The Permian–Triassic Boundary event at 252.2 Ma marks the largest extinction of marine fauna in the Phanerozoic and there is a wide consensus that the extinction coincided with an intense oceanic ...anoxic event. The stratotype of the Changhsingian Stage, precisely constrained by the PTB Global Stratotype Section and Point (GSSP) and the GSSP for the Wuchiapingian–Changhsingian Boundary, both at Meishan in southern China, is well-documented in respect to geochronology and the pattern of extinction. Here we report secular trends in bulk isotopic parameters and lipid biomarkers in a core spanning 214 m of stratigraphic section across the PTB and through the entire Changhsingian interval. Our analysis of these data, viewed in the context of relative sea level change and strontium isotopes, reveals distinct shifts in paleoenvironmental conditions and profound changes in plankton ecology well before and following the biological extinction event. Specifically, patterns of steroids and triterpenoids indicate a marine plankton community that was heavily dominated by bacteria during the late Wuchiapingian, middle Changhsingian and early Griesbachian stages. Secular trends in aromatic hydrocarbons diagnostic for anoxygenic green sulphur bacteria (Chlorobiaceae) identify periods when euxinic conditions extended into the photic zone during the entire Changhsingian stage. Here also, the
δ
15N of organic nitrogen progressively shifted from positive values around +
2 or +
3‰ to −
1‰ coincident with a sharp negative excursion in
δ
13C
org and slightly postdating the sharp minimum in
δ
13C values of inorganic carbon that occurs at the top of Bed 24. These results, together the published chronology indicate that conditions unfavourable for aerobiosis existed in the marine photic zone at Meishan for 1.5 million years prior to the main phase of the biological extinction. The induction of marine euxinic conditions, worldwide, at the end of the Permian was likely a consequence of the aggregation of Pangea and the uplift, weathering and transport of nutrients to the ocean well in advance of the PTB. The protracted and widespread nature of the ensuing oceanic anoxic event suggests a causal association with the mass extinction.
This review of material relevant to the Conference on Biosignature Preservation and Detection in Mars Analog Environments summarizes the meeting materials and discussions and is further expanded upon ...by detailed references to the published literature. From this diverse source material, there is a detailed discussion on the habitability and biosignature preservation potential of five primary analog environments: hydrothermal spring systems, subaqueous environments, subaerial environments, subsurface environments, and iron-rich systems. Within the context of exploring past habitable environments on Mars, challenges common to all of these key environments are laid out, followed by a focused discussion for each environment regarding challenges to orbital and ground-based observations and sample selection. This leads into a short section on how these challenges could influence our strategies and priorities for the astrobiological exploration of Mars. Finally, a listing of urgent needs and future research highlights key elements such as development of instrumentation as well as continued exploration into how Mars may have evolved differently from Earth and what that might mean for biosignature preservation and detection. Key Words: Biosignature preservation-Biosignature detection-Mars analog environments-Conference report-Astrobiological exploration. Astrobiology 17, 363-400.
Organisms require faithful DNA replication to avoid deleterious mutations. In yeast, replicative leading- and lagging-strand DNA polymerases (Pols ε and δ, respectively) have intrinsic proofreading ...exonucleases that cooperate with each other and mismatch repair to limit spontaneous mutation to less than 1 per genome per cell division. The relationship of these pathways in mammals and their functions in vivo are unknown. Here we show that mouse Pol ε and δ proofreading suppress discrete mutator and cancer phenotypes. We found that inactivation of Pol ε proofreading elevates base-substitution mutations and accelerates a unique spectrum of spontaneous cancers; the types of tumors are entirely different from those triggered by loss of Pol δ proofreading. Intercrosses of Pol ε-, Pol δ-, and mismatch repair-mutant mice show that Pol ε and δ proofreading act in parallel pathways to prevent spontaneous mutation and cancer. These findings distinguish Pol ε and δ functions in vivo and reveal tissue-specific requirements for DNA replication fidelity.
We present the result of a search of the Milagro sky map for spatial correlations with sources from a subset of the recent Fermi Bright Source List (BSL). The BSL consists of the 205 most significant ...sources detected above 100 MeV by the Fermi Large Area Telescope. We select sources based on their categorization in the BSL, taking all confirmed or possible Galactic sources in the field of view of Milagro. Of the 34 Fermi sources selected, 14 are observed by Milagro at a significance of 3 standard deviations or more. We conduct this search with a new analysis which employs newly optimized gamma-hadron separation and utilizes the full eight-year Milagro data set. Milagro is sensitive to gamma rays with energy from 1 to 100 TeV with a peak sensitivity from 10 to 50 TeV depending on the source spectrum and declination. These results extend the observation of these sources far above the Fermi energy band. With the new analysis and additional data, multi-TeV emission is definitively observed associated with the Fermi pulsar, J2229.0+6114, in the Boomerang pulsar wind nebula (PWN). Furthermore, an extended region of multi-TeV emission is associated with the Fermi pulsar, J0634.0+1745, the Geminga pulsar.
The diffuse gamma radiation arising from the interaction of cosmic-ray particles with matter and radiation in the Galaxy is one of the few probes available to study the origin of the cosmic rays. ...Data from the Milagro gamma-ray observatory--a water Cerenkov detector that continuously views 62 sr of the overhead sky--shows that the brightest extended region in the entire northern sky is the Cygnus region of the Galactic plane. The TeV image of the Cygnus region contains at least one new source, MGRO J2019+37, which is 10.9 s above the isotropic background, as well as correlations with the matter density in the region. However, the gamma-ray flux from the Cygnus region (after excluding MGRO J2019+37) as measured at 612 TeV exceeds that predicted from a model of cosmic-ray production and propagation. This observation indicates the existence of either hard-spectrum cosmic-ray sources and/or unresolved sources of TeV gamma rays in the region.
The Large Area Telescope on board the Fermi Gamma-ray Space Telescope detected a strong γ-ray flare on 2011 May 15 from a source identified as 4C +49.22, a flat spectrum radio quasar (FSRQ) also ...known as S4 1150+49. This blazar, characterized by a prominent radio–optical–X-ray jet, was in a low γ-ray activity state during the first years of Fermi observations. Simultaneous observations during the quiescent, outburst and post-flare γ-ray states were obtained by Swift, Planck and optical–IR–radio telescopes (Instituto Nacional de Astrofísica, Óptica y Electrónica, Catalina Sky Survey, Very Long Baseline Array VLBA, Metsähovi). The flare is observed from microwave to X-ray bands with correlated variability and the Fermi, Swift and Planck data for this FSRQ show some features more typical of BL Lac objects, like the synchrotron peak in the optical band that outshines the thermal blue-bump emission, and the X-ray spectral softening. Multi-epoch VLBA observations show the ejection of a new component close in time with the GeV γ-ray flare. The radio-to-γ-ray spectral energy distribution is modelled and fitted successfully for the outburst and the post-flare epochs using either a single flaring blob with two emission processes (synchrotron self-Compton (SSC), and external-radiation Compton), and a two-zone model with SSC-only mechanism.
Advancements in electrode technologies to both stimulate and record the central nervous system's electrical activities are enabling significant improvements in both the understanding and treatment of ...different neurological diseases. However, the current neural recording and stimulating electrodes are metallic, requiring invasive and damaging methods to interface with neural tissue. These electrodes may also degrade, resulting in additional invasive procedures. Furthermore, metal electrodes may cause nerve damage due to their inherent rigidity. This paper demonstrates that novel electrically conductive organic fibers (ECFs) can be used for direct nerve stimulation. The ECFs were prepared using a standard polyester material as the structural base, with a carbon nanotube ink applied to the surface as the electrical conductor. We report on three experiments: the first one to characterize the conductive properties of the ECFs; the second one to investigate the fiber cytotoxic properties in vitro; and the third one to demonstrate the utility of the ECF for direct nerve stimulation in an in vivo rodent model.
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