12,727 research outputs found

    Time outdoors and the prevention of myopia

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    Recent epidemiological evidence suggests that children who spend more time outdoors are less likely to be, or to become myopic, irrespective of how much near work they do, or whether their parents are myopic. It is currently uncertain if time outdoors also blocks progression of myopia. It has been suggested that the mechanism of the protective effect of time outdoors involves light-stimulated release of dopamine from the retina, since increased dopamine release appears to inhibit increased axial elongation, which is the structural basis of myopia. This hypothesis has been supported by animal experiments which have replicated the protective effects of bright light against the development of myopia under laboratory conditions, and have shown that the effect is, at least in part, mediated by dopamine, since the D2-dopamine antagonist spiperone reduces the protective effect. There are some inconsistencies in the evidence, most notably the limited inhibition by bright light under laboratory conditions of lens-induced myopia in monkeys, but other proposed mechanisms possibly associated with time outdoors such as relaxed accommodation, more uniform dioptric space, increased pupil constriction, exposure to UV light, changes in the spectral composition of visible light, or increased physical activity have little epidemiological or experimental support. Irrespective of the mechanisms involved, clinical trials are now underway to reduce the development of myopia in children by increasing the amount of time they spend outdoors. These trials would benefit from more precise definition of thresholds for protection in terms of intensity and duration of light exposures. These can be investigated in animal experiments in appropriate models, and can also be determined in epidemiological studies, although more precise measurement of exposures than those currently provided by questionnaires is desirable

    Photic effects on sustained performance

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    Research is described which evaluates manipulating environmental light intensity as a means to attenuate fatigue. A counter balanced, within-subjects design was used to compare nine male subjects exposed to dim (100 lux) and bright (3000 lux) light conditions. Oral temperature values were greater for the bright light group over the dim light condition. Melatonin levels were suppressed by bright light treatment. Also, the frequency of eye blink rate was less for subjects during bright over dim light exposure. Light exposure was without effect on subjective fatigue. However, irrespective of light condition, significant effects on confusion, fatigue, and vigor mood dimensions were found as a result of 30 hour sleep deprivation. The findings suggest that bright lights may be used to help sustain nocturnal activity otherwise susceptible to fatigue. Such findings may have implications for the lighting arrangements on space flights during the subjective night for astronauts

    Ranking structured documents using utility theory in the Bayesian network retrieval model

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    In this paper a new method based on Utility and Decision theory is presented to deal with structured documents. The aim of the application of these methodologies is to refine a first ranking of structural units, generated by means of an Information Retrieval Model based on Bayesian Networks. Units are newly arranged in the new ranking by combining their posterior probabilities, obtained in the first stage, with the expected utility of retrieving them. The experimental work has been developed using the Shakespeare structured collection and the results show an improvement of the effectiveness of this new approach

    Life history differences across a latitudinal gradient in side-blotched lizards (Uta stansburiana)

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    Latitudinal variation has long been known to affect life history. Bergmann and Allen made latitudinal “rules” for mammalian anatomy and Lack, Skutch, and Moreau described differences in life history in birds. Trade-offs occur between important life history processes, like self maintenance (immunity) and other expensive but necessary processes. It is likely that trade-offs occur mostly when resources are limited. Side-blotched lizards have a wide geographic range, and more northerly lizards have been observed to have longer lifespans than their southern conspecifics. We hypothesized that northern sideblotched lizards would invest more energy into self-maintenance compared to shorter-lived southern animals

    Regularities with random interactions in energy centroids defined by group symmetries

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    Regular structures generated by random interactions in energy centroids defined over irreducible representations (irreps) of some of the group symmetries of the interacting boson models sdsdIBM, sdgsdgIBM, sdsdIBM-TT and sdsdIBM-STST are studied by deriving trace propagations equations for the centroids. It is found that, with random interactions, the lowest and highest group irreps in general carry most of the probability for the corresponding centroids to be lowest in energy. This generalizes the result known earlier, via numerical diagonalization, for the more complicated fixed spin (JJ) centroids where simple trace propagation is not possible.Comment: 18 pages, 3 figure

    Developing Effective Faculty Competencies For Teaching International Business Topics

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    Faculty are increasingly called upon to teach topics in international business. To ensure teaching success, faculty need to develop knowledge of countries, international organizations, economies, culture, interpersonal skills in international settings, and foreign business practices. The purpose of the paper is to demonstrate how faculty can obtain the skills and knowledge necessary to teach international topics efficiently and cost effectively
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