Instability Paths in the Kirchhoff–Plateau Problem

The Kirchhoff–Plateau problem concerns the equilibrium shapes of a system in which a flexible filament in the form of a closed loop is spanned by a soap film, with the filament being modeled as a Kirchhoff rod and the action of the spanning surface being solely due to surface tension. Adopting a variational approach, we define an energy associated with shape deformations of the system and then derive general equilibrium and (linear) stability conditions by considering the first and second variations of the energy functional. We analyze in detail the transition to instability of flat circular configurations, which are ground states for the system in the absence of surface tension, when the latter is progressively increased. Such a theoretical study is particularly useful here, since the many different perturbations that can lead to instability make it challenging to perform an exhaustive experimental investigation. We generalize previous results, since we allow the filament to possess a curved intrinsic shape and also to display anisotropic flexural properties (as happens when the cross section of the filament is noncircular). This is accomplished by using a rod energy which is familiar from the modeling of DNA filaments. We find that the presence of intrinsic curvature is necessary to obtain a first buckling mode which is not purely tangent to the spanning surface. We also elucidate the role of twisting buckling modes, which become relevant in the presence of flexural anisotropy.     

Rayleigh–Taylor instability of superposed barotropic fluids

Effects of compressibility on Rayleigh?CTaylor instability of superposed fluids are considered. The density is allowed to vary with pressure under the barotropy assumption. The small-compressibility limit is considered first in order to facilitate an analytical calculation. For the case with equal speeds of sound in the two superposed fluids, a non-trivial analytical compressibility correction to the Rayleigh?CTaylor growth rate becomes feasible if we perturbatively calculate the compressibility correction to O (g ²/k ² a ⁴). To this order, compressibility effects are found to reduce the growth rate. This trend is validated for arbitrary compressibility cases as well via an exact evaluation of the dispersion relation.     

Asymptotic bubble evolutions of the Rayleigh–Taylor instability

We examine the multiple harmonic model for the single-mode Rayleigh–Taylor instability, and present a new class of the asymptotic solution for the bubble evolution. Previously reported solutions for the bubble curvature and velocity from the model were quantitatively different from other theoretical models and numerical results, for small density jumps. The discrepancy between the theoretical models is resolved by our new approach to the model. Our solution agrees with the Layzer–Goncharov model, and gives the independence of the bubble curvature on the density ratio.     

Instability of Standing Wave for the Klein–Gordon–Hartree Equation

The instability property of the standing wave uω(t, x) = eiωtφ(x) for the Klein–Gordon– Hartree equation     

Nonlinear Transmission Problem for Wave Equation with?Boundary Condition of Memory Type

In this paper we consider a transmission problem with a boundary damping condition of memory type, that is, the wave propagation over bodies consisting of two physically different types of materials. One component is clamped, while the other is in a viscoelastic fluid producing a dissipative mechanism on the boundary. We will study the global existence of solutions for the transmission problem, and moreover we show that if the relaxation function decays exponentially or polynomially, then the solutions for the problem have the same decay rates.     

Duchon–Robert solutions for the Rayleigh–Taylor and Muskat problems

We construct analytic solutions to the Euler equations with an interface between two fluids, extending work of Duchon and Robert. We also show that the estimates of Duchon and Robert yield global analytic solutions to the Muskat problem with small initial data.     

Cauchy–Goursat Problem for One-Dimensional Semilinear Wave Equations

We consider the initial-characteristic problem for nonlinear wave equations with positive power nonlinearity source term. Depending on the power of nonlinearity, we investigate the problem on a global existence and blow-up of solutions of initial-characteristic problem. The question on local solvability of the problem is also considered.     

The Dirichlet Problem for a Class of Nonlinear Elliptic Equations

In this paper, we study the Dirichlet problem for the nonlinear an isotropic elliptic equation where is a bounded domain, m_i(i=1, 2, …, n) are positive integers, and a_(ij)(x)(i,j=1,2,…,n) are measurable functions on Ω. The Dirichlet problem for semilinear elliptic equation, (1) with m_i=1 (i=1,2,…, n), has been studied by several people, see e.g [1] and the bibliography in [1]. The general nonlinear problem(1) seems to be studied very little.     

Boundary Control Problem for a Nonlinear Convection–Diffusion–Reaction Equation

Computational Mathematics and Mathematical Physics - The solvability of boundary-value and extremum problems for a nonlinear convection–diffusion–reaction equation with mixed boundary...     

The Interior Layer Problem for the Strongly Nonlinear Singularly Perturbed System

The nonlinear strongly singularly perturbed systemεyi" = fi(t, y,y'), a < t < b, i = 1, 2, …, n, yi(a,ε)-pily'i(a,ε) = Ai, yi(b,ε) pi2y'i(b,ε) = Biare considered. Under suitable conditions, using the theory of differential inequalities the existence and asymptotic behavior of interior solution for the problems are studied.     

The Collapsing 0–1 Knapsack Problem

The Collapsing 0–1 Knapsack Problem is a type of non-linear knapsack problem in which the knapsack size is a non-increasing function of the number of items included.An algorithm is developed and computational results included.     

Rayleigh–Taylor instability for nonhomogeneous incompressible fluids with Navier-slip boundary conditions

This paper is concerned with the Rayleigh–Taylor instability for the nonhomogeneous incompressible Navier–Stokes equations with Navier-slip boundary conditions around a steady state in an infinite slab, where the Navier-slip coefficients do not have defined sign and the slab is horizontally periodic. Motivated by Jiang et al. (Sci. China Math., 2013), we extend the result from Dirichlet boundary condition to Navier-slip boundary conditions. Our results indicate the factor that “heavier density with increasing height” still plays a key role in the instability under Navier-slip boundary conditions.     

Nonlinear dynamics of laminar-turbulent transition in three dimensional Rayleigh–Benard convection

This paper proposes a new approach to analysis of incompressible 3D fluid motion in Rayleigh–Benard convection in transition from laminar to turbulent regimes. Number of test series were conducted. The analysis indicated that in different test series laminar-turbulent transition follows either the subharmonic bifurcation cascade of two-dimensional tori or the subharmonic bifurcation cascade of limit cycles. Cycles up to the third period were found in the system that indicated the end of the Sharkovskii sequence. All bifurcation cascades agree with the Feigenbaum–Sharkovskii–Magnitskii (FSM) scenario.     

On Instability of the Rayleigh–Bénard Problem without Thermal Diffusion in a Bounded Domain under L1-Norm

We investigate the thermal instability of a three-dimensional Rayleigh–Bénard(RB for short) problem without thermal diffusion in a bounded domain. First we construct unstable solutions in exponential growth modes for the linear RB problem. Then we derive energy estimates for the nonlinear solutions by a method of a prior energy estimates, and establish a Gronwall-type energy inequality for the nonlinear solutions. Finally, we estimate for the error of L¹-norm between the both solution...     

The Cauchy Problem for Nonlinear Parabolic Equations with Lévy Laplacian

A solution to the Cauchy problem for a rather general class of nonlinear parabolic equations involving the infinite-dimensional Laplacian Δ_L of the form , where f is a real function defined on R³ is presented. Mathematics Subject Classifications (2000) 35R15, 46G05.     

Turing Instability and Pattern Formation for the Lengyel–Epstein System with Nonlinear Diffusion

In this work we study the effect of density dependent nonlinear diffusion on pattern formation in the Lengyel–Epstein system. Via the linear stability analysis we determine both the Turing and the Hopf instability boundaries and we show how nonlinear diffusion intensifies the tendency to pattern formation; in particular, unlike the case of classical linear diffusion, the Turing instability can occur even when diffusion of the inhibitor is significantly slower than activator’s one. In the Turing pattern region we perform the WNL multiple scales analysis to derive the equations for the amplitude of the stationary pattern, both in the supercritical and in the subcritical case. Moreover, we compute the complex Ginzburg–Landau equation in the vicinity of the Hopf bifurcation point as it gives a slow spatio-temporal modulation of the phase and amplitude of the homogeneous oscillatory solution.     

The Cauchy Problem of the Nonlinear Schrodinger Equations in R^1＋1

In this paper, we consider the local and global solution for the nonlinear Schrodinger equation with data in the homogeneous and nonhomogeneous Besov space and the scattering result for small data. The techniques to be used are adapted from the Strichartz type estimate, Kato＇s smoothing effect and the maximal function （in time） estimate for the free SchrSdinger operator.