1,721,000 research outputs found
A mathematical model for interfacial charge transfer at the semiconductor–dye–electrolyte interface of a dye-sensitised solar cell
No full textA mathematical model for the interfacial charge transfer within dye-sensitised solar cells (DSC) is presented for the semiconductor–dye–electrolyte interface. The model explicitly accounts for each reaction at the interface involving dye molecules, electrolyte species and adsorbed electrons associated with the conduction band surface states of the semiconductor. Additionally, the model accounts for photoelectron injection via singlet and triplet excited dye states. The governing equations can be used to describe the total current produced by the DSC under illuminated and non-illuminated conditions, at steady state. Regular perturbation methods are applied to the model equations to obtain closed form analytic approximations, resulting in approximate solutions that negate the need for numerical solution of the model system. All parameter values associated with the model are obtained from the literature and from experimental data. The presented numerical results and analytic approximations compare favourably to experimental data, capturing the interfacial characteristics of current versus voltage curves of the DSC
Micropolar flow over a porous stretching sheet with strong suction or injection
No full textWe consider self-similar boundary layer flow of a micropolar fluid driven by a porous stretching sheet. For the limiting cases of large suction or injection, an order of magnitude analysis is used to obtain analytic results for the shear stress and the microrotation at the surface. Our analysis reveals how the wall shear stress is significantly affected by two of the parameters in the micropolar model and we indicate how our findings may be of use in technological applications involving micropolar flow
Modeling the stepped potential discharge of primary alkaline battery cathodes
No full textA novel model for the potentiostatic discharge of primary alkaline battery cathodes is presented. The model is used to simulate discharges resulting from the stepped potential electrochemical spectroscopy (SPECS) of primary alkaline battery cathodes cathodes, and the results are validated with experimental data. We show that a model based on a single (or mean) reaction framework can be used to simulate multi-reaction discharge behaviour and we develop a consistent functional modification to the kinetic equation of the model that allows for this to occur. The model is used to investigate the effects that the initial exchange current density, i00, and the diffusion coefficient for protons in electrolytic manganese dioxide (EMD), DH+, have on SPECS discharge. The behaviour observed is consistent with the idea that individual reduction reactions, within the multi-reaction, reduction behaviour of EMD, have distinct i00 and DH+ values
A Finite Difference Equivalent Circuit Approach to Secondary Current Modelling in Annular Porous Electrodes
No full textTackling Diversity with Depth and Breadth: A Paradigm for Modern Engineering Mathematics Education?
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
A least squares based finite volume method for the Cahn-Hilliard and Cahn-Hilliard-reaction equations
No full textA vertex-centred finite volume method (FVM) for the Cahn-Hilliard (CH) and recently proposed Cahn-Hilliard-reaction (CHR) equations is presented. Information at control volume faces is computed using a high-order least-squares approach based on Taylor series approximations. This least-squares problem explicitly includes the variational boundary condition (VBC) that ensures that the discrete equations satisfy all of the boundary conditions. We use this approach to solve the CH and CHR equations in one and two dimensions and show that our scheme satisfies the VBC to at least second order. For the CH equation we show evidence of conservative, gradient stable solutions, however for the CHR equation, strict gradient-stability is more challenging to achieve
A comparison of the Nernst-Planck and Maxwell-Stefan approaches to modelling multicomponent charge transport in electrolyte solutions
No full textAn understanding of charge transport in electrolytic solutions is of vital importance in the modelling and simulation of electrochemically and photoelectrochemically active porous media. To this end, we present two multicomponent charge transport models for an electrolyte system based on the generalized Maxwell-Stefan equations and the dilute solution Nernst-Planck equations. These transport models are used to develop two further models of a simple electrochemical cell consisting of ideally polarizable metal electrodes and a binary electrolyte. The results from the numerical solution of these Maxwell-Stefan and Nernst-Planck models are compared for a range of electrolyte concentrations and the applicability of each model approach is discussed
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