The recycling of scrap material has been identified as an important strategy in the larger theory of industrial ecology. Industrial ecology argues that the traditional model of industrial activity needs to be transformed into a ‘closed loop’ industrial ecosystem where used materials (scrap) and by‐products would substitute for virgin materials during production processes. The recycling of scrap material forms part of this larger effort to reduce the overall environmental impact of production and consumption. A key, but as yet, unresolved question in this process is the geographic scale (local, regional, national, global) at which loop closing should take place. This preliminary empirical research examines the export and import geography of the seven largest (by weight) US scrap commodities (iron and steel, paper, plastics, aluminium, copper, nickel and zinc) between 1995 and 2005 to ascertain the extent to which US scrap flows overseas and how that might affect our understanding of how material loops can close. Other than an integrated export and import relationship with Canada, the results suggest that there are two distinct circuits of scrap flows in the USA. The USA exports a substantial portion of the recyclable scrap generated each year to rapidly developing countries, while importing smaller quantities of scrap from the EU. With the major exception of exporting higher value iron and steel scrap to China, the US tends to export lower value scrap and import higher value scrap. In part this reflects imbalances in the supply and demand for scrap between the USA and the developing world, the lack of potentially available scrap and the absence of a robust recycling infrastructure in the developing world. Although such scrap circuits are probably not ideal, the use of US scrap in the developing world is both a realistic and preferable alternative in the short to medium term than virgin production.

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This article surveys the body of investigation related to the location of headquarters and other elite corporate decision‐making activities, a research field known as quaternary location studies. The discussion includes four main sections following an introduction. The first reviews the initial development of headquarters location research from the early 20th century to 1980. The second section discusses contemporary developments and criticisms of the field that have diversified the field beyond its early focus on large‐firm headquarters alone to examine the geography of all activities related to corporate decision making. We posit that incorporation of rapidly growing firms in quaternary research is a key element of this diversification. The third section examines the possibilities for further headquarters location research by making a connection between decision‐making location and the literature of techno‐economic paradigms. The article concludes by summarizing the current state of the field, and argues that a continued diversification of research interests and perspectives is vital to the advancement of quaternary location studies as an important contributor to improved corporate strategies and more effective public policy.

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A clear mathematical relationship exists between object diameter and reduction in measured CT number in HU. This function is independent of exposure parameters and inherent attenuation properties of the objects studied. Future developments include the incorporation of this mathematical model function into quantification software in order to automatically generate a true assessment of measured CT number (HU) corresponding to plaque physical density rho (g/cm(3)). This is a significant development for the accurate, noninvasive classification of noncalcified arterial plaque.

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