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"Gem stones"
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Glassteine mit blauen Einschlüssen: Zu einem besonderen Typ mittelalterlicher Glassteine und anderen gläsernen „Edelsteinen
The numerous glass stones coexisting with precious or semi-precious stones on many medieval objects have been mostly neglected by scholars to date. Often they are difficult to distinguish from natural stones, and if their material is recognized as glass, they are regarded as cheap substitutes (or even fakes) and suspected to be added some time later. But there is a special type of glass gems which are without a doubt medieval: those made of colorless glass with blue inclusions. Such glass stones were probably made somewhere in the northwest of present-day Germany because they are found almost exclusively on objects made in those regions during the eleventh through thirteenth centuries. So, the blue-spotted gems are key pieces for our understanding of at least some aspects of the production and use of medieval glass stones.
Journal Article
Amateur gemstone faceting
Amateur faceter Tom Herbst lays out the steps necessary to transform a shapeless lump of rock into a glittering jewel that is unique and valuable. Along the way, he explains not only the \"how\" but also the \"why,\" and provides helpful tips in dealing with many of the pitfalls that confront the beginning gem cutter.
Book
Mineralogy and Petrology of Comet 81P/Wild 2 Nucleus Samples
The bulk of the comet 81P/Wild 2 (hereafter Wild 2) samples returned to Earth by the Stardust spacecraft appear to be weakly constructed mixtures of nanometer-scale grains, with occasional much larger (over 1 micrometer) ferromagnesian silicates, Fe-Ni sulfides, Fe-Ni metal, and accessory phases. The very wide range of olivine and low-Ca pyroxene compositions in comet Wild 2 requires a wide range of formation conditions, probably reflecting very different formation locations in the protoplanetary disk. The restricted compositional ranges of Fe-Ni sulfides, the wide range for silicates, and the absence of hydrous phases indicate that comet Wild 2 experienced little or no aqueous alteration. Less abundant Wild 2 materials include a refractory particle, whose presence appears to require radial transport in the early protoplanetary disk.
Journal Article
Global entrepreneurship and institutions: an introduction
This article is an introduction to the special issue from the 4th Global Entrepreneurship Monitor Research Conference held at Imperial College Business School, London, in 2010. The article has two objectives. The first is to summarize the history of the GEM consortium, some of the contributions that it has delivered, and some challenges and opportunities ahead. The second is to present a summary of the papers in the context of the utility of GEM data in comparative entrepreneurship research.
Journal Article
\The Coat Traps All Your Body Heat\: Heterogeneity as Fundamental to Learning
This article explores heterogeneity as fundamental to learning. Inspired by Bakhtin's notion of heteroglossia, a design team consisting of an experienced classroom teacher and 2 researchers investigated how a class of 3rd and 4th graders came to understand disciplinary points of view on heat, heat transfer, and the particulate nature of matter. Through a series of planned and unplanned encounters, official versions of the Second Law of Thermodynamics and the particulate view of matter were juxtaposed with varied domains of experience of heat transfer and phase change in water. We analyze the children's discourse to examine how they populated these phenomena with meaning and what they learned in the process. We conclude by describing key principles and a conundrum that emerged from this research.
Journal Article
Geography, Rebel Capability, and the Duration of Civil Conflict
Why do some armed civil conflicts last longer than others? Drawing on a contest success function model, we show that geographic factors (such as location, terrain, and natural resources) interact with rebel fighting capacity and together play a crucial role in determining the duration of conflict. Using precisely dated duration data in event history models and geographic data for the conflict location, we find that conflicts located at considerable distance from the main government stronghold, along remote international borders and in regions with valuable minerals last substantially longer. In addition, we find that rebel military capacity in its own right increases the prospects of a civil conflict ending within a short time period. Our findings imply that the distances an army must travel to project power, rebel fighting capacity, and characteristics of conflict region affect how a civil war is fought and who will prevail.
Journal Article