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Two high voltage direct current transmission line circuits have been simulated in the PSIM software, one employing the Individual Phase Control scheme and the other, Equidistant Pulse Control scheme. This paper presents the circuitry employed in the two simulations and the results obtained from both. It is shown that the circuit employing the former scheme suffers from an excess of non-characteristic harmonics when operating with a weak AC system whereas the latter can work on weak AC systems without problems of harmonic instability because it generates firing pulses independent of the AC source. The implementation of the two schemes clearly demonstrates how one is dependent on the feedback from the source whilst the other utilizes a Phase Locked Loop to circumvent this problem.

In recent times, the term ‘local economic development’ has been conceptualised and introduced as a bottom-up participatory development strategy in Ghana. It is intended to be implemented at the district level to facilitate the revitalisation of the local economy and create jobs for local residents. Using in-depth interviews and the analysis of relevant policy documents, this paper evaluates efforts aimed at institutionalising the practice in local institutional frameworks and development planning practice in the country. The paper found out that processes aimed at institutionalising contemporary local economic development practice in Ghana are not making any meaningful impact. Institutional frameworks such as the structuring of development policymaking and planning in the country are still rigid and promote bureaucratic top-down development decision-making processes. Similarly, the promotion of a meaningful bottom-up decentralised planning system is only a well-packaged talk by policymakers in the country. Evidence shows that there is a clear lack of political will to implement reforms, particularly the new decentralisation policy that seeks to make District Assemblies in Ghana responsive to local economic development promotion. There is the need for a conscious effort towards making local economic development practice matter in national and local development endeavour in Ghana.

A model for electrochemical doping of polyaniline taking into account the presence of protons and polarons in the polymer bulk is considered. The essential feature of this model is the account of the interactions between these species. The expressions for oxidation and protonation isotherms and the corresponding voltammograms over a wide range of electrode potential and solution pH are derived. The theoretical results seem to be in qualitative agreement with the literature experimental data.

Abstract To fulfill further eco-efficiency requirements, concrete technology practitioners are currently challenged to provide concretes with tailored properties to meet sustainability and resilience requirements for infrastructural systems. As such, nano-engineering concrete by incorporating nanocellulose materials (NCM) can disclose new research directions for tailoring properties necessary for sustainable cement composites. The current study investigates the performance of cement systems incorporating cellulose filaments (CF) and aims at fostering new understanding of the macroscale mechanical performance with a top-down multiscale approach. The study investigates the mechanical performance (i.e., compressive strength, flexural capacity, and elastic modulus) at macroscale of cement pastes incorporating CF at dosages of 0.0%, 0.05%, 0.10%, 0.20% and 0.30 wt%. The findings are supplemented by microstructure investigations, namely, degree of hydration and micromechanical properties (hardness, indentation modulus, and contact creep modulus) of microstructure phases using nanoindentation coupled with quantitative energy-dispersive spectroscopy (NI-QEDS). Results showed that CF incorporation resulted into 15–25% enhancements in macro-mechanical properties with up to 74% enhancement in flexural toughness. These enhancements are driven by a twofold microstructure change, i.e.: increased degree of hydration (15%) and higher micromechanical properties of C-S-H matrix (∼12–25%). CF is a promising nano-reinforcement for engineering cement composites with superior mechanical performance, while promoting the development of ecological construction materials.

With an increased interest in applications that require a clean background image, such as video surveillance, object tracking, street view imaging and location-based services on web-based maps, multiple algorithms have been developed to reconstruct a background image from cluttered scenes. Traditionally, statistical measures and existing image quality techniques have been applied for evaluating the quality of the reconstructed background images. Though these quality assessment methods have been widely used in the past, their performance in evaluating the perceived quality of the reconstructed background image has not been verified. In this work, we discuss the shortcomings in existing metrics and propose a full reference Reconstructed Background image Quality Index (RBQI) that combines color and structural information at multiple scales using a probability summation model to predict the perceived quality in the reconstructed background image given a reference image. To compare the performance of the proposed quality index with existing image quality assessment measures, we construct two different datasets consisting of reconstructed background images and corresponding subjective scores. The quality assessment measures are evaluated by correlating their objective scores with human subjective ratings. The correlation results show that the proposed RBQI outperforms all the existing approaches. Additionally, the constructed datasets and the corresponding subjective scores provide a benchmark to evaluate the performance of future metrics that are developed to evaluate the perceived quality of reconstructed background images.

Recent work by the present authors has presented a redundant, reconfigurable ball wheel mechanism, and the motion of an associated omnidirectional platform was simulated on flat terrain (Lee et al., 2007). The outdoor environment usually contains uneven terrain, and in this article, motion of an omnidirectional-wheeled mobile platform based on three ball wheel drive mechanisms is studied when the platform moves on uneven terrain that is modeled as a smooth surface. A critical issue that arises for uneven terrain is that the point of contact of the wheel and the terrain is changing. This introduces three more degrees of freedom, which cannot be directly controlled and should also be considered in uneven terrain motion. Herein, Euler-Rodrigues parameters are used to derive the necessary transformations, and Montana's contact equations with the geometric parameters of the terrain are used for tracing the contact point. Simulation results are then presented for motion on flat terrain and both concave and convex spherically shaped terrain. The results clearly show the effectiveness of the proposed method, which can accommodate other more complex terrains provided that the surface configuration is given in an orthogonal coordinate chart.

The specific current-voltage-temperature dependence of space-charge-limited conduction processes in semiconductors and insulators is largely determined by the distribution in energy of traps within the band gap. A linear dependence of current-density on the square of the applied voltage, may be alternatively interpreted in terms of either a single discrete trapping level, or of an exponential trap distribution. The two types of trapping behavior may be distinguished using measurements of the variation of current with temperature for a range of different constant voltages.