We propose a systemof partial differential equations with a single constant delay τ > 0 describing the behavior of a one-dimensional thermoelastic solid occupying a bounded interval of R. For an initial-boundary value problem associated with this system, we prove a well-posedness result in a certain topology under appropriate regularity conditions on the data. Further, we show the solution of o...

The system is called a Benjamin-Ono-Boussinesq system because it can be reduced to a pair of equations whose linearization uncouples to a pair of linear Benjamin-Ono equations. Equations of type (1.1) are a class of essential model equations appearing in physics and fluid mechanics. To describe two-dimensional irrotational flows of an inviscid liquid in a uniform rectangular channel, Boussinesq...

We study the initial value problem for the quasi-geostrophic type equations ∂θ ∂t + u · ∇θ + (−∆)θ = 0, on R × (0,∞), θ(x, 0) = θ0(x), x ∈ R n , where λ(0 ≤ λ ≤ 1) is a fixed parameter and u = (uj) is divergence free and determined from θ through the Riesz transform uj = ±Rπ(j)θ, with π(j) a permutation of 1, 2, · · · , n. The initial data θ0 is taken in the Sobolev space L̇r,p with negative ind...

In this paper we prove that for each k, the expressive power of k–ary fixed–point logic, i.e. the fragment of fixed–point logic whose fixed–point operators are restricted to arity ≤ k, strictly exceeds the power of (k − 1)–ary fixed–point logic. This solves a problem that was posed by Chandra and Harel in 1982. Our proof has a rather general form that applies to several variants of fixed–point ...