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1011.
  • Zensus, J. A., et al. (författare)
  • The inner radio jet of 3C273
  • 1988
  • Ingår i: Nature. - London : Nature Publishing Group. - 0028-0836. ; 334:6181, s. 410-412
  • Tidskriftsartikel (refereegranskat)abstract
    • Radio maps of 3C273 obtained with very long baseline interferometry (VLBI) have been limited by low dynamic range and poor north-south resolution resulting from the low declination (2°) of this quasar1. Dramatic improvement can now be achieved using larger arrays and antennas in the Southern Hemisphere2,3. A new VLBI map, made at 5 GHz with angular resolution and dynamic range unsurpassed at this frequency for this source, shows a narrow jet extending to a projected distance lproj∼125 h-;1 parsecs from the core. Superluminal motion exists out to at least lproj≈46h-1 parsecs. Successive superluminal components emerge from the core and appear to move on a fixed curved path with similar speeds of about 1 milliarcseconds per year. © 1988 Nature Publishing Group.
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1012.
  • Zhang, R., et al. (författare)
  • Chemical mapping of a single molecule by plasmon-enhanced Raman scattering
  • 2013
  • Ingår i: Nature. - 0028-0836. ; 498:7452, s. 82-86
  • Tidskriftsartikel (refereegranskat)abstract
    • Visualizing individual molecules with chemical recognition is a longstanding target in catalysis, molecular nanotechnology and biotechnology. Molecular vibrations provide a valuable 'finger-print' for such identification. Vibrational spectroscopy based on tip-enhanced Raman scattering allows us to access the spectral signals of molecular species very efficiently via the strong localized plasmonic fields produced at the tip apex(1-11). However, the best spatial resolution of the tip-enhanced Raman scattering imaging is still limited to 3-15 nanometres(5,12-16), which is not adequate for resolving a single molecule chemically. Here we demonstrate Raman spectral imaging with spatial resolution below one nanometre, resolving the inner structure and surface configuration of a single molecule. This is achieved by spectrally matching the resonance of the nanocavity plasmon to the molecular vibronic transitions, particularly the downward transition responsible for the emission of Raman photons. This matching is made possible by the extremely precise tuning capability provided by scanning tunnelling microscopy. Experimental evidence suggests that the highly confined and broadband nature of the nanocavity plasmon field in the tunnelling gap is essential for ultrahigh-resolution imaging through the generation of an efficient double-resonance enhancement for both Raman excitation and Raman emission. Our technique not only allows for chemical imaging at the single-molecule level, but also offers a new way to study the optical processes and photochemistry of a single molecule.
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1013.
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1014.
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1015.
  • Zisoulis, Dimitrios G., et al. (författare)
  • Autoregulation of microRNA biogenesis by let-7 and Argonaute
  • 2012
  • Ingår i: Nature. - 0028-0836. ; 486:7404, s. 541-U140
  • Tidskriftsartikel (refereegranskat)abstract
    • MicroRNAs (miRNAs) comprise a large family of small RNA molecules that post-transcriptionally regulate gene expression in many biological pathways(1). Most miRNAs are derived from long primary transcripts that undergo processing by Drosha to produce similar to 65-nucleotide precursors that are then cleaved by Dicer, resulting in the mature 22-nucleotide forms(2,3). Serving as guides in Argonaute protein complexes, mature miRNAs use imperfect base pairing to recognize sequences in messenger RNA transcripts, leading to translational repression and destabilization of the target messenger RNAs4,5. Here we show that the miRNA complex also targets and regulates non-coding RNAs that serve as substrates for the miRNA-processing pathway. We found that the Argonaute protein in Caenorhabditis elegans, ALG-1, binds to a specific site at the 3' end of let-7 miRNA primary transcripts and promotes downstream processing events. This interaction is mediated by mature let-7 miRNA through a conserved complementary site in its own primary transcript, thus creating a positive-feedback loop. We further show that ALG-1 associates with let-7 primary transcripts in nuclear fractions. Argonaute also binds let-7 primary transcripts in human cells, demonstrating that the miRNA pathway targets non-coding RNAs in addition to protein-coding messenger RNAs across species. Moreover, our studies in C. elegans reveal a novel role for Argonaute in promoting biogenesis of a targeted transcript, expanding the functions of the miRNA pathway in gene regulation. This discovery of autoregulation of let-7 biogenesis establishes a new mechanism for controlling miRNA expression.
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1016.
  • Zopf, David, et al. (författare)
  • Weak-affinity Chromatography
  • 1990
  • Ingår i: Nature. - 0028-0836. ; 346, s. 87-88
  • Tidskriftsartikel (refereegranskat)abstract
    • Weak-affinity chromatography is a new method using readily reversible biospecific recognition as the basis for chromatographic separations. 
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1017.
  • Zygmunt, Peter M., et al. (författare)
  • Vanilloid receptors on sensory nerves mediate the vasodilator action of anandamide
  • 1999
  • Ingår i: Nature. - Nature Publishing Group. - 0028-0836. ; 400:6743, s. 452-457
  • Tidskriftsartikel (refereegranskat)abstract
    • The endogenous cannabinoid receptor agonist anandamide is a powerful vasodilator of isolated vascular preparations, but its mechanism of action is unclear. Here we show that the vasodilator response to anandamide in isolated arteries is capsaicin-sensitive and accompanied by release of calcitonin- gene-related peptide (CGRP). The selective CGRP-receptor antagonist 8-37 CGRP (ref. 5), but not the cannabinoid CB1 receptor blocker SR141716A (ref. 7), inhibited the vasodilator effect of anandamide. Other endogenous. (2- arachidonylglycerol, palmitylethanolamide) and synthetic (HU 210, WIN 55,212- 2, CP 55,940) CB1 and CB2 receptor agonists could not mimic the action of anandamide. The selective 'vanilloid receptor' antagonist capsazepine inhibited anandamide-induced vasodilation and release of CGRP. In patch-clamp experiments on cells expressing the cloned vanilloid receptor (VR1), anandamide induced a capsazepine-sensitive current in whole cells and isolated membrane patches. Our results indicate that anandamide induces vasodilation by activating vanilloid receptors on perivascular sensory nerves and causing release of CGRP. The vanilloid receptor may thus be another molecular target for endogenous anandamide, besides cannabinoid receptors, in the nervous and cardiovascular systems.
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1018.
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1019.
  • Cannon, Johanna, 1982-, et al. (författare)
  • Xenacoelomorpha is the sister group to Nephrozoa
  • 2016
  • Ingår i: Nature. - ISSN: 0028-0836. ; 530, s. 89-93
  • Tidskriftsartikel (refereegranskat)abstract
    • The position of Xenacoelomorpha in the tree of life remains a major unresolved question in the study of deep animal relationships1. Xenacoelomorpha, comprising Acoela, Nemertodermatida, and Xenoturbella, are bilaterally symmetrical marine worms that lack several features common to most other bilaterians, for example an anus, nephridia, and a circulatory system. Two conflicting hypotheses are under debate: Xenacoelomorpha is the sister group to all remaining Bilateria (= Nephrozoa, namely protostomes and deuterostomes)2,3 or is a clade inside Deuterostomia4. Thus, determining the phylogenetic position of this clade is pivotal for understanding the early evolution of bilaterian features, or as a case of drastic secondary loss of complexity. Here we show robust phylogenomic support for Xenacoelomorpha as the sister taxon of Nephrozoa. Our phylogenetic analyses, based on 11 novel xenacoelomorph transcriptomes and using different models of evolution under maximum likelihood and Bayesian inference analyses, strongly corroborate this result. Rigorous testing of 25 experimental data sets designed to exclude data partitions and taxa potentially prone to reconstruction biases indicates that long- branch attraction, saturation, and missing data do not influence these results. The sister group relationship between Nephrozoa and Xenacoelomorpha supported by our phylogenomic analyses implies that the last common ancestor of bilaterians was probably a benthic, ciliated acoelomate worm with a single opening into an epithelial gut, and that excretory organs, coelomic cavities, and nerve cords evolved after xenacoelomorphs separated from the stem lineage of Nephrozoa. 
1020.
  • Donoghue, Philip C. J., et al. (författare)
  • Synchrotron X-ray tomographic microscopy of fossil embryos
  • 2006
  • Ingår i: Nature. - ISSN: 0028-0836. ; 442:7103, s. 601-718
  • Tidskriftsartikel (refereegranskat)abstract
    • Fossilized embryos from the late Neoproterozoic and earliest Phanerozoic have caused much excitement because they preserve the earliest stages of embryology of animals that represent the initial diversification of metazoans1, 2, 3, 4. However, the potential of this material has not been fully realized because of reliance on traditional, non-destructive methods that allow analysis of exposed surfaces only1, 2,3, 4, and destructive methods that preserve only a single two-dimensional view of the interior of the specimen5, 6. Here, we have applied synchrotron-radiation X-ray tomographic microscopy (SRXTM)7, obtaining complete three-dimensional recordings at submicrometre resolution. The embryos are preserved by early diagenetic impregnation and encrustation with calcium phosphate, and differences in X-ray attenuation provide information about the distribution of these two diagenetic phases. Three-dimensional visualization of blastomere arrangement and diagenetic cement in cleavage embryos resolves outstanding questions about their nature, including the identity of the columnar blastomeres. The anterior and posterior anatomy of embryos of the bilaterian worm-like Markuelia confirms its position as a scalidophoran, providing new insights into body-plan assembly among constituent phyla. The structure of the developing germ band in another bilaterian, Pseudooides, indicates a unique mode of germ-band development. SRXTM provides a method of non-invasive analysis that rivals the resolution achieved even by destructive methods, probing the very limits of fossilization and providing insight into embryology during the emergence of metazoan phyla.
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