5,606 research outputs found

    Quantizing the line element field

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    A metric with signature (-+++) can be constructed from a metric with signature (++++) and a double-sided vector field called the line element field. Some of the classical and quantum properties of this vector field are studied.Comment: 9 page

    Geochemistry of cold seeps - Fluid sources and systematics

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    Emanation of fluids at cold seeps, mud volcanoes, and other types of submarine seepage structures is a typical phenomenon occurring at continental margins worldwide. They represent pathways along which volatiles and solutes are recycled from deeply buried sediments into the global ocean, and hence they may be considered as a potentially important link in global geochemical cycles. In this contribution we present geochemical data from various geological and tectonic settings such as the Gulf of Cadiz, the convergent margin off Central America, and/or the Black Sea and provide approaches how to systemize available data sets. Clay-mineral dewatering plays a central role in terms of fluid-mobilization from greater depth, however, resulting cold seep fluids are typically very different from each other and cover a large range of geochemical signatures. This is is due to variations in control parameters such as the type and thickness of the sediment cover, thermal conditions, extension of fluid pathways, and the potential for secondary overprinting. For example, freshened fluids emanating at cold seeps off Costa Rica indicate dewatering and related geochemical reactions in subducting sediments, while fluids sampled at mud volcanoes in the Gulf of Cadiz provide evidence for a high-temperature fluid source originating in the underlying oceanic basement. The latter finding provides evidence for a hydrological connection between buried oceanic crust and the water column even at old crustal ages. Varius geochemical tracers were proposed in the past to decipher relevant processes in the subsurface. In a recent systematic study, Scholz et al. [1] demonstrated the general use of Li, reflecting the temperature-dependent isotope fractionation during early diagenetic Li uptake and burial diagenetic Li release from sediments. However, additional approaches are required in order to provide robust geochmical interpretations of cold seep fluids

    Heterogeneity in 12^{12}CO/13^{13}CO Ratios Toward Solar-Type Young Stellar Objects

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    This study reports an unusual heterogeneity in [12^{12}C16^{16}O]/[13^{13}C16^{16}O] abundance ratios of carbon monoxide observed in the gas phase toward seven ~ solar-mass YSOs and three dense foreground clouds in the nearby star-forming regions, Ophiuchus, Corona Australis, Orion, Vela and an isolated core, L43. Robust isotope ratios were derived using infrared absorption spectroscopy of the 4.7 Ī¼\mum fundamental and 2.3 Ī¼\mum overtone rovibrational bands of CO at very high resolution (Ī»\lambda/Ī”\DeltaĪ»ā‰ˆ95,000\lambda\approx 95,000), observed with the CRIRES spectrograph on the Very Large Telescope. We find [12^{12}C16^{16}O]/[13^{13}C16^{16}O] values ranging from ~ 85 to 165, significantly higher than those of the local interstellar medium (~ 65 to 69). These observations are evidence for isotopic heterogeneity in carbon reservoirs in solar-type YSO environments, and encourage the need for refined Galactic chemical evolution models to explain the 12^{12}C/13^{13}C discrepancy between the solar system and local ISM. The oxygen isotope ratios are consistent with isotopologue-specific photodissociation by CO self-shielding toward the disks, VV CrA N and HL Tau, further substantiating models predicting CO self-shielding on disk surfaces. However, we find that CO self-shielding is an unlikely general explanation for the high [12^{12}C16^{16}O]/[13^{13}C16^{16}O] ratios observed in this study. Comparison of the solid CO against gas-phase [12^{12}C16^{16}O]/[13^{13}C16^{16}O] suggests that interactions between CO ice and gas reservoirs need to be further investigated as at least a partial explanation for the unusually high [12^{12}C16^{16}O]/[13^{13}C16^{16}O] observed.Comment: 16 pages, 14 figures, 7 tables. Accepted for publication in The Astrophysical Journa

    The Basics of Biogerontology

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    Aging is an enormously complicated process. Despite a great many of theories (among them ā€œProgram Theoriesā€, ā€œCombined Theoriesā€, ā€œDamage Theoriesā€, ā€œInflamm-Agingā€, ā€œGarb-Agingā€ and the ā€œRising Deleteriomeā€), so far there is none which is able to explain this phenomenon satisfactorily and completely. A different approach to address the complexity of aging is to characterize the major ā€œHallmarks of Agingā€. These are genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, deregulated nutrient sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion and an altered intercellular communication. From research on these hallmarks, new avenues were opened on how to interfere with the aging process. Some of these possible therapeutic interventions are described here too
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