A New Proof for the Existence of an Equivariant Entire Solution Connecting the Minima of the Potential for the System Δu − W u (u) = 0

Recently, Giorgio Fusco and the author in [2 Alikakos , N.D. , Fusco , G. ( 2011 ). Entire solutions to equivariant elliptic systems with variational structure . Arch. Rat. Mech. Anal. 202 : 567 – 597 .[Crossref], [Web of Science ®] , [Google Scholar]] studied the system Δu ? W _u (u) = 0 for a class of potentials that possess several global minima and are invariant under a general finite reflection group, and established existence of equivariant solutions connecting the minima in certain directions at infinity, together with an estimate. In this paper a new proof is given which, in particular, avoids both the introduction of a pointwise constraint in the minimization process and the equivariant extensions of the various test functions.     

On radially symmetric solutions of the equation ?Δu + u = |u| p-1 u. An ODE approach

Questions of the existence in a ball of radially symmetric solutions of the equation indicated in the title with the Dirichlet zero boundary conditions are studied in many publications and generally speaking, there was obtained more or less complete answer on these questions. It is known now that if the dimension of the space d????3 and 1 <?p?<?(d?+ 2)/(d ? 2) or if d?=?2 and p?>?1, then for any integer l??? 0 this problem in a ball or in the entire space ${x \in \mathbb {R}^d}$ has a radially symmetric solution with precisely l zeros as a function of r?=?|x|. If d??? 3 and p????(d?+?2)/(d ? 2), then the problem in the entire space has no nontrivial solution. For the first time, this problem was studied by a variant of the variational method. However, it is known to the specialists in the field that it is also interesting to obtain the same results by using methods of the qualitative theory of ODEs. In the present article, we shall give a simple proof of the result above in this way. An earlier proof of this result of the other authors is essentially more complicated than our one.     

Hölder Estimates of Solutions on the Equation u t = Δ G ( u )

In this paper we are concerned with the Hölder estimates of solutions of the Cauchy problem for the degenerate parabolic Eq. (1) with the initial data (2), where the diffusion function G ( u ) can be a constant on a non-zero measure set, such as the equations of two-phase Stefan's type. Under the condition | GG "/ G ' 2 | h g , g 2 h 1/2 N , the global estimates | o ( G f ( u ))| h M , on R N ‐ R + , is obtained by using the maximum principle, where f is a constant given in (9).     

A note on the problem −Δu=λu+u|u|2*−2

The dual approach to the problem –u=u+u|u|^2*–2, uþe ₀ ¹ (gW), permits a simple proof of a recent existence result [5] and allows extensions of this result to similar problems also with asymmetric mnonlinearities.Supported by min P.I., Gruppo Naz. (40%) Calcolo delle Variazioni...     

A modification of Newton's method to solve the Dirichlet problem for the equation Δu=f(x,u)

The Dirichlet problem for a weakly nonlinear equation u=f(x, u) is investigated. We use successive approximations constructed by modified Newton's scheme and apply the extremal properties of the solutions of the elliptic equation of the form u – c(x)u=F(x), where c(x) 0. Numerical solution of the resulting sequence of linear boundary-value problems is considered.Translated from Vychislitel'naya i Prikladnaya Matematika, No. 61, pp. 27–30, 1987.     

Liouville-type results for solutions of −Δu=|u|p−1u on unbounded domains of RN

In this Note we study solutions, possibly unbounded and sign-changing, of the equation $?\mathrm{\Delta }u={|u|}^{p?1}u$ on unbounded domains of ${\mathbb{R}}^N$ with $N?2$ and $p>1$. We prove some Liouville-type results and a classification theorem for $C^2$ solutions belonging to one of the following classes: stable solutions, finite Morse index solutions and solutions which are stable outside a compact set. We also extend, to smooth coercive epigraphs, the well-known results of Gidas and Spruck concerning non-negative solutions of the considered equation. To cite this article: A. Farina, C. R. Acad. Sci. Paris, Ser. I 341 (2005).     

Interior and boundary continuity of the solution of the singular equation (β(u))t=Lu

We extend some results of DiBenedetto and Vespri (Arch. Rational Mech. Anal 132(3) (1995) 247) proving the interior and boundary continuity of bounded solutions of the singular equation $\text{(β(u))}{}_{\mathrm{t}}\text{=}\text{L}\text{u}$ where $\text{L}$ is a second order elliptic operator with bounded measurable coefficients that depend both on space and time in a proper way.     

The behavior of bounded solutions to the equation Δu−c(x)u=0 on riemannian manifolds of special type

In the paper we consider solutions of the equation Δu−c(x)u=0,c(x)≥0, on complete Riemannian manifolds constituted as follows: the exterior of some compact set is isometric to the direct product of the semiaxis by some compact manifold with the metricds ²=h ²(r)dr ²+g ²(r)dθ². Necessary and sufficient conditions under which bounded solutions of the equation have a limit independent of θ asr→∞ are obtained and also conditions under which the two-sided Liouville theorem is valid. Translated fromMatematicheskie Zametki, Vol. 65, No. 2, pp. 215–221, February, 1999.     

An Existence Result of the Elliptic Equation Δu+K(x)e~(2u)=0

This paper considers the existence problem of an elliptic equation, which is equivalent to solving the so called prescribing conformal Gaussian curvature problem on the hyperbolic disc H2. An existence result is proved. In particular, K(x) is allowed to be unbounded above.     

New Criterion for the Analyticity of Functions: Representation Via the Metric Tensors of the Surfaces Z = u and Z = ��

Ukrainian Mathematical Journal - We establish a new criterion for the analyticity of a function $$ w=u+i\upupsilon \kern0.5em \mathrm{or}\kern0.5em \overline{w}=u-i\upupsilon, $$ where u(x, y),...     

σ-Moderate solutions of Lu = uα and fine trace on the boundary

We investigate the class of all positive solutions of the equation Lu = u^α, 1 < α ≤ 2, in a smooth domain E ⊂ℝ^d. We define the fine trace tr(u) of a solution u as a pair (Γ, v), where Γ is a set of singular boundary points of u, and v is a certain σ-finite measure on the complement of Γ. We describe all possible traces and we construct the minimal solution with the given trace.     

A mixed formulation of the Stokes equation in terms of (ω,p,u)

The aim of this paper is to give a mixed formulation of the Stokes problem of fluid mechanics in terms of the vorticity, the pressure and the velocity that does not need an artificial boundary condition for vorticity but only the usual compatibility conditions between the pressure space and the velocity space. This revised version was published online in June 2006 with corrections to the Cover Date.     

Smoothness and asymptotics of global positive branches of Δu+λf(u)=0

The smallest eigenvalue of v+ f(0)v=0 gives rise to a global positive branch of u+ f(u)=0 in ² together with homogeneous Dirichlet boundary conditions (f(0)=0,f(0)0). The theory, however, guarantees only that this branch is a continuum. We present a result that in a reasonably large class of problems this branch is actually an unbounded smooth curve. In the second part we study the asymptotic behavior of this positive smooth curve whenf has exponential growth. All results apply also to branches emanating at higher eigenvalues. As shown in [7] they have a fixed nodal structure when restricted to appropriate fixed-point spaces.Dedicated to Prof. Klaus Kirchgässner on the occasion of his sixtieth birthday     

Stability of Runge–Kutta methods in the numerical solution of equation u′(t)=au(t)+a0u([t])

This paper is concerned with the stability analysis of the Runge–Kutta methods for the equation u′(t)=au(t)+a₀u([t]). The stability regions for the Runge–Kutta methods are determined. The conditions that the analytic stability region is contained in the numerical stability region are obtained and some numerical experiments are given.