294 research outputs found
Planetary Trojans - the main source of short period comets?
We present a short review of the impact regime experienced by the terrestrial
planets within our own Solar system, describing the three populations of
potentially hazardous objects which move on orbits that take them through the
inner Solar system. Of these populations, the origins of two (the Near-Earth
Asteroids and the Long-Period Comets) are well understood, with members
originating in the Asteroid belt and Oort cloud, respectively. By contrast, the
source of the third population, the Short-Period Comets, is still under debate.
The proximate source of these objects is the Centaurs, a population of
dynamically unstable objects that pass perihelion between the orbits of Jupiter
and Neptune. However, a variety of different origins have been suggested for
the Centaur population. Here, we present evidence that at least a significant
fraction of the Centaur population can be sourced from the planetary Trojan
clouds, stable reservoirs of objects moving in 1:1 mean-motion resonance with
the giant planets (primarily Jupiter and Neptune). Focusing on simulations of
the Neptunian Trojan population, we show that an ongoing flux of objects should
be leaving that region to move on orbits within the Centaur population. With
conservative estimates of the flux from the Neptunian Trojan clouds, we show
that their contribution to that population could be of order ~3%, while more
realistic estimates suggest that the Neptune Trojans could even be the main
source of fresh Centaurs. We suggest that further observational work is needed
to constrain the contribution made by the Neptune Trojans to the ongoing flux
of material to the inner Solar system, and believe that future studies of the
habitability of exoplanetary systems should take care not to neglect the
contribution of resonant objects (such as planetary Trojans) to the impact flux
that could be experienced by potentially habitable worlds.Comment: 16 pages, 4 figures, published in the International Journal of
Astrobiology (the arXiv.org's abstract was shortened, but the original one
can be found in the manuscript file
Light attenuation characteristics of glacially-fed lakes
Transparency is a fundamental characteristic of aquatic ecosystems and is highly responsive to changes in climate and land use. The transparency of glacially-fed lakes may be a particularly sensitive sentinel characteristic of these changes. However, little is known about the relative contributions of glacial flour versus other factors affecting light attenuation in these lakes. We sampled 18 glacially-fed lakes in Chile, New Zealand, and the U.S. and Canadian Rocky Mountains to characterize how dissolved absorption, algal biomass (approximated by chlorophyll a), water, and glacial flour contributed to attenuation of ultraviolet radiation (UVR) and photosynthetically active radiation (PAR, 400–700 nm). Variation in attenuation across lakes was related to turbidity, which we used as a proxy for the concentration of glacial flour. Turbidity-specific diffuse attenuation coefficients increased with decreasing wavelength and distance from glaciers. Regional differences in turbidity-specific diffuse attenuation coefficients were observed in short UVR wavelengths (305 and 320 nm) but not at longer UVR wavelengths (380 nm) or PAR. Dissolved absorption coefficients, which are closely correlated with diffuse attenuation coefficients in most non-glacially-fed lakes, represented only about one quarter of diffuse attenuation coefficients in study lakes here, whereas glacial flour contributed about two thirds across UVR and PAR. Understanding the optical characteristics of substances that regulate light attenuation in glacially-fed lakes will help elucidate the signals that these systems provide of broader environmental changes and forecast the effects of climate change on these aquatic ecosystems
Evolution of IGF-1 in children born small for gestational age and with growth retardation, treated by growth hormone adapted to IGF-1 levels after 1 year
AIM: This study was designed to estimate the percentage of growth hormone (GH)-treated children born small for gestational age (SGA), with serum IGF-1 >2 SDS before and after GH dose adaptation. METHODS: SGA boys aged 4-9 and girls aged 4-7 with a height <-2 SDS and an annual growth rate below the mean received a subcutaneous GH dose of 57 mug/kg/day for 2 years. The GH dose was to be decreased by 30% in children with serum IGF-1 >2 SDS at 12 months and on the previous sample. The GH dose could be reduced a second time to 35 mug/kg.day. IGF-1 and IGFBP-3 dosages were centralized. RESULTS: Among the 49 (21 boys) children included in the study, 8 (16.3%) had an IGF-1 >2 SDS consecutively at 9 and 12 months (95% CI 7.3, 29.7). The GH dose was decreased in 6/8 children. However, IGF-1 levels were elevated at several nonconsecutive determinations in 45% (95% CI 28.4, 56.6) of the patients. CONCLUSION: A high IGF-1 level is observed in 45% of the GH SGA-treated children with a relatively high dose of GH. A 30% reduction in the GH dose causes a decrease in IGF-1 below 2 SDS in most children
Signatures of Habitats and Life in Earth’s High-Altitude Lakes: Clues to Noachian Aqueous Environments on Mars
Relation of gallbladder function and Helicobacter pylori infection to gastric mucosa inflammation in patients with symptomatic cholecystolithiasis
Background. Inflammatory alterations of the gastric mucosa are commonly caused by Helicobacter pylori (Hp) infection in patients with symptomatic gallstone disease. However, the additional pathogenetic role of an impaired gallbladder function leading to an increased alkaline duodenogastric reflux is controversially discussed. Aim:To investigate the relation of gallbladder function and Hp infection to gastric mucosa inflammation in patients with symptomatic gallstones prior to cholecystectomy. Patients: Seventy-three patients with symptomatic gallstones were studied by endoscopy and Hp testing. Methods: Gastritis classification was performed according to the updated Sydney System and gallbladder function was determined by total lipid concentration of gallbladder bile collected during mainly laparoscopic cholecystectomy. Results: Fifteen patients revealed no, 39 patients mild, and 19 moderate to marked gastritis. No significant differences for bile salts, phospholipids, cholesterol, or total lipids in gallbladder bile were found between these three groups of patients. However, while only 1 out of 54 (< 2%) patients with mild or no gastritis was found histologically positive for Hp, this infection could be detected in 14 (74%) out of 19 patients with moderate to marked gastritis. Conclusion: Moderate to marked gastric mucosa inflammation in gallstone patients is mainly caused by Hp infection, whereas gallbladder function is not related to the degree of gastritis. Thus, an increased alkaline duodenogastric reflux in gallstone patients seems to be of limited pathophysiological relevance. Copyright (c) 2006 S. Karger AG, Basel
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Life in the Atacama — Year 2: Geologic reconnaissance through long-range roving and implications on the search for life
The Life in the Atacama-2004 project, which included geological, morphological, and mineralogical mapping through combined satellite, field-based, and microscopic perspectives and long-range roving, led to the localization of potential habitats
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Searching for life with rovers: exploration methods and science results from the 2004 field campaign of the “Life in the Atacama” project and applications to future Mars Missions
LITA develops and field tests a long-range automated rover and a science payload to search for microbial life in the Atacama. The Atacama's evolution provides a unique training ground for designing and testing exploration strategies and life detection methods for the search for life on Mars
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Spectroscopic results from the Life in the Atacama (LITA) project 2004 field season
Analysis of spectroscopy datasets from rover field tests in the Atacama Desert (Chile), focusing on the composition of the surface and identification of potential habitats for life
Plural valuation of nature for equity and sustainability: Insights from the Global South
Plural valuation is about eliciting the diverse values of nature articulated by different stakeholders in order to inform decision making and thus achieve more equitable and sustainable outcomes. We explore what approaches align with plural valuation on the ground, as well as how different social-ecological contexts play a role in translating plural valuation into decisions and outcomes. Based on a co-constructed analytical approach relying on empirical information from ten cases from the Global South, we find that plural valuation contributes to equitable and sustainable outcomes if the valuation process: 1) is based on participatory value elicitation approaches; 2) is framed with a clear action-oriented purpose; 3) provides space for marginalized stakeholders to articulate their values in ways that can be included in decisions; 4) is used as a tool to identify and help reconcile different cognitive models about human-nature relations; and 5) fosters open communication and collaboration among stakeholders. We also find that power asymmetries can hinder plural valuation. As interest and support for undertaking plural valuation grows, a deeper understanding is needed regarding how it can be adapted to different purposes, approaches, and social-ecological contexts in order to contribute to social equity and sustainability
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