5,606 research outputs found
Quantizing the line element field
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
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 CO/CO Ratios Toward Solar-Type Young Stellar Objects
This study reports an unusual heterogeneity in
[CO]/[CO] 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 m fundamental
and 2.3 m overtone rovibrational bands of CO at very high resolution
(/), observed with the CRIRES
spectrograph on the Very Large Telescope. We find
[CO]/[CO] 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 C/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 [CO]/[CO] ratios
observed in this study. Comparison of the solid CO against gas-phase
[CO]/[CO] suggests that interactions between CO ice
and gas reservoirs need to be further investigated as at least a partial
explanation for the unusually high [CO]/[CO]
observed.Comment: 16 pages, 14 figures, 7 tables. Accepted for publication in The
Astrophysical Journa
The Basics of Biogerontology
Aging is an enormously complicated process. Despite a great many of theories (among them āProgram Theoriesā, āCombined Theoriesā, āDamage Theoriesā, āInflamm-Agingā, āGarb-Agingā and the āRising 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 āHallmarks 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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