The practice of crime prevention: design principles for more effective security governance

South Africa has had a comprehensive crime prevention policy agenda for some time in the form of the 1996 National Crime Prevention Strategy and the 1998 White Paper on Safety and Security. Despite this, prevention has remained very much a second cousin within the South African criminal justice family, notwithstanding the fact that there is widespread agreement that it warrants far more attention. In this article we briefly review some of the principal obstacles to effective crime prevention. Our understanding of ‘crime prevention’ is a broad one – it involves simply asking the question: How can we reduce the likelihood of this happening again? This question opens up a range of preventative possibilities. Whether they are of a socio-economic, environmental or law enforcement nature depends on the nature of the (crime) problem. On the basis of our analysis, we propose three design principles to be followed if we, South Africans are to establish crime prevention as a central focus of our security governance. These design principles articulate what might be thought of as ‘best thinking’ rather than ‘best practice’

Batteries: Imaging degradation

The degradation and failure of Li-ion batteries is strongly associated with electrode microstructure change upon (de)lithiation. Now, an operando X-ray tomography approach is shown to correlate changes in the microstructure of electrodes to cell performance, and thereby predict degradation pathways

On the origin and application of the Bruggeman correlation for analysing transport phenomena in electrochemical systems

The widely used Bruggeman equations correlate tortuosity factors of porous media with their porosity. Finding diverse application from optics to bubble formation, it received considerable attention in fuel cell and battery research, recently. The ability to estimate tortuous mass transport resistance based on porosity alone is attractive, because direct access to the tortuosity factors is notoriously difficult. The correlation, however, has limitations, which are not widely appreciated owing to the limited accessibility of the original manuscript. We retrace Bruggeman's derivation, together with its initial assumptions, and comment on validity and limitations apparent from the original work to offer some guidance on its use

X-ray attenuation properties of commonly employed solid oxide fuel cell materials

X-ray nano CT has been vastly applied to study the microstructure of solid oxide fuel cell (SOFC) electrodes. One widely accepted indicator of electrochemical performance is the triple phase boundary (TPB): a location where the three materials responsible for ionic, electronic and gas-phase reactant transport are in contact. X-ray absorption tomography has been used extensively in the characterisation of these TPBs, utilising the different attenuation properties of the constituent materials. Here we present a quantitative comparison of the attenuation properties for elements commonly employed in solid oxide fuel cell materials

Tortuosity in electrochemical devices: a review of calculation approaches

The tortuosity of a structure plays a vital role in the transport of mass and charge in electrochemical devices. Concentration polarisation losses at high current densities are caused by mass transport limitations and are thus a function of microstructural characteristics. As tortuosity is notoriously difficult to ascertain, a wide and diverse range of methods have been developed to extract the tortuosity of a structure. These methods differ significantly in terms of calculation approach and data preparation techniques. Here, a review of tortuosity calculation procedures applied in the field of electrochemical devices is presented to better understand the resulting values presented in the literature. Visible differences between calculation methods are observed, especially when using porosity–tortuosity relationships and when comparing geometric and flux-based tortuosity calculation approaches

Scoping study on the prospects for sustainable tree crop development in Sub-Saharan Africa. A paper prepared for the World Bank

The objectives of this short scoping study are to identify key issues for development of the tree crop sector particularly smallholder production, and to draw attention to opportunities for World Bank funding of tree crop initiatives as a focus for possible productive investment in Sub-Saharan Africa, and for in-depth examination in a wider study. The study looks particularly at issues relevant to new crop development/replanting and those arising from liberalisation

Optimal integrated energy systems design incorporating variable renewable energy sources

The effect of variability in renewable input sources on the optimal design and reliability of an integrated energy system designed for off-grid mining operation is investigated via a two-stage approach. Firstly, possible energy system designs are generated by solving a deterministic non-linear programming (NLP) optimization problem to minimize the capital cost for a number of input scenarios. Two measures of reliability, the loss of power supply probability (LPSP) and energy index of reliability (EIR), are then evaluated for each design based on the minimization of the external energy required to satisfy load demands under a variety of input conditions. Two case studies of mining operations located in regions with different degrees of variability are presented. The results show that the degree of variability has an impact on the design configuration, cost and performance, and highlights the limitations associated with deterministic decision making for high variability systems