Homoclinic snaking in bounded domains

Homoclinic snaking is a term used to describe the back and forth oscillation of a branch of time-independent spatially localized states in a bistable, spatially reversible system as the localized structure grows in length by repeatedly adding rolls on either side. On the real line this process continues forever. In finite domains snaking terminates once the domain is filled but the details of how this occurs depend critically on the choice of boundary conditions. With periodic boundary conditions the snaking branches terminate on a branch of spatially periodic states. However, with non-Neumann boundary conditions they turn continuously into a large amplitude filling state that replaces the periodic state. This behavior, shown here in detail for the Swift-Hohenberg equation, explains the phenomenon of “snaking without bistability”, recently observed in simulations of binary fluid convection by Mercader, Batiste, Alonso and Knobloch (preprint)

Computational homogenization of higher-order electro-mechanical materials with built-in generalized periodicity conditions

We present a formulation for high-order generalized periodicity conditions in the context of a high-order electromechanical theory including flexoelectricity, strain gradient elasticity and gradient dielectricity, with the goal of studying periodic architected metamaterials. Such theory results in fourth-order governing partial differential equations, and the periodicity conditions involve continuity across the periodic boundary of primal fields (displacement and electric potential) and their normal derivatives, continuity of the corresponding dual generalized forces (tractions, double tractions, surface charge density and double surface charge density). Rather than imposing these conditions numerically as explicit constraints, we develop an approximation space which fulfils generalized periodicity by construction. Our method naturally allows us to impose general macroscopic fields (strains/stresses and electric fields/electric displacements) along arbitrary directions, enabling the characterization of the material anisotropy. We apply the proposed method to study periodic architected metamaterials with apparent piezoelectricity. We first verify the method by directly comparing the results with a large periodic structure, then apply it to evaluate the anisotropic apparently piezoelectricity of a geometrically polarized 2D lattice, and finally demonstrate the application of the method in a 3D architected metamaterial

A Liquid Model Analogue for Black Hole Thermodynamics

We are able to characterize a 2--dimensional classical fluid sharing some of the same thermodynamic state functions as the Schwarzschild black hole. This phenomenological correspondence between black holes and fluids is established by means of the model liquid's pair-correlation function and the two-body atomic interaction potential. These latter two functions are calculated exactly in terms of the black hole internal (quasilocal) energy and the isothermal compressibility. We find the existence of a ``screening" like effect for the components of the liquid.Comment: 20 pages and 6 Encapsulated PostScript figure

NH3 oxidation and NO reduction by NH3 in N2/Ar and CO2 atmospheres

Impact of using CO2 or N2/Ar as bath gas, representative respectively of oxy-fuel or air combustion scenarios, has been evaluated on the oxidation of ammonia under a variety of operating conditions in a combined experimental and simulation study. Variables of relevance as temperature and oxygen stoichiometry have been considered at atmospheric pressure and under carefully controlled experimental conditions. Additionally, the impact of the presence of NO, which can be formed from ammonia oxidation, has also been evaluated. The experimental results obtained have been simulated with significant success with a detailed literature kinetic mechanism, which has been further used to interpret the main experimental observations. The results obtained are of interest in the power and energy industry, and can be used for guiding the co-firing of NH3 and carbon containing fuels

Conversion of NH3 and NH3-NO mixtures in a CO2 atmosphere. A parametric study

The present work addresses the oxidation of ammonia and ammonia-nitric oxide mixtures in a CO2 atmosphere, characteristic of oxy-fuel processes and/or biogas combustion, from both experimental and kinetic modelling points of view. A parametric study of NH3 and NH3/NO mixtures oxidation is carried out, evaluating the influence of the temperature (700–1500 K), stoichiometry (from pyrolysis, λ = 0, to significantly oxidizing conditions, λ = 3.3), gas residence time (low values, 195/T(K) s and high values, 3100/T(K) s) and NH3/NO ratio (0.5–2.2), at atmospheric pressure under well-controlled laboratory conditions using two tubular flow reactor setups. Experimental results have been simulated with an updated literature reaction mechanism, which has been used to interpret the experimental observations