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Correlation Models (correlation + models)

Distribution by Scientific Domains

Engineering	50%

Selected Abstracts

Correlation model for spatially distributed ground-motion intensities

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 15 2009
Nirmal Jayaram
Abstract Risk assessment of spatially distributed building portfolios or infrastructure systems requires quantification of the joint occurrence of ground-motion intensities at several sites, during the same earthquake. The ground-motion models that are used for site-specific hazard analysis do not provide information on the spatial correlation between ground-motion intensities, which is required for the joint prediction of intensities at multiple sites. Moreover, researchers who have previously computed these correlations using observed ground-motion recordings differ in their estimates of spatial correlation. In this paper, ground motions observed during seven past earthquakes are used to estimate correlations between spatially distributed spectral accelerations at various spectral periods. Geostatistical tools are used to quantify and express the observed correlations in a standard format. The estimated correlation model is also compared with previously published results, and apparent discrepancies among the previous results are explained. The analysis shows that the spatial correlation reduces with increasing separation between the sites of interest. The rate of decay of correlation typically decreases with increasing spectral acceleration period. At periods longer than 2,s, the correlations were similar for all the earthquake ground motions considered. At shorter periods, however, the correlations were found to be related to the local-site conditions (as indicated by site Vs30 values) at the ground-motion recording stations. The research work also investigates the assumption of isotropy used in developing the spatial correlation models. It is seen using the Northridge and Chi-Chi earthquake time histories that the isotropy assumption is reasonable at both long and short periods. Based on the factors identified as influencing the spatial correlation, a model is developed that can be used to select appropriate correlation estimates for use in practical risk assessment problems. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Mathematical modelling of fire development in cable installations

FIRE AND MATERIALS, Issue 4 2001
P. Van Hees
In 1996 DG XII of the European Commission (Research and Development) approved a 3 year project on the fire performance of electrical cables. Within this FIPEC project, a major part of the work involved correlation and mathematical modelling of flame spread and heat release rate in cable installations. The FIPEC project has developed different levels of testing ranging from a small-scale, cone calorimeter test procedures developed for cables and materials, a full-scale-test procedure based on the IEC 60332-3, but utilizing HRR and SPR measurements, and a real scale test conducted on model cable installations. Links through statistical correlations and mathematical fire modelling between these levels were investigated and the findings are presented in this paper. These links could form the scientific foundations for standards upon which fire performance measurements can be based and for new fire engineering techniques within fire performance based codes. Between each testing level correlation, numerical and mathematical models were performed. All of the models were based on the cone calorimeter test method. The complexity of the models varied from correlation models to advanced physical pyrolysis models which can be used in CFD codes. The results will allow advanced prediction of cable fires in the future. Also a bench mark was established for the prediction of cable performance by means of data obtained from the constituent materials. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Adult health outcomes and their implications for experiences of childhood nutritional stress in Jamaica,

AMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 5 2009
Robin G. Nelson
With insights from the developmental origins of health and disease paradigm (DOHaD), this study explores the impact of childhood nutritional stress on adult health outcomes in Jamaica. Jamaica experienced a lengthy period of political and economic instability beginning in the postcolonial period of the early 1960s. This study tests whether decreased government spending on public resources and limited access to imported food products during the early postcolonial period will be reflected in increased adiposity and body mass index among Jamaican adults. Ethnographic and anthropometric data were collected from individuals born between 1958 and 1988. Variability in health outcomes was assessed using Z -score values for body mass index and summed skinfold thickness measures. Age was employed as both a continuous and categorical independent variable. In partial correlation models controlling for economic status, body mass index values and summed skinfold thickness increased with age. Birth cohort and gender effects were also apparent. Women born between 1959 and 1968 had higher body mass index Z -score values than younger women. Both men and women born between 1959 and 1968 had significantly higher skinfold thickness measures than younger individuals. Individuals born between 1959 and 1968 were children during the immediate postcolonial era in Jamaica. Experiences of nutritional stress during critical developmental periods may have contributed to the observed age-related increases in adipose tissue and body mass index values. This study informs our understanding of the ways that fluctuations in the sociopolitical environment during development can mediate and contribute to poor adult health outcomes. Am. J. Hum. Biol. 2009. © 2009 Wiley-Liss, Inc. [source]

Testing for Spatial Correlation in Nonstationary Binary Data, with Application to Aberrant Crypt Foci in Colon Carcinogenesis

BIOMETRICS, Issue 4 2003
Tatiyana V. Apanasovich
Summary. In an experiment to understand colon carcinogenesis, all animals were exposed to a carcinogen, with half the animals also being exposed to radiation. Spatially, we measured the existence of what are referred to as aberrant crypt foci (ACF), namely, morphologically changed colonic crypts that are known to be precursors of colon cancer development. The biological question of interest is whether the locations of these ACFs are spatially correlated: if so, this indicates that damage to the colon due to carcinogens and radiation is localized. Statistically, the data take the form of binary outcomes (corresponding to the existence of an ACF) on a regular grid. We develop score-type methods based upon the Matern and conditionally autoregressive (CAR) correlation models to test for the spatial correlation in such data, while allowing for nonstationarity. Because of a technical peculiarity of the score-type test, we also develop robust versions of the method. The methods are compared to a generalization of Moran's test for continuous outcomes, and are shown via simulation to have the potential for increased power. When applied to our data, the methods indicate the existence of spatial correlation, and hence indicate localization of damage. [source]