Group classification,optimal system and optimal reductions of a class of Klein Gordon equations

Complete symmetry analysis is presented for non-linear Klein Gordon equations $u_{\mathit{tt}}=u_{\mathit{xx}}+f(u)$. A group classification is carried out by finding $f(u)$ that give larger symmetry algebra. One-dimensional optimal system is determined for symmetry algebras obtained through group classification. The subalgebras in one-dimensional optimal system and their conjugacy classes in the corresponding normalizers are employed to obtain, up to conjugacy, all reductions of equation by two-dimensional subalgebras. This is a new idea which improves the computational complexity involved in finding all possible reductions of a PDE of the form $F(x\text{,}t\text{,}u\text{,}{u}_x\text{,}{u}_t\text{,}{u}_{\mathit{xx}}\text{,}{u}_{\mathit{tt}}\text{,}{u}_{\mathit{xt}})=0$ to a first order ODE. Some exact solutions are also found.     

The existence of solutions for boundary value problem of fractional hybrid differential equations

In this paper, we study the existence of solutions for the boundary value problem of fractional hybrid differential equations$D_{0^{+}}^{\alpha }\left[\frac{x(t)}{f(t\text{,}x(t))}\right]+g(t\text{,}x(t))=0\text{,}0<t<1\text{,}$$x(0)=x(1)=0\text{,}$where $1<\alpha ?2$ is a real number, $D_{0^{+}}^{\alpha }$ is the Riemann–Liouville fractional derivative. By a fixed point theorem in Banach algebra due to Dhage, an existence theorem for fractional hybrid differential equations is proved under mixed Lipschitz and Carathéodory conditions. As an application, examples are presented to illustrate the main results.     

On the second-order approximate symmetry classification and optimal systems of subalgebras for a forced Korteweg–de Vries equation

We investigate a forced Korteweg–de Vries (fKdV) equation, $u_{\text{,}t}+{\mathit{cu}}_{\text{,}x}+\alpha {\mathit{uu}}_{\text{,}x}+\beta u_{\text{,}\mathit{xxx}}=\beta F(t)$, which arises in the modelling of tsunami generation by submarine landslides. Approximate symmetries are found for the fKdV equation using the method as proposed by Fushchich and Shtelen [6]. Symmetries are found to second order in the perturbation parameter using the MAPLE symmetry package ASP [11], an add-on to the symmetry package DESOLVII [18]. ASP also allows particular forms of the arbitrary function $F(t)$ to be found which extend the symmetry algebra and hence a full approximate symmetry classification of the fKdV equation is obtained. Optimal systems of one-dimensional subalgebras are also determined. Corresponding approximate invariant solutions to the fKdV equation are then constructed for particular $F(t)$ using DESOLVII routines.     

ASYMPTOTIC STABILITY OF RAREFACTION WAVE FOR GENERALIZED BURGERS EQUATION

This paper is concerned with the stability of the rarefaction wave for the Burgers equationwhere 0 ≤ a < 1/4p (q is determined by (2.2)). Roughly speaking, under the assumption that u_ < u , the authors prove the existence of the global smooth solution to the Cauchy problem (I), also find the solution u(x, t) to the Cauchy problem (I) satisfying sup |u(x, t) -uR(x/t)| → 0 as t → ∞, where uR(x/t) is the rarefaction wave of the non-viscous Burgersequation ut f(u)x = 0 with Riemann initial data u(x, 0) =     

Elastic beam problem with higher order derivatives

We apply a fixed point theorem to obtain sufficient conditions for existence of triple positive solutions of the symmetric nonlinear fourth-order boundary value problem$u^{(4)}(t)=a(t)f(t,u(t),|u^{\prime }(t)|,u^{″}(t),|u^{‴}(t)|),t\in (-1,1)\text{,}$$u(-1)=u^{\prime }(-1)=0\text{,}$$u(-t)=u(t),t\in [-1,1]\text{,}$where f satisfies certain growth conditions. In the process, we obtain nontrivial a priori bounds on the derivatives of the solution.     

On the class group and S-class group of formal power series rings

Let ${\text{Cl}}_t(A)$ denote the t-class group of an integral domain A. P. Samuel has established that if A is a Krull domain then the mapping ${\text{Cl}}_t(A)\to {\text{Cl}}_t(A?X?)$, is injective and if A is a regular UFD, then ${\text{Cl}}_t(A)\to {\text{Cl}}_t(A?X?)$, is bijective. Later, L. Claborn extended this result in case A is a regular Noetherian domain. In the first part of this paper we prove that the mapping ${\text{Cl}}_t(A)\to {\text{Cl}}_t(A?X?)$; $[I]?[{(I.A?X?)}_t]$ is an injective homomorphism and in case of an integral domain A such that each υ-invertible υ-ideal of A has υ-finite type, we give an equivalent condition for ${\text{Cl}}_t(A)\to {\text{Cl}}_t(A?X?)$, to be bijective, thus generalizing the result of Claborn. In the second part of this paper, we define the S-class group of an integral domain A: let S be a (not necessarily saturated) multiplicative subset of an integral domain A. Following [11], a nonzero fractional ideal I of A is S-principal if there exist an $s\in S$ and $a\in I$ such that $sI?aA?I$. The S-class group of A, S-${\text{Cl}}_t(A)$ is the group of fractional t-invertible t-ideals of A under t-multiplication modulo its subgroup of S-principal t-invertible t-ideals of A. We generalize some known results developed for the classic contexts of Krull and PυMD domain and we investigate the case of isomorphism S-${\text{Cl}}_t(A)?S$-${\text{Cl}}_t(A?X?)$.     

Exponential stability for the wave model with localized memory in a past history framework

In this paper we discuss the asymptotic stability as well as the well-posedness of the damped wave equation posed on a bounded domain Ω of ${\mathbb{R}}^n,n\ge 2$,

$\rho (x)u_{tt}?\mathrm{\Delta }u+\underset{0}{\overset{\infty }{\int }}g(s)\text{div}[a(x)\mathrm{?}u(?,t?s)]ds+b(x)u_t=0,$

subject to a locally distributed viscoelastic effect driven by a nonnegative function $a(x)$ and supplemented with a frictional damping $b(x)\ge 0$ acting on a region A of Ω, where $a=0$ in A. Assuming that $\rho (x)$ is constant, considering that the well-known geometric control condition $(\omega ,T_0)$ holds and supposing that the relaxation function g is bounded by a function that decays exponentially to zero, we prove that the solutions to the corresponding partial viscoelastic model decay exponentially to zero, even in the absence of the frictional dissipative effect. In addition, in some suitable cases where the material density $\rho (x)$ is not constant, it is also possible to remove the frictional damping term $b(x)u_t$, that is, the localized viscoelastic damping is strong enough to assure that the system is exponentially stable. The semi-linear case is also considered.     

Periodic solutions for a kind of Liénard equation with two deviating arguments

In this paper, we use the coincidence degree theory to establish new results on the existence of T-periodic solutions for the Liénard equation with two deviating arguments of the form$x^{″}(t)+f(x(t))x^{\prime }(t)+g_1(t,x(t-{\tau }_1(t)))+g_2(t,x(t-{\tau }_2(t)))=p(t)\text{.}$