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Sequential Data (sequential + data)

Distribution by Scientific Domains
Life Sciences50%

Selected Abstracts

Are cortisol profiles a stable trait during child development?

AMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 6 2009
Mark V. Flinn
Exposure to stressful experiences can increase vulnerability to adverse health outcomes. A potential neuroendocrine mechanism mediating the link between stress and health is the hypothalamic-pituitary-adrenal (HPA) system, with a key role attributed to the glucocorticoid hormone cortisol. Retrospective and cross sectional clinical studies of humans and experimental studies with nonhuman primates and rodents suggest that traumatic experiences during critical periods in development may have permanent effects on HPA regulation, which in turn can have deleterious effects on health. Here I report results from a continuous 20-year study (1988,2009) of children in a rural community on Dominica. Sequential data on cortisol levels, social stressors, and health in naturalistic, everyday conditions are examined to assess developmental trajectories of HPA functioning. Saliva aliquots were assayed for cortisol in concert with monitoring of growth, morbidity, and social environment. Analyses here include data from 1989 to 1999 for 147 children aged 3,16 years with >100 saliva samples each. Cortisol values were standardized by elapsed time since wake-up. Results do not support the hypothesis that traumatic stress during childhood causes permanent general elevation of cortisol levels. Am. J. Hum. Biol., 2009. © 2009 Wiley-Liss, Inc. [source]

Robust hierarchical state,space models reveal diel variation in travel rates of migrating leatherback turtles

JOURNAL OF ANIMAL ECOLOGY, Issue 5 2006
IAN D. JONSEN
Summary 1Biological and statistical complexity are features common to most ecological data that hinder our ability to extract meaningful patterns using conventional tools. Recent work on implementing modern statistical methods for analysis of such ecological data has focused primarily on population dynamics but other types of data, such as animal movement pathways obtained from satellite telemetry, can also benefit from the application of modern statistical tools. 2We develop a robust hierarchical state,space approach for analysis of multiple satellite telemetry pathways obtained via the Argos system. State,space models are time-series methods that allow unobserved states and biological parameters to be estimated from data observed with error. We show that the approach can reveal important patterns in complex, noisy data where conventional methods cannot. 3Using the largest Atlantic satellite telemetry data set for critically endangered leatherback turtles, we show that the diel pattern in travel rates of these turtles changes over different phases of their migratory cycle. While foraging in northern waters the turtles show similar travel rates during day and night, but on their southward migration to tropical waters travel rates are markedly faster during the day. These patterns are generally consistent with diving data, and may be related to changes in foraging behaviour. Interestingly, individuals that migrate southward to breed generally show higher daytime travel rates than individuals that migrate southward in a non-breeding year. 4Our approach is extremely flexible and can be applied to many ecological analyses that use complex, sequential data. [source]

Shifted factor analysis,Part II: Algorithms

JOURNAL OF CHEMOMETRICS, Issue 7 2003
Sungjin Hong
Abstract We previously proposed a family of models that deal with the problem of factor position shift in sequential data. We conjectured that the added information provided by fitting the shifts would make the model parameters identifiable, even for two-way data. We now derive methods of parameter estimation and give the results of experiments with synthetic data. The alternating least squares (ALS) approach is not fully suitable for estimation, because factor position shifts destroy the multilinearity of the latent structure. Therefore an alternative ,quasi-ALS' approach is developed, some of its practical and theoretical properties are dealt with and several versions of the quasi-ALS algorithm are described in detail. These procedures are quite computation-intensive, but analysis of synthetic data demonstrates that the algorithms can recover shifting latent factor structure and, in the situations tested, are robust against high error levels. The results of these experiments also provide strong empirical support for our conjecture that the two-way shifted factor model has unique solutions in at least some circumstances. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Building an integrated model of information behavior through information journals

PROCEEDINGS OF THE AMERICAN SOCIETY FOR INFORMATION SCIENCE & TECHNOLOGY (ELECTRONIC), Issue 1 2008
Bhuva Narayan
Information behavior models generally focus on one of many aspects of information behavior, either information finding, conceptualized as information seeking, information foraging or information sense-making, information organizing and information using. This ongoing study is developing an integrated model of information behavior. The research design involves a 2-week-long daily information journal self-maintained by the participants, combined with two interviews, one before, and one after the journal-keeping period. The data from the study will be analyzed using grounded theory to identify when the participants engage in the various behaviors that have already been observed, identified, and defined in previous models, in order to generate useful sequential data and an integrated model. [source]