927 research outputs found
The Supernova Triggered Formation and Enrichment of Our Solar System
We investigate the enrichment of the pre-solar cloud core with short lived
radionuclides (SLRs), especially 26Al. The homogeneity and the surprisingly
small spread in the ratio 26Al/27Al observed in the overwhelming majority of
calcium-aluminium-rich inclusions (CAIs) in a vast variety of primitive
chondritic meteorites places strong constraints on the formation of the the
solar system. Freshly synthesized radioactive 26Al has to be included and well
mixed within 20kyr. After discussing various scenarios including X-winds, AGB
stars and Wolf-Rayet stars, we come to the conclusion that triggering the
collapse of a cold cloud core by a nearby supernova is the most promising
scenario. We then narrow down the vast parameter space by considering the
pre-explosion survivability of such a clump as well as the cross-section
necessary for sufficient enrichment. We employ numerical simulations to address
the mixing of the radioactively enriched SN gas with the pre-existing gas and
the forced collapse within 20kyr. We show that a cold clump of 10Msun at a
distance of 5pc can be sufficiently enriched in 26Al and triggered into
collapse fast enough - within 18kyr after encountering the supernova shock -
for a range of different metallicities and progenitor masses, even if the
enriched material is assumed to be distributed homogeneously in the entire
supernova bubble. In summary, we envision an environment for the birth place of
the Solar System 4.567Gyr ago similar to the situation of the pillars in M16
nowadays, where molecular cloud cores adjacent to an HII region will be hit by
a supernova explosion in the future. We show that the triggered collapse and
formation of the Solar System as well as the required enrichment with
radioactive 26Al are possible in this scenario.Comment: 12 pages, 8 figures, accepted for publication in ApJ. Resolution of
most figures degraded to fit within arXiv size limits. A full resolution
version is available at
http://www.usm.uni-muenchen.de/~gritschm/Gritschneder_2011_sun.pd
A perspective from extinct radionuclides on a Young Stellar Object: The Sun and its accretion disk
Meteorites, which are remnants of solar system formation, provide a direct
glimpse into the dynamics and evolution of a young stellar object (YSO), namely
our Sun. Much of our knowledge about the astrophysical context of the birth of
the Sun, the chronology of planetary growth from micrometer-sized dust to
terrestrial planets, and the activity of the young Sun comes from the study of
extinct radionuclides such as 26Al (t1/2 = 0.717 Myr). Here we review how the
signatures of extinct radionuclides (short-lived isotopes that were present
when the solar system formed and that have now decayed below detection level)
in planetary materials influence the current paradigm of solar system
formation. Particular attention is given to tying meteorite measurements to
remote astronomical observations of YSOs and modeling efforts. Some extinct
radionuclides were inherited from the long-term chemical evolution of the
Galaxy, others were injected into the solar system by a nearby supernova, and
some were produced by particle irradiation from the T-Tauri Sun. The chronology
inferred from extinct radionuclides reveals that dust agglomeration to form
centimeter-sized particles in the inner part of the disk was very rapid (<50
kyr), planetesimal formation started early and spanned several million years,
planetary embryos (possibly like Mars) were formed in a few million years, and
terrestrial planets (like Earth) completed their growths several tens of
million years after the birth of the Sun.Comment: 49 pages, 9 figures, 1 table. Uncorrected preprin
Mas-related G-proteinâcoupled receptors inhibit pathological pain in mice
An important objective of pain research is to identify novel drug targets for the treatment of pathological persistent pain states, such as inflammatory and neuropathic pain. Mas-related G-proteinâcoupled receptors (Mrgprs) represent a large family of orphan receptors specifically expressed in small-diameter nociceptive primary sensory neurons. To determine the roles of Mrgprs in persistent pathological pain states, we exploited a mouse line in which a chromosomal locus spanning 12 Mrgpr genes was deleted (KO). Initial studies indicated that these KO mice show prolonged mechanical- and thermal-pain hypersensitivity after hind-paw inflammation compared with wild-type littermates. Here, we show that this mutation also enhances the windup response of dorsal-horn wide dynamic-range neurons, an electrophysiological model for the triggering of central pain sensitization. Deletion of the Mrgpr cluster also blocked the analgesic effect of intrathecally applied bovine adrenal medulla peptide 8â22 (BAM 8â22), an MrgprC11 agonist, on both inflammatory heat hyperalgesia and neuropathic mechanical allodynia. Spinal application of bovine adrenal medulla peptide 8â22 also significantly attenuated windup in wild-type mice, an effect eliminated in KO mice. These data suggest that members of the Mrgpr family, in particular MrgprC11, may constitute an endogenous inhibitory mechanism for regulating persistent pain in mice. Agonists for these receptors may, therefore, represent a class of antihyperalgesics for treating persistent pain with minimal side effects because of the highly specific expression of their targets
Recollements of Module Categories
We establish a correspondence between recollements of abelian categories up
to equivalence and certain TTF-triples. For a module category we show,
moreover, a correspondence with idempotent ideals, recovering a theorem of
Jans. Furthermore, we show that a recollement whose terms are module categories
is equivalent to one induced by an idempotent element, thus answering a
question by Kuhn.Comment: Comments are welcom
The alpha 7 nicotinic receptor agonist PHA-543613 hydrochloride inhibits <i>Porphyromonas gingivalis</i>-induced expression of interleukin-8 by oral keratinocytes
Objective:
The alpha 7 nicotinic receptor (α7nAChR) is expressed by oral keratinocytes. α7nAChR activation mediates anti-inflammatory responses. The objective of this study was to determine if α7nAChR activation inhibited pathogen-induced interleukin-8 (IL-8) expression by oral keratinocytes.<p></p>
Materials and methods:
Periodontal tissue expression of α7nAChR was determined by real-time PCR. OKF6/TERT-2 oral keratinocytes were exposed to <i>Porphyromonas gingivalis</i> in the presence and absence of a α7nAChR agonist (PHA-543613 hydrochloride) alone or after pre-exposure to a specific α7nAChR antagonist (α-bungarotoxin). Interleukin-8 (IL-8) expression was measured by ELISA and real-time PCR. Phosphorylation of the NF-ÎșB p65 subunit was determined using an NF-ÎșB p65 profiler assay and STAT-3 activation by STAT-3 in-cell ELISA. The release of ACh from oral keratinocytes in response to <i>P. gingivalis</i> lipopolysaccharide was determined using a GeneBLAzer M3 CHO-K1-blacell reporter assay.<p></p>
Results:
Expression of α7nAChR mRNA was elevated in diseased periodontal tissue. PHA-543613 hydrochloride inhibited <i>P. Gingivalis</i>-induced expression of IL-8 at the transcriptional level. This effect was abolished when cells were pre-exposed to a specific α7nAChR antagonist, α-bungarotoxin. PHA-543613 hydrochloride downregulated NF-ÎșB signalling through reduced phosphorylation of the NF-ÎșB p65-subunit. In addition, PHA-543613 hydrochloride promoted STAT-3 signalling by maintenance of phosphorylation. Furthermore, oral keratinocytes upregulated ACh release in response to <i>P. Gingivalis</i> lipopolysaccharide.<p></p>
Conclusion:
These data suggest that α7nAChR plays a role in regulating the innate immune responses of oral keratinocytes.<p></p>
<i>Plasmodium falciparum </i>var genes expressed in children with severe malaria encode CIDRα1 domains
Most severe Plasmodium falciparum infections are experienced by young children. Severe symptoms are precipitated by vascular sequestration of parasites expressing a particular subset of the polymorphic P. falciparum erythrocyte membrane protein 1 (PfEMP1) adhesion molecules. Parasites binding human endothelial protein C receptor (EPCR) through the CIDRα1 domain of certain PfEMP1 were recently associated with severe malaria in children. However, it has remained unclear to which extend the EPCRâbinding CIDRα1 domains epitomize PfEMP1 expressed in severe malaria. Here, we characterized the near fullâlength transcripts dominating the var transcriptome in children with severe malaria and found that the only common feature of the encoded PfEMP1 was CIDRα1 domains. Such genes were highly and dominantly expressed in both children with severe malarial anaemia and cerebral malaria. These observations support the hypothesis that the CIDRα1âEPCR interaction is key to the pathogenesis of severe malaria and strengthen the rationale for pursuing a vaccine or adjunctive treatment aiming at inhibiting or reducing the damaging effects of this interaction
Structural correlations in heterogeneous electron transfer at monolayer and multilayer graphene electrodes
As a new form of carbon, graphene is attracting intense interest as an electrode material with widespread applications. In the present study, the heterogeneous electron transfer (ET) activity of graphene is investigated using scanning electrochemical cell microscopy (SECCM), which allows electrochemical currents to be mapped at high spatial resolution across a surface for correlation with the corresponding structure and properties of the graphene surface. We establish that the rate of heterogeneous ET at graphene increases systematically with the number of graphene layers, and show that the stacking in multilayers also has a subtle influence on ET kinetics. © 2012 American Chemical Society
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