3,790 research outputs found

    Jets, knots and tails in planetary nebulae: NGC 3918, K 1-2 and Wray 17-1

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    We analyze optical images and high-resolution, long-slit spectra of three planetary nebulae which possess collimated, low-ionization features. NGC 3918 is composed of an inner, spindle-shaped shell mildly inclined with respect to the plane of the sky. Departing from the polar regions of this shell, we find a two-sided jet expanding with velocities which increase linearly with distance from 50 to 100 km/s. The jet is probably coeval with the inner shell (with the age of approximately 1000 D yr, where D is the distance in kpc), suggesting that its formation should be ascribed to the same dynamical processes which also shaped the main nebula, and not to a more recent mass loss episode. We discuss the formation of the aspherical shell and jet in the light of current hydrodynamical and magnetohydrodynamical theories. K 1-2 is a planetary nebula with a close binary nucleus which shows a collimated string of knots embedded in a diffuse, elliptical shell. The knots expand with a velocity similar to that of the elliptical nebula (25 km/s), except for an extended tail located out of the main nebula, which linearly accelerates up to 45 km/s. We estimate an inclination on the line of the sight of 40 degres for the string of knots; once the orientation of the orbit is also determined, this information will allow us to test the prediction of current theories of the occurrence of polar jets from close binary systems. Wray 17-1 has a complex morphology, showing two pairs of low-ionization structures located in almost perpendicular directions from the central star, and embedded in a large, diffuse nebula. The two pairs show notable similarities and differences, and their origin is very puzzling.Comment: 20 pages plus 10 figures. ApJ recently published (ApJ 523, 721 (1999)

    Metal-Semiconductor Interfaces in Thin-Film Transistors

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    The metal-semiconductor interface in thin-film transistors (TFTs) is one of the bottlenecks on the development of these devices. Although this interface does not play an active role in the transistor operation, a low-quality interface can be responsible for a low performance operation. In a-Si TFTs, a doped film can be used to improve this interface, however, in other TFT technologies, there is no doped film to be used. In this chapter, some alternatives to improve this interface are analysed. Also, the influence of this interface on the electrical stability of these devices is presented

    Regional Variations in Physical Fitness and Activity in Healthy and Overweight Ecuadorian Adolescents

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    Background: Insufficient physical activity (PA) and excessive sedentary behavior (SB) are the main contributors to adolescent obesity. However, it is uncertain whether recent economic growth and urbanization in Ecuador are contributing to an obesogenic environment. This study assessed the relationships among fitness, PA, SB, and perceived social support for PA in adolescents from urban (Quito) and rural (Loja) Ecuador. Methods: Fitness was estimated using 3-min step test and PA and SB participation and social support for PA were self-reported in 407 adolescents. T-tests and analysis of variance assessed differences by sex, obesity status, and region of Ecuador. Pearson correlations assessed relationships among PA, SB, fitness, and social support. Results: Males and rural adolescents (48.3 ± 9.4 and 47.1 ± 9.6 mL/kg/min) were more fit than females and urban adolescents (41.1 ± 7.5 and 39.7 ± 6.1 mL/kg/min). Fitness was negatively correlated with obesity only in rural Ecuador. Few adolescents reported ≥60 min/day of PA (8.4%) or ≤2 h/day of SB (30.2%), with greater SB participation in rural Ecuador. Weak correlations were observed among fitness, PA, SB, and parental/peer support for PA (r = −0.18 to 0.19; p \u3c 0.05). Conclusion: While fitness varied by sex, weight status, and region, SB participation and parent/peer support for PA, not PA participation itself, predicted fitness in rural Ecuadorean adolescents

    The International Working Group on Neurotransmitter related Disorders (iNTD): A worldwide research project focused on primary and secondary neurotransmitter disorders

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    INTRODUCTION: Neurotransmitters are chemical messengers that enable communication between the neurons in the synaptic cleft. Inborn errors of neurotransmitter biosynthesis, breakdown and transport are a group of very rare neurometabolic diseases resulting in neurological impairment at any age from newborn to adulthood. METHODS AND RESULTS: The International Working Group on Neurotransmitter related Disorders (iNTD) is the first international network focusing on the study of primary and secondary neurotransmitter disorders. It was founded with the aim to foster exchange and improve knowledge in the field of these rare diseases. The newly established iNTD patient registry for neurotransmitter related diseases collects longitudinal data on the natural disease course, approach to diagnosis, therapeutic strategies, and quality of life of affected patients. The registry forms the evidence base for the development of consensus guidelines for patients with neurotransmitter related disorders. CONCLUSION: The iNTD network and registry will improve knowledge and strengthen research capacities in the field of inborn neurotransmitter disorders. The evidence-based guidelines will facilitate standardized diagnostic procedures and treatment approaches
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