Influence of corona on the voltages induced by nearby lightning onoverhead distribution lines

A model for the calculation of lightning-induced voltages is presented with the aim of assessing the effect of corona when power distribution lines are illuminated by lightning electromagnetic fields. Corona is taken into account by means of dynamic capacitance describing a charge-voltage diagram. Such an equivalent capacitance is then introduced in a model which describes a line illuminated by a lightning electromagnetic field. It is first concluded that the influence of corona on lightning induced overvoltages is of importance only for particularly severe strokes. It is also found that corona acts to increase the magnitude of these overvoltages, contrary to the case of voltages due to direct strokes, which are attenuated by corona. A theoretical explanation of such an amplitude increase is presented. The effect of the ground resistivity is also taken into account in the calculations. The results show that such an effect is in general as important as the effect of corona. This is different from the direct-strike behavior, where corona, when present, affects the surge propagation more than the ground resistivity. This is due to the fact that for the case of induced-voltages, the ground resistivity may affect more strongly the lightning-radiated fields rather than the surge propagation along the line, while corona affects only surge propagation. The need for experimental results to test the theoretical finding of the paper is stressed and some indication is given. Finally, a sensitivity analysis of the induced voltages as a function of the charge-voltage diagram adopted to model corona is also performed     

Size distribution of airborne particulates in monazite dust

A six-stage cascade impactor was used to collect airborne dust particulates in the grinding area of a monazite separation plant. The samples were analysed using particle-induced X-ray emission (PIXE) to determine the elemental concentrations, with special attention to thorium and uranium concentrations. The particle size distribution of the samples containing thorium and uranium were determined. The mass median aerodynamic diameter (MMAD) obtained was 1.15 μm for both elements. The activity median aerodynamic diameter (AMAD) was estimated based on the MMAD. The results are compared with ICRP recommendations for derived air concentrations (DAC) for thorium and uranium in restricted areas.     

The Management of Knowledge during Design and Implementation of Process Technologies

Knowledge and learning play a major part in the successful implementation of process technologies. We suggest that managers of implementation projects can improve the initial performance levels of the process in which a new technology resides by ensuring that useful knowledge, present in the organization at the start of the implementation project, is employed to greatest effect during the design of the modified process and that new learning is not lost. This does not necessarily require major investment in computerized systems – merely exploring what potentially useful knowledge is already available within the organization, or can readily be obtained from external contact, may improve the efficiency of technology implementation. Use of available knowledge can also help to speed up the implementation process by reducing the number of, and time required for, the adaptations necessary to get the process to the desired performance level.     

Auditing NT — Part 2

This second article on NT auditing focuses on controlling users: whether or not they use the system, what they can do once they are in, and how to keep a record of what they have done. As with the operating system configuration that we looked at in the last article, you will need administrator access to review many of the security settings, and to review the security log. You will also be using tools supplied in the NT Resource kit to get listings of information that cannot be effectively scanned online.     

Technology learning for renewable energy: Implications for South Africa's long-term mitigation scenarios

Technology learning can make a significant difference to renewable energy as a mitigation option in South Africa's electricity sector. This article considers scenarios implemented in a Markal energy model used for mitigation analysis. It outlines the empirical evidence that unit costs of renewable energy technologies decline, considers the theoretical background and how this can be implemented in modeling. Two scenarios are modelled, assuming 27% and 50% of renewable electricity by 2050, respectively. The results show a dramatic shift in the mitigation costs. In the less ambitious scenario, instead of imposing a cost of Rand 52/t CO₂-eq (at 10% discount rate), reduced costs due to technology learning turn renewables into negative cost option. Our results show that technology learning flips the costs, saving R143. At higher penetration rate, the incremental costs added beyond the base case decline from R92 per ton to R3. Including assumptions about technology learning turns renewable from a higher-cost mitigation option to one close to zero. We conclude that a future world in which global investment in renewables drives down unit costs makes it a much more cost-effective and sustainable mitigation option in South Africa.     

Comparison between measurements on Rayleigh scattering and form-factor theories for

From our measured differential cross section of Rayleigh scattering, the form factor for momentum transfers in the range was deduced. Data for U, Pb, Pt, W, Sn, Cd, Ag, Mo and Cu at energies from 60 to 662 keV and scattering angles ranging from 5° to 140° were used. In addition, for the region of momenta, experimental data from other authors at higher energies were analyzed. The experimental values obtained were compared with various form-factor theories and limits of validity are established. For the relativistic modified form factor G a good agreement always exists for θ ≤ 65°, independently of energy and atomic number.     

Book reviews

Australian Urban Planning: New Challenges, New Agendas. Brendan Gleeson and Nicholas Low. Allen & Unwin, Sydney, 2000. ISBN 1865082384 (paperback). 273 pp.; bibliography and index. RRP $35.00.

Australian Urban Planning: New Challenges, New Agendas. Review 2.

Equity, Environment, Efficiency: Ethics and Economics in Urban Australia. Patrick Troy (ed.). Melbourne University Press, Melbourne, 2000. ISBN 0522848923 (paperback). 255pp.; bibliography and index. RRP $43.95.

Asian New Urbanism. William S. W. Lim. Select Books, Singapore, 1998. ISBN 9814022012. 250 pp.. RRP $52.00.

Rethinking Australian Citizenship. Wayne Hudson and John Kane (eds). Cambridge University Press, Cambridge, 2000. ISBN 052159670 (paperback), 052159337 9 (hardback). 274pp.; bibliography and index. RRP $34.95 (paperback), $90.00 (hardback).

Community Participation Methods in Design and Planning. Henry Sanoff. John Wiley, New York, 2000. ISBN 0471355453. 306 pp.; bibliography, additional readings and index. RRP $114.95.

Global Spin: The Corporate Assault on Environmentalism. Sharon Beder. Scribe, Melbourne, rev. edn, 2000. ISBN 090801144 (paperback). 336 pp; bibliography and index. RRP $29.95.     

Dyeing machine control using in-line colour measurement. Part 3: Online dyeing quality control

A system is described that controls the dyeing process so as to produce a package within a final unlevelness tolerance in the minimum time. This is achieved by incorporating into the control algorithm a mathematical model capable of predicting the unlevelness in a dyed package from the current state of the system. The use of such a general strategy allows production of dyeings of acceptable quality in minimum time and requires little intervention from the machine operator.     

Antioxidant activity and phenolic contents of Olea europaea L. leaves sprayed with different copper formulations

Olive trees (Olea europaea L. Cv. Cobrançosa) from the northeast of Portugal were sprayed with three different copper formulations [bordeaux mixture (copper sulphate + calcium hydroxide − 20% Cu), copper hydroxide (40% Cu) and copper oxychloride (50% Cu)] to control olive fungal diseases. The residues of copper in olive leaves, harvested at different times, were evaluated by atomic absorption spectrometry. At all the collection times, treated olive leaves had significantly higher copper contents, compared to the control. The different copper amounts in pesticide formulations lowered the leaves contents in total phenols and hence their antioxidant properties. Olive leaves sprayed with copper oxychloride possessed the highest copper levels and the lowest content in phenols, which influenced its antioxidant activity (higher EC₅₀ values for reducing power, scavenging effect on DPPH radicals and inhibition of erythrocyte hemolysis). Leaves without copper residues proved to be a good natural source of antioxidants, giving values comparable to the reference compounds.     

Analog circuits optimization based on evolutionary computation techniques

This paper presents a new design automation tool, based on a modified genetic algorithm kernel, in order to improve efficiency on the analog IC design cycle. The proposed approach combines a robust optimization with corner analysis, machine learning techniques and distributed processing capability able to deal with multi-objective and constrained optimization problems. The resulting optimization tool and the improvement in design productivity is demonstrated for the design of CMOS operational amplifiers.