A variational approach for a generalized emden-fowler equation

Existence of positive solutions of singular boundary value problems related to Emden-Fowler equation is proved. A general minimization theorem in Sobolev spaces is applied.     

A variational approach to the Steiner network problem

Supposen points are given in the plane. Their coordinates form a 2n-vectorX. To study the question of finding the shortest Steiner networkS connecting these points, we allowX to vary over a configuration space. In particular, the Steiner ratio conjecture is well suited to this approach and short proofs of the casesn=4, 5 are discussed. The variational approach was used by us to solve other cases of the ratio conjecture (n=6, see [11] and for arbitraryn points lying on a circle). Recently, Du and Hwang have given a beautiful complete solution of the ratio conjecture, also using a configuration space approach but with convexity as the major idea. We have also solved Graham's problem to decide when the Steiner network is the same as the minimal spanning tree, for points on a circle and on any convex polygon, again using the variational method.     

Dirichlet problem for a nonlocal wave equation

We study the Dirichlet problem for a nonlocal wave equation in a rectangular domain. We prove the existence and uniqueness of a solution of the problem and show that determining whether the solution is unique can be reduced to determining whether a function of Mittag-Leffler type has real zeros. The obtained uniqueness condition turns into the uniqueness condition for the solution of the Dirichlet problem for the wave equation as the order of the fractional derivative in the equation tends to 2.     

A mixed Dirichlet-Robin problem for a nonlinear Kirchhoff-Carrier wave equation

In this paper, a mixed Dirichlet-Robin problem for a nonlinear Kirchhoff-Carrier wave equation is studied. Using the Faedo-Galerkin method and the linearization method for nonlinear terms, we prove the existence and uniqueness of a weak solution of the above problem. An asymptotic expansion of high order in many small parameters of solutions is also discussed.     

A simple approach to the wave uniqueness problem

We propose a new approach for proving uniqueness of semi-wavefronts in generally non-monotone monostable reaction–diffusion equations with distributed delay. This allows to solve an open problem concerning the uniqueness of non-monotone (hence, slowly oscillating) semi-wavefronts to the KPP–Fisher equation with delay. Similarly, a broad family of the Mackey–Glass type diffusive equations is shown to possess a unique (up to translation) semi-wavefront for each admissible speed.     

A uniqueness theorem for solutions to an inverse problem for the wave equation

It is shown that in a certain wave equation the coefficient is uniquely determined if the Cauchy data are given and if the solution of the equation is known as a function on a plane and of time.Translated from Matematicheskie Zametki, Vol. 19, No. 2, pp. 211–214, February, 1976.The author would like to thank V. G. Romanov for helpful remarks.     

A novel variational approach to pulsating solitons in the cubic-quintic Ginzburg-Landau equation

Comprehensive numerical simulations of pulse solutions of the cubic-quintic Ginzburg-Landau equation (CGLE) reveal various intriguing and entirely novel classes of solutions. In particular, there are five new classes of pulse or solitary wave solutions, i.e., pulsating, creeping, snake, erupting, and chaotic solitons that are not stationary in time. They are spatially confined pulse-type structures whose envelopes exhibit complicated temporal dynamics. The numerical simulations also reveal very interesting bifurcation sequences of these pulses as the CGLE parameters are varied. We address the issues of central interest in this area, i.e., the conditions for the occurrence of the five categories of dissipative solitons and also the dependence of both their shape and their stability on the various CGLE parameters, i.e., the nonlinearity, dispersion, linear and nonlinear gain, loss, and spectral filtering. Our predictions for the variation of the soliton amplitudes, widths, and periods with the CGLE parameters agree with the simulation results. We here present detailed results for the pulsating solitary waves. Their regimes of occurrence, bifurcations, and the parameter dependences of the amplitudes, widths, and periods agree with the simulation results. We will address snakes and chaotic solitons in subsequent papers. This overall approach fails to address only the dissipative solitons in one class, i.e., the exploding or erupting solitons. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 152, No. 2, pp. 339–355, August, 2007.     

On the existence and uniqueness of solutions to an asymptotic equation of a variational wave equation

We prove the global existence and uniqueness of admissible weak solutions to an asymptotic equation of a nonlinear hyperbolic variational wave equation with nonnegative L ²(ℝ) initial data. The work of Ping Zhang is supported by the Chinese postdoctor’s foundation, and that of Yuxi Zheng is supported in part by NSF DMS-9703711 and the Alfred P. Sloan Research Fellows award.     

A HJB-POD feedback synthesis approach for the wave equation

We propose a computational approach for the solution of an optimal control problem governed by the wave equation. We aim at obtaining approximate feedback laws by means of the application of the dynamic programming principle. Since this methodology is only applicable for low-dimensional dynamical systems, we first introduce a reduced-order model for the wave equation by means of Proper Orthogonal Decomposition. The coupling between the reduced-order model and the related dynamic programming equation allows to obtain the desired approximation of the feedback law. We discuss numerical aspects of the feedback synthesis and providenumerical tests illustrating this approach.     

Behavior of the formal solution to a mixed problem for the wave equation

The behavior of the formal solution, obtained by the Fourier method, to a mixed problem for the wave equation with arbitrary two-point boundary conditions and the initial condition φ(х) (for zero initial velocity) with weaker requirements than those for the classical solution is analyzed. An approach based on the Cauchy–Poincare technique, consisting in the contour integration of the resolvent of the operator generated by the corresponding spectral problem, is used. Conditions giving the solution to the mixed problem when the wave equation is satisfied only almost everywhere are found. When φ(x) is an arbitrary function from L₂[0, 1], the formal solution converges almost everywhere and is a generalized solution to the mixed problem.     

The Dirichlet problem for the wave equation

Summary We consider a vibrating string fixed at the ends for which the position is known at two different times. This corrisponds to a classical not well posed problem, theDirichlet problem for the wave equation, which we reconsider here in order to determine under what conditions it is possible to obtain useful information about the physical phenomenon. This problem is related to a functional equation from which the principal results can be deduced.

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Sunto Si riesamina un classico esempio di problema ? non ben posto ?, il problema diDirichlet corrispondente al modello fisico di una corda vibrante, fissa agli estremi e assumente posizioni note in due diversi istanti. Lo studio relativo all'esistenza ed unicità della soluzione è ricondotto a quello di una equazione funzionale ed è strettamente connesso a questioni di teoria dei numeri. Si esamina poi la dipendenza della soluzione dai dati e si discute il problema dal punto di vista delle sue applicazioni.

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This research was supported in part by the United States Air Force under contract No. AF 49 (638) 228 monitored by the Office of Scientific Research, Air Research and Development Command.     

A minimum effort optimal control problem for the wave equation

A minimum effort optimal control problem for the undamped wave equation is considered which involves L ^∞-control costs. Since the problem is non-differentiable a regularized problem is introduced. Uniqueness of the solution of the regularized problem is proven and the convergence of the regularized solutions is analyzed. Further, a semi-smooth Newton method is formulated to solve the regularized problems and its superlinear convergence is shown. Thereby special attention has to be paid to the well-posedness of the Newton iteration. Numerical examples confirm the theoretical results.     

A nonlinear approach to absorbing boundary conditions for the semilinear wave equation

We construct a family of absorbing boundary conditions for the semilinear wave equation. Our principal tool is the paradifferential calculus which enables us to deal with nonlinear terms. We show that the corresponding initial boundary value problems are well posed. We finally present numerical experiments illustrating the efficiency of the method.