Spatial Diffusion of the HIV/AIDS Epidemic: Modeling Implications and Case Study of AIDS Incidence in Ohio

This paper extends a compartmental epidemiological model for HIV transmission and AIDS incidence to include hierarchical and expansion spatial diffusion. An implication of the resultant model is that hierarchical diffusion causes the large infection growth rates of densely populated areas at the top of the central places hierarchy to “chain” down and dominate small local growth rates during the exponential-growth phase of the epidemic. Also, hierarchical diffusion causes a high transient growth rate in the first few years of a local epidemic. The spatial compartmental model fits observed AIDS incidence spatial diffusion patterns in Ohio reasonably well.     

The Encoding-Error Model of Pathway Completion without Vision

We present a model that accounts for errors in short-cutting to complete a triangular pathway by individuals deprived of visual input. The model assumes that systematic error arises from components of navigation concerned with encoding an internal representation of the pathway, rather than the computation of a homeward trajectory or motor output per se. Subjects' tendency to compress the range of actually produced turns and distances, in comparison to the range of correct values, is attributed to regression toward the mean of encoded values during encoding of segments and turns, in the face of uncertainty about the actual values. Individual-subject variations are attributed to differences in the encoding-function parameters, not to variations in the processes themselves. The model provides excellent accounts of data obtained with triangular pathways but fares less well when pathway complexity increases, at which point errors do not appear to be solely attributable to encoding processes. The sources of error identified by the model are likely to play a role in navigation more generally.     

New Dimensions in Infrastructure Evaluation: The Case of Non-Technical Issues in Intelligent Vehicle-Highway Systems

Traditional infrastructure evaluation focuses primarily on technical criteria, such as the completion of a designated, interconnected system of facilities or a particular project's capacity to reduce costs borne by suppliers or end users. In the contemporary policymaking environment, however, nontechnical criteria are often of great importance in determining the success or failure of a particular infrastructure enterprise. Institutional considerations, for example, can often delay the implementation of a project or undermine its effectiveness. This paper examines the importance of non-technical criteria in infrastructure evaluation through a case study of the implementation of a major highway investment program in advanced communication and control technologies, known as intelligent vehicle -highway systems (IVHS). The case study focuses on the role of institutional issues as well as environmental issues, in the implementation of IVHS in the US. surface transportation system. The case emphasizes, first, the significance of institutional and environmental issues, and second, mechanisms for evaluating these issues in the context of a major infrastructure investment program.     

African metallurgy in the Atlantic world

This paper examines the history of African metallurgy in the era of Atlantic trade. It reports on excavations at the John Reeder foundry site in St Thomas, Jamaica. The transfer of African technologies to the Caribbean reveals the plantation economy's dependence on African technical expertise, not merely slave labour. The comprehensive focus on the Atlantic world also informs archaeological investigations of African-European interaction in West Central Africa. The complexity of Atlantic technological history is characterized by a diverse range of dynamic interactions, rather than the inevitable decline of Africanderived systems. Only by identifying processes as well as products of African technological interaction will it be possible fully to reconstruct the forging of the African past.

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Résumé Cet article examine l'histoire de la métallurgie africaine à l'ère du commerce atlantique. Il rend compte des excavations au site de la fonderie John Reeder, à St Thomas, en Jamaïque. Le transfert des technologies africaines aux Antilles révèle à quel point l'économie de plantation dépendait de l'expertise technique africaine, et pas seulement de l'esclavage. L'accent placé sur le monde atlantique inspire aussi les recherches archéologiques sur l'interaction afro-européenne à l'ouest de l'Afrique centrale. La complexité de l'histoire technologique atlantique est caractérisée par une gamme diverse d'interactions dynamiques, plutôt que par l'inévitable déclin des systèmes africains dérivés. Ce n'est qu'en identifiant les processus aussi bien que les produits de l'interaction technologique africaine qu'il sera possible de reconstruire complètement l'élaboration du passé africain.

     

The Pyramids—Cement or Stone?

Several samples of pyramids from Giza were obtained. The samples were analysed by scanning electron microscopy, electron diffraction by X-rays, powder X-ray diffraction, inductively coupled plasmography, Fourier-transform infrared spectroscopy and other techniques. Some scientists who have recently studied the pyramids have suggested that the pyramids were poured into place, stone by stone. The prevailing theory among Egyptologists is, of course, that the pyramids were built from blocks of natural stone. All of the results obtained during this study directly support the concept that the pyramids are made of limestone and are not cementitious in nature.     

Doing Great Basin archaeology recently: Coping with variability

Great Basin archaeologists spent the 1970s and most of the 1980s tearing down the Desert Culture hypothesis without presenting compelling means for dealing with the empirical variability that made it untenable. Recent research seeks to understand this variability by examining the effect of key variables in extreme environmental contexts, especially in wetlands and at high altitudes, and by developing and refining models of optimality that anticipate variability as the local expression of general evolutionary ecological principles. Research on intraregional and ethnic variability has lagged behind—the former because it is said to be costly, the latter because it is problematical in theory.