Obsidian hydration dating by infrared spectroscopy: method and calibration

Low temperature (90–190 °C) hydrothermal experiments have been conducted on seven obsidians where composition of the glass varies significantly in the concentration of structural water within the unhydrated bulk material. Infrared transmission spectroscopy was used to track the diffusion of molecular water into the glass surface as a function of time and temperature. Long-term (60–360 days) hydration sequences at 90 °C show a t^0.6 time dependence for the mass uptake of molecular water that forms the hydration layer. The structural water concentration of the unhydrated bulk obsidian is highly correlated with the pre-exponential and activation energy and may be used to estimate the Arrhenius constants. In addition, secondary ion mass spectrometry (SIMS) hydrogen profiling of Napa Glass Mountain obsidian hydrated at 90 °C reveals that the early stages of diffusion exhibit a dynamic behavior that includes a fluctuating hydrogen concentration and a changing diffusion coefficient that slows with time.     

Deletion/Substitution/Addition (DSA) model selection algorithm applied to the study of archaeological settlement patterning

This paper introduces GIS-based statistical methods for the study of settlement patterning in an archaeological context. The main aspect is an improvement over suboptimal stepwise statistical model selection procedures, with the introduction of a Deletion/Substitution/Addition (DSA) algorithm, a systematic model selection algorithm that provides an optimal model choice. The paper also introduces the combined use of Receiving Operator Characteristic (ROC) curves, and variable ranking as key tools aimed at an understanding of settlement patterning causation. An illustrative case study is provided whereby both a purely environmental and a mixed environmental/historical model (based on settlement hierarchy considerations) are investigated.     

Identity,contingency and the urban geography of 'race'

Traditional research in urban geography concerned with issues of 'race' has focused on a series of substantively important issues, yet with conceptual foundation inadequate to the task. Specifically, this body of work has employed outdated and theoretically limited conceptions of identity without sufficient consideration to the importance of historical and geographic contingency. I argue in this essay that topics of traditional concern to urban geography gain new relevance and importance when they are reconsidered and reworked from a social constructivist perspective that takes seriously the importance of identity and contingency. I illustrate my argument with discussions of two aspects of my current research agenda. First, I discuss how research on urban residential segregation gains considerably from a more sensitive encounter with multifaceted notions of identity that explicitly address geographic contingency. Second, I review recent empirical research on US mortgage-lending markets that demonstrates the geographic and class contingency of discrimination. The paper ends with a call for research that employs multiple methodologies.     

A History of the Concept of the Stimulus and the Role it Played in the Neurosciences

The term stimulus, as it was used in science from its earliest appearance in the sixteenth century up to the beginning of the nineteenth century, shows a gradual progress in denotation from the physical object designed to produce nervous and muscular excitation to the generically conceived event or object that initiates sensory or motor activity. To this shift corresponds a shift in the understanding of sensory experience. Johannes Müller's law of specific energy of sensory nerves played a major role in the shift, and Hermann von Helmholtz gave the shift its most thorough philosophical explanation.