125,810 research outputs found

    Statistics of Titan's South Polar Tropospheric Clouds

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    We present the first long-term study of the behavior of the sporadically observed tropospheric clouds recently discovered near Titan's south pole. We find that one or more small individual cloud systems is present in the 70°-80° south region during every night of observation. These clouds account for 0.5%-1% of Titan's 2.0 μm flux, consistent with a global cloud cover fraction of 0.2%-0.6%. Clouds observed over multiple-night observing periods remained nearly fixed in brightness and position with respect to Titan's surface. The continual presence of south polar clouds is consistent with the hypothesis that surface heating during the long period of continuous polar sunlight at the time of Titan's southern summer solstice drives seasonal convection and cloud formation at the pole

    Similarities in Evasive Behavior of Wolf Spiders (Araneae: Lycosidae), American Toads (Anura: Bufonidae) and Ground Beetles (Coleopterea: Carabidae)

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    (excerpt) While collecting newly metalnorphosed American toads, Bufo anlericanus Holbrook, we have observed that they exhibited evasive behavior similar to that of adults of the wolf spiders, Pardosa saxatilis (Hentz), Pirata insularis Emerton, Pirata arerzicola Emerton, Pirata piratica (Oliver), and adults of the ground beetle, Elaplrrus ruscarius Say. When pursued or disturbed, the spiders, beetles and toads ran across the pound rapidly for short distances (ca. 1-50 cm). They then stopped abruptly and remained motionless. If they were further pursued, this escape sequence was repeated in the same or another direction. Toads and spiders occasionally moved to shallow water to avoid capture. Spiders ran across the water surface whereas the toads swam partially submerged. N\u27e observed this resemblance in evasive behavior on numerous occasions at ponds on the south edge of Carbondale, Illinois (spiders and toads), 1 krn west of Grinnell, Iowa (spiders and toads), and 1.5 km west of Bloomington, Illinois (spiders, toads and beetles). (Specimens were collected for identification from the latter site.

    Effects of protein or amino-acid supplementation on the physical growth of young children in low-income countries.

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    Child growth stunting is common in low-income countries, possibly due to insufficient protein intakes. Most previous studies have concluded that children's protein intakes are adequate in relation to estimated requirements, but these studies did not consider issues of protein digestibility and effects of infection on dietary protein utilization. Using an alternative approach to assess the possible role of protein inadequacy in children's growth restriction, the results of 18 intervention trials in which supplementary protein or amino acids were provided to children ages 6-35 months and growth outcomes were reviewed. Eight studies conducted in hospitalized children recovering from acute malnutrition found that the recommended protein intake levels for healthy children supported normal growth rates, but higher intakes were needed for accelerated rates of "catch-up" growth. Ten community-based studies did not demonstrate a consistent benefit of supplemental protein on children's growth. However, weaknesses in the study designs limit the conclusions that can be drawn from these studies, and additional appropriately designed trials are needed to answer this question definitively. Recommendations for optimizing future study designs are provided herein

    Tentative Detection of the Rotation of Eris

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    We report a multi-week sequence of B-band photometric measurements of the dwarf planet Eris using the {\it Swift} satellite. The use of an observatory in low-Earth orbit provides better temporal sampling than is available with a ground-based telescope. We find no compelling evidence for an unusually slow rotation period of multiple days, as has been suggested previously. A ∼\sim1.08 day rotation period is marginally detected at a modest level of statistical confidence (∼\sim97%). Analysis of the combination of the SwiftSwift data with the ground-based B-band measurements of \citet{2007AJ....133...26R} returns the same period (∼\sim1.08 day) at a slightly higher statistical confidence (∼\sim99%).Comment: Accepted to Icarus 2008-Aug-19. 19 pages total, including 4 figures and 1 tabl

    The Formation of High-Mass Black Holes in Low Mass X-ray Binaries

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    In this note we suggest that high-mass black holes; i.e., black holes of several solar masses, can be formed in binaries with low-mass main-sequence companions, provided that the hydrogen envelope of the massive star is removed in common envelope evolution which begins only after the massive star has finished He core burning. That is, the massive star is in the supergiant stage, which lasts only ∼104\sim 10^4 years, so effects of mass loss by He winds are small. Since the removal of the hydrogen envelope of the massive star occurs so late, it evolves essentially as a single star, rather than one in a binary. Thus, we can use evolutionary calculations of Woosley & Weaver (1995) of single stars. We find that the black holes in transient sources can be formed from stars with ZAMS masses in the interval 20-35\msun. The black hole mass is only slightly smaller than the He core mass, typically \sim 7\msun.Comment: 19 pages, substantial changes, accepted in New Astronom

    Evolution and Merging of Binaries with Compact Objects

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    In the light of recent observations in which short gamma-ray bursts are interpreted as arising from black-hole(BH), neutron-star(NS) or NS-NS mergings we would like to review our research on the evolution of compact binaries, especially those containing NS's. These were carried out with predictions for LIGO in mind, but are directly applicable to short gamma-ray bursts in the interpretation above. Most important in our review is that we show that the standard scenario for evolving NS-NS binaries always ends up with a low-mass BH (LMBH), NS binary. Bethe and Brown (1998) showed that this fate could be avoided if the two giants in the progenitor binary burned He at the same time, and that in this way the binary could avoid the common envelope evolution of the NS with red giant companion which sends the first born NS into a BH in the standard scenario. The burning of He at the same time requires, for the more massive giants such as the progenitors of the Hulse-Taylor binary NS that the two giants be within 4% of each other in ZAMS mass. Applying this criterion to all binaries results in a factor 5 of LMBH-NS binaries as compared with NS-NS binaries. Our scenario of NS-NS binaries as having been preceded by a double He-star binary is collecting observational support in terms of the nearly equal NS masses within a given close binary.Comment: 32 pages, 1 figure, substantial changes from v
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