Creep response of sandwich beams with a metallic foam core

The creep response of metallic foam sandwich beams in 3-point bend is investigated numerically for the case of a metallic foam core and two steel faces. The face sheets are treated as elastic, while the foam core is modeled by a viscoplastic extension of the Deshpande-Fleck yield surface. This power-law creeping constitutive law has been implemented within the commercial finite element code ABAQUS. It is found that the beams creep by a variety of competing mechanisms, depending upon the choice of material properties and the geometric parameters. A failure map is constructed and effect of rate dependence on the load-deflection curves is quantified, and compared against the available experimental data.

Plasma enhanced chemical vapour deposition carbon nanotubes/nanofibres - How uniform do they grow?

The ability to grow carbon nanotubes/nanofibres (CNs) with a high degree of uniformity is desirable in many applications. In this paper, the structural uniformity of CNs produced by plasma enhanced chemical vapour deposition is evaluated for field emission applications. When single isolated CNs were deposited using this technology, the structures exhibited remarkable uniformity in terms of diameter and height (standard deviations were 4.1 and 6.3% respectively of the average diameter and height). The lithographic conditions to achieve a high yield of single CNs are also discussed. Using the height and diameter uniformity statistics, we show that it is indeed possible to accurately predict the average field enhancement factor and the distribution of enhancement factors of the structures, which was confirmed by electrical emission measurements on individual CNs in an array.

Multi-colour switching of polymer stabilized chiral nematic liquid crystal devices

We have fabricated a series of polymer stabilized chiral nematic test cells for use as flexoelectro-optic devices. The devices fabricated were based on commercial chiral nematic mixtures which were polymer stabilized so as to enhance the uniformity and stability of the uniform lying helix texture in the cells. During fabrication and test procedures a series of unusual scattering states have been observed within the devices at different viewing angles. The observations made so far indicate that the properties of the scattering state lies somewhere between the focal conic texture and the Grandjean or planar texture and that the devices exhibit both a helical pitch selective reflection and scattering effect. What is even more dramatic is that the wavelength selectivity of the scattering effect can be tuned by an applied field. In addition, we show that it is possible to achieve good uniform lying helix textures from such devices. Moreover, we show that in certain cases the spontaneous alignment of the helix in the plane of the device opens up the possibility of a new mode of switching. Flexoelectric, Redshift, Coloured scattering, Liquid crystal, Polymer-stabilized liquid-crystal;.

Uniform stability of a particle approximation of the optimal filter derivative

Sequential Monte Carlo methods, also known as particle methods, are a widely used set of computational tools for inference in non-linear non-Gaussian state-space models. In many applications it may be necessary to compute the sensitivity, or derivative, of the optimal filter with respect to the static parameters of the state-space model; for instance, in order to obtain maximum likelihood model parameters of interest, or to compute the optimal controller in an optimal control problem. In Poyiadjis et al. [2011] an original particle algorithm to compute the filter derivative was proposed and it was shown using numerical examples that the particle estimate was numerically stable in the sense that it did not deteriorate over time. In this paper we substantiate this claim with a detailed theoretical study. Lp bounds and a central limit theorem for this particle approximation of the filter derivative are presented. It is further shown that under mixing conditions these Lp bounds and the asymptotic variance characterized by the central limit theorem are uniformly bounded with respect to the time index. We demon- strate the performance predicted by theory with several numerical examples. We also use the particle approximation of the filter derivative to perform online maximum likelihood parameter estimation for a stochastic volatility model.