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56 The PCB Magazine • September 2016 This list includes manufacturers of all types of laminate (e.g., low-performance, high-perfor- mance, rigid, and flex laminates). Summary From a PCB fabricator's perspective, epoxy resin supply chain issues are of indirect concern as they become a subset of laminate quality, supply, and cost considerations. However, the performance and availability of epoxy resins and their building blocks affect laminate sup- plier selection profoundly, especially in view of changing base material requirements. Chang- ing market environments with respect to uses of epoxy or copper in markets other than elec- tronics affect prices of these materials for elec- tronic uses but are basically beyond the scope of electronics supply chain management. For example, the largest epoxy resin market is paints and coatings, not electronic applica- tions, and it is difficult to predict the impact of health concerns about Bisphenol A on epoxy resin pricing and availability. Regarding copper, politics in Chile, the largest copper producer in the world, may have an influence on copper pricing but it is probably not worth worrying about it. Likewise, the changing market condi- tions for copper use such as increased demand in electric cars (three times as much as in a standard car, mostly for rotors) or the increased demand for epoxy in wind turbines are worth noting, but they are not actionable items for electronics supply chain managers. PCB Karl Dietz is president of Karl Dietz Consulting LLC. He offers consulting services and tutorials in the field of circuit board and substrate fabrica- tion technology. To view past col- umns or to reach Dietz, click here. Dietz may also be reached by phone at (001) 919-870-6230. EPOXY: SUPPLY CHAIN AND USE IN ELECTRONICS In making decisions about infrastructure de- velopment and resource allocation, city planners rely on models of how people move through their cities, on foot, in cars, and on public trans- portation. Those models are largely based on sur- veys of residents' travel habits. But conducting sur- veys and analyzing their results is costly and time consuming: A city might go more than a decade between surveys. And even a broad survey will cov- er only a tiny fraction of a city's population. In the latest issue of the Proceedings of the Na- tional Academy of Sciences, researchers from MIT and Ford Motor Company describe a new compu- tational system that uses cellphone location data to infer urban mobility patterns. Applying the system to six weeks of data from residents of the Boston area, the researchers were able to quickly as- semble the kind of mod- el of urban mobility pat- terns that typically takes years to build. The system holds the promise of not only more accurate and timely data about urban mobility but the ability to quickly determine whether par - ticular attempts to ad- dress cities' transportation needs are working. "In the U.S., every metropolitan area has an MPO, which is a metropolitan planning organi- zation, and their main job is to use travel surveys to derive the travel demand model, which is their baseline for predicting and forecasting travel de- mand to build infrastructure," says Shan Jiang, a postdoc in the Human Mobility and Networks Lab in MIT's Department of Civil and Environmental En- gineering and first author on the new paper. Inferring Urban Travel Patterns from Cellphone Data

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