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Episodic Nature (episodic + nature)
Selected AbstractsMethodology for the evaluation of cumulative episodic exposure to chemical stressors in aquatic risk assessment,ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 4 2000Michael G. Morton Abstract An ecological risk assessment method was developed to evaluate the magnitude, duration, and episodic nature of chemical stressors on aquatic communities. The percent of an ecosystem's species at risk from a designated chemical exposure scenario is generated. In effects assessment, probabilistic extrapolation methods are used to generate estimated safe concentrations (ESCs) for an ecosystem using laboratory toxicity test results. Fate and transport modeling is employed to generate temporal stressor concentration profiles. In risk characterization, area under the curve integration is performed on predicted exposure concentration profiles to calculate a cumulative exposure concentration (CEC) for the exposure event. A correction is made to account for the allowable exposure duration to the stressor ESC. Finally, the CEC is applied to the extrapolation model (curve) of the stressor to predict percent species at risk to the episodic exposure. The method may be used for either prospective or retrospective risk assessments. The results of a retrospective risk assessment performed on the Leadenwah Creek, South Carolina, USA, estuarine community are presented as a case study. The creek experienced periodic episodes of pesticide-contaminated agricultural runoff from 1986 through 1989. Although limited biological data were available for method validation, the risk estimates compared well with the Leadenwah Creek in situ bioassay results. [source] Iron limits primary productivity during spring bloom development in the central North AtlanticGLOBAL CHANGE BIOLOGY, Issue 4 2006C. MARK MOORE Abstract We present in situ biophysical measurements and bioassay experiments that demonstrate iron limitation of primary productivity during the spring bloom in the central North Atlantic. Mass balance calculations indicate that nitrate drawdown is iron (Fe)-limited and that aeolian Fe supply to this region cannot support maximal phytoplankton growth during the bloom. Using a simple simulation model, we show that relief of Fe limitation during the spring bloom can increase nitrate drawdown and, hence, new primary production, by 70%. We conclude that the episodic nature of iron supplied by dust deposition is an important factor controlling the dynamics of the spring bloom. From this, we hypothesize that variability in the timing and magnitude of the spring bloom in response to aeolian Fe supply will affect carbon drawdown and food web dynamics in the central North Atlantic. [source] Population-Based U.S. Study of Severe Headaches in Adults: Psychological Distress and ComorbiditiesHEADACHE, Issue 2 2006Objective.,To examine the associations between severe headaches (SH), psychological distress, and comorbid conditions among U.S. adults. Background.,The lifetime prevalence of headaches is over 90% and headaches, particularly migraines, have been associated with disability, increased healthcare costs, and mood disorders. Methods.,We analyzed data obtained from adults aged 18 years or older (n = 29,828) who participated in the 2002 National Health Interview Survey, an ongoing, computer-assisted personal interview of a representative sample of the U.S. population. Results.,Approximately 15.1% of adults aged 18 years or older reported SH in the previous 3 months. Those reporting such headaches were significantly more likely, than those who did not, to report insomnia, excessive sleepiness, recurrent pain, and depressive or anxiety symptoms during the preceding 12 months. Approximately 88% of those who reported having had SH within the previous 3 months also indicated that they had at least one comorbid medical condition, relative to 67% of those without SH. Conclusion.,Despite their episodic nature, our results suggest that SH are associated with impairments in both physical and mental health. As the presence of SH may serve as an indicator of significant psychological distress and medical comorbidities, eliciting information about their occurrence during a standard medical examination appears to be warranted. [source] Pseudomigraine With Lymphocytic Pleocytosis: A Calcium Channelopathy?HEADACHE, Issue 8 2003Clinical Description of 10 Cases, Genetic Analysis of the Familial Hemiplegic Migraine Gene CACNA1A Objective.,To report the clinical findings of 10 patients diagnosed with pseudomigraine with lymphocytic pleocytosis and the results of mutational analysis of the CACNA1A gene in 8 of these patients. Background.,Pseudomigraine with lymphocytic pleocytosis, also referred to as headache with neurologic deficits and cerebrospinal fluid lymphocytosis (HaNDL), is characterized by episodic transient neurologic dysfunction associated with moderate to severe headache and cerebrospinal fluid lymphocytic pleocytosis. Episodes are recurrent and the condition is self-limiting. The etiology of this sporadic condition remains unknown, but the episodic nature and its ability to be triggered by angiography is somewhat reminiscent of the phenotypic features of familial hemiplegic migraine, a condition caused by mutations in the CACNA1A gene. Design/Methods.,Utilizing retrospective chart review, we describe the clinical features of pseudomigraine with lymphocytic pleocytosis in 10 patients. Whole blood was taken from 8 patients (2 were lost to follow-up) and used for DNA testing. The CACNA1A gene was screened for mutations using heteroduplex analysis and direct DNA sequencing. Results.,Clinical features of pseudomigraine with lymphocytic pleocytosis included transient episodes of weakness, sensory and visual symptoms, aphasia, and confusion lasting minutes up to 4 hours. Sensory symptoms, typically affecting the face and arm, were the most common presentation. Localization of symptoms did not conform to vascular territories. Headache was typically throbbing and most often bilateral. Genetic analysis did not identify any mutations in the CACNA1A gene. Conclusions.,Similarities between familial hemiplegic migraine and pseudomigraine with lymphocytic pleocytosis include recurrent headache with reversible neurologic deficit, cerebrospinal fluid lymphocytic pleocytosis, and triggers such as angiography. Even so, heteroduplex analysis and DNA sequencing failed to identify any sporadic mutations or shared polymorphisms in the exons or the intron/exon boundaries of the CACNA1A gene. These results do not support a role of the CACNA1A gene in the etiology of pseudomigraine with lymphocytic pleocytosis. [source] Linkage disequilibrium and natural selection for mimicry in the Batesian mimic Hypolimnas misippus (L.) (Lepidoptera: Nymphalidae) in the AfrotropicsBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 1 2010IAN J. GORDON On two occasions, on opposite sides of the African continent (Cape Coast, Ghana, and Dar es Salaam, Tanzania), high adult population densities in the polymorphic butterfly Hypolimnas misippus (a presumed mimic of Danaus chrysippus) were followed by linkage disequilibrium in combinations of fore- and hindwing colour patterns. On both occasions, disequilibrium was caused by significant changes in morph frequencies favouring rarer and more mimetic forms. Recaptures were too few for analysis at Dar, although the changes there took place within a single generation and must have been the result of differential survival. Recapture rate data and survival rate estimates at Cape Coast support the hypothesis that selective predation was responsible, as does the observation of synchronous linkage disequilibrium at Dar in the model D. chrysippus, indicating parasitic mimicry. There was clear selection for the perfection of mimicry for forewings at Dar and for hindwings at Cape Coast. Disequilibrium is also reported for two other sites, Legon (Ghana) and Boksburg (South Africa) and, in all four sites, it was associated with an increase in the most mimetic forms. New chemical evidence is presented to support the contention that D. chrysippus is a defended model. Although all the evidence leads to the conclusion that H. misippus is a Batesian mimic of D. chrysippus, many questions remain, particularly with regard to the identity of predators, the episodic nature of selective predation events, and their apparent lack of lasting and significant impact on overall gene frequencies. We conclude that H. misippus presents both challenges and opportunities for studies on mimicry, and we suggest that linkage disequilibrium can be a useful generic indicator for Gestalt predation on polymorphic prey. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100, 180,194. [source] New directions for lifelong learning using network technologiesBRITISH JOURNAL OF EDUCATIONAL TECHNOLOGY, Issue 6 2004Rob Koper The requirements placed on learning technologies to support lifelong learning differ considerably from those placed on technologies to support particular fragments of a learning lifetime. The time scales involved in lifelong learning, together with its multi-institutional and episodic nature are not reflected in today's mainstream learning technologies and their associated architectures. The article presents an integrated model and architecture to serve as the basis for the realisation of networked learning technologies serving the specific needs and characteristics of lifelong learners. The integrative model is called a ,Learning Network' (LN) and its requirements and architecture are explored, together with the ways in which its application can help in reducing barriers to lifelong learning. [source] | ||||||||||