386 research outputs found
IRON OXIDATION STATE IN ARCHAEOLOGICAL SILICATIC GLASS: A COMPARISON BETWEEN XANES AND MÖSSBAUER DATA
No full textCompositional analysis of archaeological glasses
No full textAbstract At CoDaWork'03 we presented work on the analysis of archaeological glass compositional data. Such data typically consist of geochemical compositions involving 10-12 variables and approximates completely compositional data if the main component, silica, is included. We suggested that what has been termed 'crude' principal component analysis (PCA) of standardized data often identified interpretable pattern in the data more readily than analyses based on log-ratio transformed data (LRA). The fundamental problem is that, in LRA, minor oxides with high relative variation, that may not be structure carrying, can dominate an analysis and obscure pattern associated with variables present at higher absolute levels. We investigate this further using subcompositional data relating to archaeological glasses found on Israeli sites. A simple model for glass-making is that it is based on a 'recipe' consisting of two 'ingredients', sand and a source of soda. Our analysis focuses on the sub-composition of components associated with the sand source. A 'crude' PCA of standardized data shows two clear compositional groups that can be interpreted in terms of different recipes being used at different periods, reflected in absolute differences in the composition. LRA analysis can be undertaken either by normalizing the data or defining a 'residual'. In either case, after some 'tuning', these groups are recovered. The results from the normalized LRA are differently interpreted as showing that the source of sand used to make the glass differed. These results are complementary. One relates to the recipe used. The other relates to the composition (and presumed sources) of one of the ingredients. It seems to be axiomatic in some expositions of LRA that statistical analysis of compositional data should focus on relative variation via the use of ratios. Our analysis suggests that absolute differences can also be informative
The earliest high-fired glazed ceramics in China: Scientific studies of the proto-porcelain from Zhejiang during the Shang and Zhou periods (c. 1700 – 221 BC)
No full textProto-porcelain, a kind of high-fired lime-rich glazed ceramic, with maturing temperatures in excess of 1200 °C, began to appear in China during the Shang dynasty (c. 1700 to 1027 BC) and became more widespread during the subsequent Zhou dynasty (1027 to 221 BC). Since the 1950s, proto-porcelain has been unearthed from various tombs and sites across the country; most of them in mound tombs and kiln sites in the lower reaches of the Yangtze River. Bodies and glazes of 61 proto-porcelain sherds and 19 non proto-porcelain samples from Shang and Zhou periods production sites in Deqing, Zhejiang province were collected and later analysed by EPMA-WDS to understand the raw materials and to explore the mechanisms behind the formation of these glazes. The results indicate that the bodies of all samples were made from local raw material – porcelain stone. Wood ashes, high in lime and low in potash, were intentionally applied to the proto-porcelain samples, resulting in the formation of lime-rich glazes whose composition were determined by a temperature-controlled mechanism. In contrast, kiln fragments and furniture show a potash-rich fuel vapour glaze, which formed unintentionally during use of the kiln. The firing temperature for most of the proto-porcelain glazes is about the same as the maturing temperature for typical more recent lime glazes, showing that the potters were already at such an early time able to attain sufficiently high temperature in their kilns. The differences in firing temperature and composition underpin the suggestion that the Chinese lime-rich glazes are an independent invention. The glaze-forming process was later replicated in the lab to further test several possible parameters that would be necessary to control for the early potters when producing these glazes on a regular scale. The emergence of these earliest high-fired glazed ceramics has also been contextualised within north and south China during the Shang and Zhou dynasties. The environmental and technological constraints, economic and political organisations, together with religious and belief systems were also taken into consideration to better understand the impact of this innovation of the glazing and firing technology on the later development of Chinese ceramic production
Networks of distribution at the margins of the Empire: late antique glass vessels from the Lower Danube region
No full textThe thesis aims to explore the distribution of glass in the Balkan territories of the late Roman and early Byzantine Empire based on an integrated research on glass vessels from the late 3rd to early 7th centuries AD from three site assemblages in present-day Bulgaria (Dichin, Odartsi, and Serdica). The category of artefacts, i.e. glass vessels, is deliberately chosen since they provide the opportunity to investigate both their ‘archaeology’ (in terms of vessel morpho-typology, decoration, manufacturing techniques, etc.) and their ‘chemistry’ (in terms of chemical composition) as two aspects of research which are not unconnected or contrasted but are complementary to each other. Taking as a framework the model of division in the Roman and late antique glass industry, this study is focused not only on tracing the routes of glass supply from the primary production centres in the East Mediterranean to the Balkans but also on reconstructing the entire chains of distribution of raw glass and finished vessels to the consumers’ sites. Special attention is given to an attempt to identify inter-regional, regional and local networks (as a differentiation in their geographical directions, spatial scale, functional mechanisms, organization, technologies, etc.), and the stratified production and consumers’ needs related to them. From a methodological point of view, the research is based on an integrated classification constructed from artefact research and scientific techniques for compositional characterization of glass (EPMA and LA-ICP-MS analyses). Approaches to technology, exchange, and distribution which have been originally formed in anthropological and economic theory are applied, combined with a detailed understanding of particular historical and archaeological context. The results point to a pattern of glass distribution corresponding to the overall technological and economic processes of Late Antiquity, with shifts in compositions, vessel manufacture and use in early 6th c. AD when significant transformations took place in the Balkans
Technical challenges in the manufacture of opaque turquoise glass in the medieval Islamic world
No full textAnalysis of the glass and glass-working waste
No full textAn assemblage of glass fragments from the Tarbat monastery excavations were analysed by SEM-EDXA. Of the blue glasses, two are modern. The third is a natron-type glass of Roman type which is likely to represent re-use of early material by early medieval craftsmen. The remaining three glasses (all opaque yellow) are unambiguously consistent with early-medieval glass technology. However, it was not possible to establish whether opaque yellow glass was being made at Tarbat, or simply being worked there
Sensor to detect peroxide based explosives
No full textA simple inexpensive sensor that detects hydrogen peroxide vapour that can be used to sniff out peroxide-based explosives, such as those used in the July 2005 bombing of the London transport system, has been developed (F I Bohrer, C N Colesniuc, J Park, I K Schuller, A C Kummel, W C Trogler; J Am Chem Soc, 2008, 130, 3712
Black-box calibration for complex systems simulation
No full textPredicting or measuring the output of complex systems is an important and challenging part of many areas of science. If multiple observations are required for parameter studies and optimization, accurate, computationally intensive predictions or expensive experiments are intractable. This paper looks at the use of Gaussian process based correlations to correct simple computer models with sparse data from physical experiments or more complex computer models. In essence, physics based computer codes and experiments are replaced by fast problem specific statistics based codes. Two aerodynamic design examples are presented. First a cheap two dimensional potential flow solver is calibrated to represent the flow over the wing of an unmanned air vehicle. The rear wing of a racing car is then optimized using rear wing simulations calibrated to include the effects of the flow over the whole car
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