Magnetic structures in Ni80Fe20/Ru multilayers

Using polarized neutron reflectivity (PNR) measurements together with associated simulation, magnetic structures of two Ni₈₀Fe₂₀ (1 1 1)/Ru (0 0 0 1) multilayer samples with Ru thickness of 9 and 21 Å were investigated under various external magnetic fields at room temperature. The results reveal the existence of layer thickness, interface roughness, magnetic moment, interlayer coupling angle and non-collinear coupling. The former three are independent of Ru thickness; while the latter two are strongly dependent of Ru thickness.     

Three-dimensional photonic microstructures produced by electric field assisted dissolution of metal nanoclusters in multilayer stacks

The formation of three dimensional (3D) photonic microstructures by the locally selective dissolution of metal clusters embedded in dielectric multilayer stacks is presented. Dissolution of clusters is performed by the simultaneous application of electric field and temperature. The produced photonic structures show a highly tailorable optical behavior that combines the interferential effects of multilayer stacks and the surface plasmon resonance of non-dissolved metal clusters. Due to its feasibility and the possibility to widely modify the optical properties of the resulting structures, the current approach represents a promising method for the production of novel components based on 3D-metallodielectric photonic structures.     

Strategic oscillation for the capacitated hub location problem with modular links

The capacitated single assignment hub location problem with modular link capacities is a variant of the classical hub location problem in which the cost of using edges is not linear but stepwise, and the hubs are restricted in terms of transit capacity rather than in the incoming traffic. We propose a metaheuristic algorithm based on strategic oscillation, a methodology originally introduced in the context of tabu search. Our method incorporates several designs for constructive and destructive algorithms, together with associated local search procedures, to balance diversification and intensification for an efficient search. Computational results on a large set of instances show that, in contrast to exact methods that can only solve small instances optimally, our metaheuristic is able to find high-quality solutions on larger instances in short computing times. In addition, the new method, which joins tabu search strategies with strategic oscillation, outperforms the previous tabu search implementation.     

On the treatment of transient area variation in 1D discontinuous Galerkin simulations of train‐induced pressure waves in tunnels

To simulate the pressure wave generated by a train travelling through a tunnel, we implement a discontinuous Galerkin (DG) method for the solution of the one‐dimensional equations of variable area flow. This formulation uses a spatial discretisation via Legendre polynomials of arbitrary degree, and the resulting semi‐discrete system is integrated using an explicit Runge–Kutta scheme. A simulation of subsonic steady flow in a nozzle shows that the scheme produces stable solutions, without the need for artificial dissipation, and that its performance is optimal for polynomial degrees between 5 and 7. However, when dealing with an unsteady area, we report the presence of numerical oscillations that are not due to the steep pressure fronts in the flow but rather to the projection of a moving area, with piecewise continuous derivatives onto a fixed grid. We propose a reformulation of the DG method to eliminate these oscillations that, put in simple terms, amount to splitting the integrals where the derivatives of the cross‐sectional area are discontinuous into subintegrals where they are continuous. The resulting method does not exhibit oscillations, and it is applied here to two practical cases involving train‐induced pressure waves in a tunnel. The first application is a validation of the DG method through comparison of its computational results with pressure data measured during transit at the Patchway tunnel near Bristol (UK). The second application is a study of the influence of the nose shape and length on the pressure wave gradients responsible for sonic boom at tunnel exit portals to show that the proposed modification is able to deal with realistic train shapes. Copyright © 2012 John Wiley & Sons, Ltd.     

‘One‐Touch’ Voltammetry of Microparticles for the Identification of Corrosion Products in Archaeological Lead

Voltammetry of microparticles is applied to the identification of lead corrosion products by means of an essentially non‐invasive ‘one‐touch’ technique based on the use of graphite pencil. This methodology permits the mechanical attachment of few nanograms of sample from the surface of lead archaeological artefacts to a paraffin‐impregnated graphite electrode, which, upon immersion in aqueous electrolytes, provides distinctive voltammetric responses for litharge and cotunnite‐ anglesite‐, cerusite‐based corrosion products. The reported method is applied to the identification of corrosion products in archaeological lead pieces from different Iberian sites in Valencia (Spain).     

Differential pulse polarographic determination of traces of iron in solar-grade silicon

Iron is determined, after volatilization of the matrix as hexafluorosilicic acid, by means of the polarographic iron(III) wave in a 0.1 M triethanolamine—0.1 M potassium bromate—0.5 M sodium hydroxide medium. Differential pulse polarography provides a detection limit of about 0.15 μg g^-1 with a precision of 1–2% and linear calibration graphs up to 0.5 μg Fe(III) ml^-1.     

Application of the voltammetry of microparticles for dating archaeological lead using polarization curves and electrochemical impedance spectroscopy

The application of the voltammetry of microparticles methodology to date archaeological lead artifacts, based on the time-dependent formation of different layers of lead oxides, whose relative amount can be estimated from polarization curves and electrochemical impedance spectroscopy (EIS), is presented. This approach is complemented by additional data using square wave voltammetry data. Calibration of the method was performed with the help of a series of well-documented, lead pieces from the funds of different Spanish museums, covering since the 7th century BC to nowadays.     

Gadolinium doped Ceria nanocrystals synthesized from mesoporous silica

Highly crystalline and thermally stable gadolinium doped ceria (GDC) particles have been synthesized by hard template route for the first time. This oxide is being recognized as an intermediate temperature (500–700 °C) electrolyte material for applications in solid-oxide fuel cells. The GDC particles show high crystallinity and nanometric size (2.83 ± 0.05 nm in diameter) and Raman analyses confirm the formation of the solid solution instead of a CeO₂ and Gd₂O₃ mixture. EDX and EELS studies indicate a stoichiometry coherent with the Gd_0.2Ce_0.8O_1.9 phase. The synthesized nanometric powder is expected to be used in solid oxide fuel cells as well as in the catalytic treatment of automobile exhaust fumes.

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Assessment of added mass effects on flutter boundaries using the Leishman–Beddoes dynamic stall model

We consider the dynamics of a typical airfoil section both in forced and free oscillations and investigate the importance of the added mass terms, i.e. the second derivatives in time of the pitch angle and plunge displacement. The structural behaviour is modelled by linear springs in pitch and plunge and the aerodynamic loading represented by our interpretation of the state-space version of the Leishman–Beddoes semi-empirical model. The added mass terms are often neglected since this leads to an explicit system of ODEs amenable for solution using standard ODE solvers. We analyse the effect of neglecting the added mass terms in forced oscillations about a set of mean angles of incidence by comparing the solutions obtained with the explicit and implicit systems of ODEs and conclude that their differences amount to a time lag that increases at a constant rate with increases of the reduced frequency. To determine the effect of the added mass terms in free oscillations, we introduce a spring offset angle to obtain static equilibrium positions at various degrees of incidence. We analyse the stability of the explicit and implicit aeroelastic systems about those positions and compare the locations of the respective flutter points calculated as Hopf bifurcation points. For low values of the spring offset angle, added mass effects are significant for low values of the mass ratio, or the ratio of natural frequencies, of the aeroelastic system. For high values of the spring offset angle, corresponding to stall flutter, we observe that their effect is greater for large values of the mass ratio.