Spectroelectrochemical cell for in situ studies of solid oxide fuel cells

Solid oxide fuel cells (SOFCs) are able to produce electricity and heat from hydrogen‐ or carbon‐containing fuels with high efficiencies and are considered important cornerstones for future sustainable energy systems. Performance, activation and degradation processes are crucial parameters to control before the technology can achieve breakthrough. They have been widely studied, predominately by electrochemical testing with subsequent micro‐structural analysis. In order to be able to develop better SOFCs, it is important to understand how the measured electrochemical performance depends on materials and structural properties, preferably at the atomic level. A characterization of these properties under operation is desired. As SOFCs operate at temperatures around 1073 K, this is a challenge. A spectroelectrochemical cell was designed that is able to study SOFCs at operating temperatures and in the presence of relevant gases. Simultaneous spectroscopic and electrochemical evaluation by using X‐ray absorption spectroscopy and electrochemical impedance spectroscopy is possible.     

The Nano-Jackhammer effect in probing near-surface mechanical properties

Because of its ease of implementation and insensitivity to indenter drift, dynamic indentation techniques have been frequently used to measure mechanical properties of bulk and thin film materials as a function of indenter displacement. However, the actual effect of the oscillating tip on the material response has not been examined. Recently, it has been shown that the oscillation used with dynamic indentation techniques alters the measured hardness value of ductile metallic materials, especially at depths less than 200 nm. The alteration in the hardness is due to the added energy associated with the oscillation which assists dislocation nucleation. Atomistic simulations on nickel thin films agree with experiments that more dislocations are nucleated during dynamic indents than with quasi-static indents. Through the analysis of quasi-static and dynamic indents made into nickel single crystals and thin films, a theory to describe this phenomenon is presented. This is coined the Nano-Jackhammer effect, a combination of dislocation nucleation and strain rate sensitivity caused by indentation with a superimposed dynamic oscillation.     

Discrete material optimization of vibrating laminated composite plates for minimum sound radiation

This paper deals with vibro-acoustic optimization of laminated composite plates. The vibration of the laminated plate is excited by time-harmonic external mechanical loading with prescribed frequency and amplitude, and the design objective is to minimize the total sound power radiated from the surface of the laminated plate to the surrounding acoustic medium. Instead of solving the Helmholtz equation for evaluation of the sound power, advantage is taken of the fact that the surface of the laminated plate is flat, which implies that Rayleigh’s integral approximation can be used to evaluate the sound power radiated from the surface of the plate. The novel Discrete Material Optimization (DMO) formulation has been applied to achieve the design optimization of fiber angles, stacking sequence and selection of material for laminated composite plates. Several numerical examples are presented in order to illustrate this approach.     

Nonlinear buckling optimization of composite structures considering “worst” shape imperfections

Nonlinear buckling optimization is introduced as a method for doing laminate optimization on generalized composite shell structures exhibiting nonlinear behaviour where the objective is to maximize the buckling load. The method is based on geometrically nonlinear analyses and uses gradient information of the nonlinear buckling load in combination with mathematical programming to solve the problem. Thin-walled optimal laminated structures may have risk of a relatively high sensitivity to geometric imperfections. This is investigated by the concepts of “worst” imperfections and an optimization method to determine the “worst” shape imperfections is presented where the objective is to minimize the buckling load subject to imperfection amplitude constraints. The ability of the nonlinear buckling optimization formulation to solve the laminate problem and determine the “worst” shape imperfections is illustrated by several numerical examples of composite laminated structures and the application of both formulations gives useful insight into the interaction between laminate design and geometric imperfections.     

Target-fragment angular distributions for the interaction of 86 MeV/A12C with 197Au

Target-fragment angular distributions were measured using radiochemical techniques for 69 different fragments (44 ? A ? 196) from the interaction of 86 MeV/A¹²C with ¹⁹⁷Au. The angular distributions in the laboratory system are forward-peaked with some distributions also showing a backward peaking. The shapes of the laboratory system distributions were compared with the predictions of the nuclear firestreak model. The measured angular distributions differed markedly from the predictions of the firestreak model in most cases. This discrepancy could be due, in part, to overestimation of the transferred longitudinal momentum by the firestreak model, the assumption of isotropic angular distributions for fission and particle emission in the moving frame and incorrect assumptions about how the lightest (A < 60) fragments are produced. No evidence was found for any significant number of target fragments moving sidewise to the beam direction in apparent contradiction to the expectation of hydrodynamical-model calculations. The laboratory-frame angular distributions were transformed into the moving frame using various assumptions about the moving frame velocity. The resulting light-fragment distributions showed an asymmetry in the moving frame indicative of their production in a fast process without the establishment of statistical equilibrium. No evidence was found for any production of the light fragments by a very asymmetric fission mechanism. The fission-fragment distributions were compared to standard formulas and an average fissioning-system angular momentum of $\text{J = 40?50}\text{h}\text{?}$ was deduced. It was not possible to find a moving frame in which the heavy (A > 145) fragment distributions were symmetric about 90°.     

Charged particle spectra in αα and αp collisions at the CERN ISR

Momenta of charged particles produced in inelastic αα, αp, andpp collisions were measured using the Split-Field-Magnet detector at the CERN Intersecting Storage Rings. Inclusive and semi-in-clusive spectra are presented as a function of rapidityy, Feynman-x, and transverse momentump _T . The inclusivey distributions agree well with predictions of the dual parton model; the highest particle densities are reached aty?0 and the momenta of leading protons decrease significantly for increasing total multiplicity. ‘Temperatures’ are equal in αα, αp, andpp interactions. Thep _T distributions depend weakly on the multiplicity.     

Nuclear stopping power in αα anddd collisions

Inelasticαα anddd collisions were studied at a centre-of-mass energy √S _NN=31.2 GeV per nucleon-nucleon collision, using the Split-Field Magnet (SFM) detector at the CERN ISR. In this paper we show the inclusive and semi-inclusive rapidity distributions of protons, compare them with predictions of the Lund model, and calculate the average rapidity loss for participant protons. From the negative particles we calculate the inelasticity of the interaction, the average energy per particle, and the degree of isotropy of the produced hadrons.     

Separation and quantification of components of edible fat utilizing open tubular columns in SFC. Sample introduction by direct injection and SFE coupled on-line to SFC

Summary Geometric isomers of fatty acids were separated by open tubular columns in SFC. The concentration of the analytes varied between 9 and 16 μg mL⁻¹. Quantification of triglycerides with repeatability better than 20% were obtained in a home made SFE-SFC unit. A four point calibration curve for both trimyristin and tripalmitin was developed with correlation coefficients of 0.998 and 0.9998, respectively. The limit of quantification was approximately 3 ng for both components. Supercritical CO₂ as extraction solvent in matrix containing lipids increased the recovery of cholesterol by a factor of three. Using immobilized lipase in on-line SFE-SFC quantification of cholesterol in spray dried egg yolk was possible.     

Study of the pseudo-steady-state kinetics of CO2 hydrate formation and stability

This article describes a dynamic model for formation and stability of CO₂-hydrate on the interface of liquid CO₂(LCO₂) and ocean water at large depths. Experimental results indicate that a thin film of hydrate naturally forms on the interfaces between LCO₂ and water, and inhibits diffusion between the two phases. Experiments further shows that the flux of CO₂ through the hydrate film is dependent of the CO₂-concentration in the ambient sea water. The model proposed here explains these phenomena by introducing four major mechanisms; diffusion of water to the LCO₂-phase, formation of hydrate in the LCO₂-hydrate interface, decay of hydrate in the water-hydrate interface, and diffusion of CO₂ through the water phase. The model explains the CO₂ flux not by diffusion through the hydrate film, but suggest a mechanism of continuous hydrate formation and decay. The overall effect is a “moving,” pseudo-steady-state hydrate film due to transport of CO₂ through the film. The film velocity is dependent of liquid-liquid diffusivity parameters and reaction constant, and lacking experimental values of these parameters, an order–of-magnitude analysis is done by fitting the model to experimentally obtained data for the overall film velocity. The motivation for this work is to elucidate options for CO₂ depositions in deep oceans, of which liquid CO2 sequestration is believed to be one of the most feasible. Spreading of CO₂ from a liquid CO₂-lake and associated lowering of pH in the ecosystem surrounding the lake is of large concern. The work presented here concludes that diffusion of CO₂ in the ocean is largely reduced by the hydrate film and suggests that hydrate formation may alleviate some of the environmental concerns regarding deep ocean sequestration of liquid CO₂. © 1994 John Wiley & Sons, Inc.