浪涌抑制器保护电子产品免受高压瞬态影响

在汽车和工业应用中，常常遇到持续时间从几微秒到几百毫秒的高压电源尖峰。这些系统中的电子产品不仅必须耐受瞬态电压尖峰而不被损坏，而且在很多情况下还必须在出现电压尖峰时自始至终保证可靠工作。在电源通过长导线分配的系统中，负载步进（即负载电流突然变化）会引起严重的瞬态。尤其引人注意的是负的负载步进，这时负载电流从较大值降低为较小值。负的dl／dt引起导线寄生电感，产生正向高压尖峰，这可能造成由同一条导线供电的周围器件的损坏.     

Histogram approaches for lossy compression of digital holograms of three-dimensional objects.

We present a novel nonuniform quantization compression technique-histogram quantization-for digital holograms of 3-D real-world objects. We exploit a priori knowledge of the distribution of the values in our data. We compare this technique to another histogram based approach: a modified version of Max's algorithm that has been adapted in a straight-forward manner to complex-valued 2-D signals. We conclude the compression procedure by applying lossless techniques to our quantized data. We demonstrate improvements over previous results obtained by applying uniform and nonuniform quantization techniques to the hologram data.     

Early Photography in Samoa

Abstract

The history of photography in Samoa, a small group of islands in the Western Pacific, suggests, in microcosm, the history of ‘exotic’ photography throughout the world in the period of imperial expansion. The romantic myths of the South Seas, coupled with the islands' practical significance to their colonizers as coaling stations, navy bases and a source of raw materials and cheap labour, encouraged outside interest and assured a market for the products of many kinds of photographers. As early as the 1880s, amateurs on holiday, scientists in the field, and itinerant professionals had passed through Samoa, taking a wide variety of images away with them. By the 1890s, Apia, Samoa's largest town, was home to three resident photographers. Their work was put to conventional private use there for portraits, wedding pictures and the like, and was widely distributed overseas as novelty carter-de-visite, cabinet-size, and full-plate albumen prints, as souvenir postcards and gravures, and as half-tone illustrations in newspapers and magazines. In addition to documenting a society undergoing great change, early photographs of Samoa are often strikingly beautiful, appealing to our appreciation of the exotic and romantic, much as they were intended to do for their foreign audiences one hundred years ago.     

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.     

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.     

The prevention of mindlessness.

We conducted three experiments to assess the hypothesis that mindlessness could be prevented with a simple linguistic variation. Subjects in the first two experiments were either introduced to new objects conditionally (e.g., this could be an X) or unconditionally (e.g., this is an X), and the objects used were either unfamiliar or familiar. In each study a different need was then generated for which the object in question was not explicitly suited but could fulfill. Only those subjects in the conditional-unfamiliar group gave the creative response and met the need. When subjects were asked explicitly to generate novel uses for the target items, they had no difficulty doing so. However, given the way we are traditionally taught, it simply does not occur to us to think creatively unless explicitly instructed to do so. In the third experiment we introduced an unfamiliar item in one of three ways. In addition to the groups used in the earlier experiments, we added a group that was led to believe that the object was identifiable (unconditional) but was currently unknown. We also added a second need to determine whether the original conditional group truly learned conditionally or if they were in search of an absolute understanding of the target object. Significantly more of the subjects in the conditional group gave the creative response to both needs. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The fracture behaviour of two Co-Mo-Cr-Si wear resistant alloys (“Tribaloys”)

The room temperature modulus of rupture (MOR) and the plane strain fracture toughness (K _IC) of two Co-Mo-Cr-Si wear resistant alloys in various microstructure conditions have been determined. The modulus of rupture varied from 304 to 927 MN m^–2 and as such was more structure sensitive thanK _IC, which was in the range 15 to 26 MN m^–3/2 for all conditions of the alloys. The best combination of room-temperature properties was associated with an f c c solid solution whereas h c p solid solution with a Widmanstätten precipitate produced the poorest properties. The industrial significance of these results are discussed.