing permanents of 0,1 matrices, evaluating chromatic polynomials of graphs and for families of events whose VC dimension is bounded.Work supported in part by a grant of the Binational Israel-US Science Foundation.Work supported in part by a grant of the Binational Israel-US Science Foundation and by the Israel Science Foundation.     

Bifurcations and highly nonlinear traveling waves in periodic dimer granular chains

In this study, the highly nonlinear waves in periodic dimer granular chains were investigated by the theory of dynamical system and the method of phase diagram analysis. The bifurcations of the different traveling waves in parameter space and those different traveling waves and its phase diagram were given. In addition, the existence of smooth and non‐smooth traveling wave solutions are shown and various sufficient conditions to guarantee the existence of the above solutions were listed. Copyright © 2011 John Wiley & Sons, Ltd.     

Stability of small periodic waves for the nonlinear Schrödinger equation

The nonlinear Schrödinger equation possesses three distinct six-parameter families of complex-valued quasiperiodic traveling waves, one in the defocusing case and two in the focusing case. All these solutions have the property that their modulus is a periodic function of x−ct for some c∈R. In this paper we investigate the stability of the small amplitude traveling waves, both in the defocusing and the focusing case. Our first result shows that these waves are orbitally stable within the class of solutions which have the same period and the same Floquet exponent as the original wave. Next, we consider general bounded perturbations and focus on spectral stability. We show that the small amplitude traveling waves are stable in the defocusing case, but unstable in the focusing case. The instability is of side-band type, and therefore cannot be detected in the periodic set-up used for the analysis of orbital stability.     

Gap solitons in periodic discrete nonlinear Schrödinger equations with saturable nonlinearities

The main result of the paper concerns the existence of nontrivial exponentially decaying solutions to periodic stationary discrete nonlinear Schrödinger equations with saturable nonlinearities, provided that zero belongs to a spectral gap of the linear part. The proof is based on the critical point theory in combination with periodic approximations of solutions. As a preliminary step, we prove also the existence of nontrivial periodic solutions with arbitrarily large periods.     

Generalized cofactors and nonlinear superposition principles

It is known from Lie's works that the only ordinary differential equation of first order in which the knowledge of a certain number of particular solutions allows the construction of a fundamental set of solutions is, excepting changes of variables, the Riccati equation. For planar complex polynomial differential systems, the classical Darboux integrability theory exists based on the fact that a sufficient number of invariant algebraic curves permits the construction of a first integral or an inverse integrating factor. In this paper, we present a generalization of the Darboux integrability theory based on the definition of generalized cofactors.     

Cauchy problem for a model of nonlinear waves generated in viscous films

This work studies a two‐dimensional version of the Korteweg–de Vries equation, which is the so‐called anisotropic dissipation‐modified Boussinesq–Korteweg–de Vries equation. The local well‐posedness for the Cauchy problem associated with this equation is proven when the initial value belongs to the Sobolev space , for all s > ? 1 ∕ 6. A global existence result will be obtained under suitable conditions. Copyright © 2012 John Wiley & Sons, Ltd.     

Almost periodic events generated by random flows

Under suitable conditions, a measurable action of a semigroup S on a probability space $(\varOmega,\mathcal {F},\mu )$ generates various σ-fields reflecting the dynamical properties of the associated representation of S and containing the information provided by certain subspaces of $\mathcal {L}^{1}(\mu )$ determined by the representation. For example, the functions in $\mathcal {L}^{1}(\mu )$ with norm relatively compact orbits under S are precisely the $\mathcal {L}^{1}$ functions that are measurable with respect to the σ-field of almost periodic events. In the special case of a measure-preserving action, the minimal projection operator associated with the action is a conditional expectation with respect to this σ-field, leading to a result on transformation of martingales. The unifying construct throughout the paper is the weakly almost periodic compactification of S, a powerful tool that provides a convenient platform to study operator semigroups associated with the action.     

Exact and approximate solutions to the multisource weber problem

The problem considered is the choice of locations form sources so as to minimize the sum of weighted distances betweenn fixed sinks and the source closest to each sink. The weights represent the amounts to be shipped between the sinks and their respective sources; the allowable source locations are free of restriction. An algorithm for the approximate solution of the problem, and computational experience with it, are discussed first. A branch-and-bound algorithm for exact solution of the problem is then developed, and computational experience with it is described.For a more detailed discussion of the analyses contained in the present paper, the computational results, and for detailed program listings, the reader is referred to [8]. Tapes for the two programs discussed in the present paper are available at cost of reproduction from Program Analysis Division, Institute for Defense Analyses, Arlington, Virginia.     

Exact sequences of algebras generated by singular integral operators

An abstract theorem concerning exact sequences of Banach algebras of operators and symbol homomorphisms relative to groups of operators is derived. This general result is used to deduce many of the classical spectral inclusion theorems and short exact sequences for algebras of singular integral operators.This work partially supported by a grant from the National Science Foundation.     

Exact solitary and periodic wave solutions for a generalized nonlinear Schrödinger equation

The generalized nonlinear Schrödinger equation (GNLS) iu_t + u_xx + βu²u + γu⁴u + iα (u²u)_x + iτ(u²)_xu = 0 is studied. Using the bifurcation of travelling waves of this equation, some exact solitary wave solutions were obtained in [Wang W, Sun J,Chen G, Bifurcation, Exact solutions and nonsmooth behavior of solitary waves in the generalized nonlinear Schrödinger equation. Int J Bifucat Chaos 2005:3295–305.]. In this paper, more explicit exact solitary wave solutions and some new smooth periodic wave solutions are obtained.     

Exact and approximate pulsed beam solutions of Maxwell's equations

An exact solution of Maxwell's equations is constructed which represents a pulse of finite energy propagating along a given axis. To simplify the computation of such a pulse, an approximate solution is constructed as a superposition of solutions of the paraxial equation. This approximation is vectorial in nature and satisfies the divergence-free condition. The difference between the exact and approximate solutions is estimated relative to the total energy transfer of the exact solution.     

Dynamic Hopf bifurcations generated by nonlinear terms

We consider the so-called delayed loss of stability phenomenon for singularly perturbed systems of differential equations in case that the associated autonomous system with a scalar parameter undergoes the Hopf bifurcation at the zero equilibrium point. It is assumed that the linearization of the associated system is independent of the parameter and the next terms in the expansion of the right-hand parts at zero are positive homogeneous of order α>1. Simple formulas are presented to estimate the asymptotic delay for the delayed loss of stability phenomenon. More precisely, we suggest sufficient conditions which ensure that zeros of a simple function ψ defined by the positive homogeneous nonlinear terms are the Hopf bifurcation points of the associated system, the sign of ψ at other points determines stability of the zero equilibrium, and the asymptotic delay equals the distance between the bifurcation point and a zero of some primitive of ψ.