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  • 1
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    Macrofossil evidence for a rapid and severe Cretaceous–Paleogene mass extinction in Antarctica (2016)
    Springer Nature
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    Publikationsdatum: 2016-05-28
    Beschreibung: Article Debate surrounds the causes, timing, and effects of the Cretaceous-Paleogene mass extinction, 66 Ma. Here, using new collections of marine macrofossils from Seymour Island, Antarctica, the authors show that the extinction was both rapid and severe in the high southern latitudes, contrary to previous studies. Nature Communications doi: 10.1038/ncomms11738 Authors: James D. Witts, Rowan J. Whittle, Paul B. Wignall, J. Alistair Crame, Jane E. Francis, Robert J. Newton, Vanessa C. Bowman
    Digitale ISSN: 2041-1723
    Thema: Biologie , Chemie und Pharmazie , Allgemeine Naturwissenschaft , Physik
    Publiziert von Springer Nature
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  • 2
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    Paleogeographic controls on the onset of the Antarctic Circumpolar Current (2013)
    Wiley
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    Publikationsdatum: 2013-09-11
    Beschreibung: [1]  Development of the Antarctic Circumpolar Current (ACC) during the Cenozoic is controversial in terms of timing and its role in major climate transitions. Some propose that the development of the ACC was instrumental in the continental scale glaciation of Antarctica and climate cooling at the Eocene/Oligocene boundary. Here we present climate model results that show a coherent ACC was not possible during the Oligocene due to Australasian paleogeography, despite deep water connections through the Drake Passage and Tasman Gateway and the initiation of Antarctic glaciation. The simulations of ocean currents compare well to paleoenvironmental records relating to the physical oceanography of the Oligocene and provide a framework for understanding apparently contradictory dating of the initiation of the ACC. We conclude that the northward motion of the Australasian land masses and the reconfiguration of the Tasman Seaway and Drake Passage are necessary preconditions for the formation of a strong, coherent ACC.
    Print ISSN: 0094-8276
    Digitale ISSN: 1944-8007
    Thema: Geologie und Paläontologie , Physik
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
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  • 3
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    Dynamics of O(3P) + C2H4 multichannel reaction [Chemistry] (2012)
    National Academy of Sciences
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    Publikationsdatum: 2012-06-20
    Beschreibung: The O(3P) + C2H4 reaction, of importance in combustion and atmospheric chemistry, stands out as a paradigm reaction involving triplet- and singlet-state potential energy surfaces (PESs) interconnected by intersystem crossing (ISC). This reaction poses challenges for theory and experiments owing to the ruggedness and high dimensionality of these potentials, as well as the long lifetimes of the collision complexes. Primary products from five competing channels (H + CH2CHO, H + CH3CO, H2 + CH2CO, CH3 + HCO, CH2 + CH2O) and branching ratios (BRs) are determined in crossed molecular beam experiments with soft electron-ionization mass-spectrometric detection at a collision energy of 8.4 kcal/mol. As some of the observed products can only be formed via ISC from triplet to singlet PESs, from the product BRs the extent of ISC is inferred. A new full-dimensional PES for the triplet state as well as spin-orbit coupling to the singlet PES are reported, and roughly half a million surface hopping trajectories are run on the coupled singlet-triplet PESs to compare with the experimental BRs and differential cross-sections. Both theory and experiment find almost equal contributions from the two PESs to the reaction, posing the question of how important is it to consider the ISC as one of the nonadiabatic effects for this and similar systems involved in combustion chemistry. Detailed comparisons at the level of angular and translational energy distributions between theory and experiment are presented for the two primary channel products, CH3 + HCO and H + CH2CHO. The agreement between experimental and theoretical functions is excellent, implying that theory has reached the capability of describing complex multichannel nonadiabatic reactions.
    Print ISSN: 0027-8424
    Digitale ISSN: 1091-6490
    Thema: Biologie , Medizin , Allgemeine Naturwissenschaft
    Publiziert von National Academy of Sciences
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  • 4
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    Engineering behaviour and mechanical - empirical relationships for a problematic New Zealand tropical residual soil (2019)
    Geological Society of London
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    Publikationsdatum: 2019
    Beschreibung: 〈span〉〈div〉Abstract〈/div〉Unlike sedimentary clays, many residual soils do not exhibit clear mechanical-empirical relationships to assist in their engineering characterisation. In contrast, this paper discusses one residual clay in which such relationships may be determined, and examines whether the effects of structure in this clay may be assessed using a framework previously developed for sedimentary clays. The Northland Allochthon residual clay of New Zealand is a problematic soil of the fersiallitic type, prone to slope instability. Atterberg limit tests on soils from five field sites in the same geological unit show considerable variation, but that they are mechanically related. Triaxial tests were performed on reconstituted and intact soil specimens from one field site. Normalization of the strength envelope using the equivalent stress on the intrinsic compression line suggests that soil structure, destroyed in reconstituted specimens, plays a role in the shear strength of this soil in its intact state. Overconsolidated behaviour, in the absence of geological preloading, suggests the existence of a pseudo-preconsolidation pressure associated with weathering processes. The results show that the saturated mechanical behaviour of this residual soil is in line with that of sedimentary clays and that mechanical-empirical relationships developed for such clays may be applied in this case.〈/span〉
    Print ISSN: 1470-9236
    Digitale ISSN: 2041-4803
    Thema: Geologie und Paläontologie
    Publiziert von Geological Society of London
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  • 5
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    Single-channel mechanosensitive currents (1991)
    American Association for the Advancement of Science (AAAS)
    Details
    Publikationsdatum: 1991-08-16
    Beschreibung: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Sachs, F -- Sigurdson, W -- Ruknudin, A -- Bowman, C -- New York, N.Y. -- Science. 1991 Aug 16;253(5021):800-1.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17835497" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Digitale ISSN: 1095-9203
    Thema: Biologie , Chemie und Pharmazie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik
    Publiziert von American Association for the Advancement of Science (AAAS)
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  • 6
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    Complete genome sequence of Treponema pallidum, the syphilis spirochete (1998)
    American Association for the Advancement of Science (AAAS)
    Details
    Publikationsdatum: 1998-07-17
    Beschreibung: The complete genome sequence of Treponema pallidum was determined and shown to be 1,138,006 base pairs containing 1041 predicted coding sequences (open reading frames). Systems for DNA replication, transcription, translation, and repair are intact, but catabolic and biosynthetic activities are minimized. The number of identifiable transporters is small, and no phosphoenolpyruvate:phosphotransferase carbohydrate transporters were found. Potential virulence factors include a family of 12 potential membrane proteins and several putative hemolysins. Comparison of the T. pallidum genome sequence with that of another pathogenic spirochete, Borrelia burgdorferi, the agent of Lyme disease, identified unique and common genes and substantiates the considerable diversity observed among pathogenic spirochetes.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Fraser, C M -- Norris, S J -- Weinstock, G M -- White, O -- Sutton, G G -- Dodson, R -- Gwinn, M -- Hickey, E K -- Clayton, R -- Ketchum, K A -- Sodergren, E -- Hardham, J M -- McLeod, M P -- Salzberg, S -- Peterson, J -- Khalak, H -- Richardson, D -- Howell, J K -- Chidambaram, M -- Utterback, T -- McDonald, L -- Artiach, P -- Bowman, C -- Cotton, M D -- Fujii, C -- Garland, S -- Hatch, B -- Horst, K -- Roberts, K -- Sandusky, M -- Weidman, J -- Smith, H O -- Venter, J C -- AI31068/AI/NIAID NIH HHS/ -- New York, N.Y. -- Science. 1998 Jul 17;281(5375):375-88.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Institute for Genomic Research, Rockville, MD 20850, USA. tpdb@tigr.org〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/9665876" target="_blank"〉PubMed〈/a〉
    Schlagwort(e): Bacterial Proteins/genetics/metabolism ; Base Sequence ; Borrelia burgdorferi Group/genetics ; Carrier Proteins/genetics/metabolism ; DNA Repair/genetics ; DNA Replication/genetics ; DNA Restriction Enzymes/genetics ; Energy Metabolism/genetics ; Genes, Bacterial ; Genes, Regulator ; *Genome, Bacterial ; Heat-Shock Response/genetics ; Lipoproteins/genetics ; Membrane Proteins/genetics ; Molecular Sequence Data ; Movement ; Open Reading Frames ; Oxygen Consumption/genetics ; Protein Biosynthesis ; Recombination, Genetic ; Replication Origin ; *Sequence Analysis, DNA ; Transcription, Genetic ; Treponema pallidum/*genetics/metabolism/pathogenicity
    Print ISSN: 0036-8075
    Digitale ISSN: 1095-9203
    Thema: Biologie , Chemie und Pharmazie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik
    Publiziert von American Association for the Advancement of Science (AAAS)
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  • 7
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    Multiple prebiotic metals mediate translation [Earth, Atmospheric, and Planetary Sciences] (2018)
    National Academy of Sciences
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    Publikationsdatum: 2018-11-28
    Beschreibung: Today, Mg2+ is an essential cofactor with diverse structural and functional roles in life’s oldest macromolecular machine, the translation system. We tested whether ancient Earth conditions (low O2, high Fe2+, and high Mn2+) can revert the ribosome to a functional ancestral state. First, SHAPE (selective 2′-hydroxyl acylation analyzed by primer...
    Print ISSN: 0027-8424
    Digitale ISSN: 1091-6490
    Thema: Biologie , Medizin , Allgemeine Naturwissenschaft
    Publiziert von National Academy of Sciences
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  • 8
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    A high C/O ratio and weak thermal inversion in the atmosphere of exoplanet WASP-12b (2010)
    Nature Publishing Group (NPG)
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    Publikationsdatum: 2010-12-15
    Beschreibung: The carbon-to-oxygen ratio (C/O) in a planet provides critical information about its primordial origins and subsequent evolution. A primordial C/O greater than 0.8 causes a carbide-dominated interior, as opposed to the silicate-dominated composition found on Earth; the atmosphere can also differ from those in the Solar System. The solar C/O is 0.54 (ref. 3). Here we report an analysis of dayside multi-wavelength photometry of the transiting hot-Jupiter WASP-12b (ref. 6) that reveals C/O 〉/= 1 in its atmosphere. The atmosphere is abundant in CO. It is depleted in water vapour and enhanced in methane, each by more than two orders of magnitude compared to a solar-abundance chemical-equilibrium model at the expected temperatures. We also find that the extremely irradiated atmosphere (T 〉 2,500 K) of WASP-12b lacks a prominent thermal inversion (or stratosphere) and has very efficient day-night energy circulation. The absence of a strong thermal inversion is in stark contrast to theoretical predictions for the most highly irradiated hot-Jupiter atmospheres.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Madhusudhan, Nikku -- Harrington, Joseph -- Stevenson, Kevin B -- Nymeyer, Sarah -- Campo, Christopher J -- Wheatley, Peter J -- Deming, Drake -- Blecic, Jasmina -- Hardy, Ryan A -- Lust, Nate B -- Anderson, David R -- Collier-Cameron, Andrew -- Britt, Christopher B T -- Bowman, William C -- Hebb, Leslie -- Hellier, Coel -- Maxted, Pierre F L -- Pollacco, Don -- West, Richard G -- England -- Nature. 2011 Jan 6;469(7328):64-7. doi: 10.1038/nature09602. Epub 2010 Dec 8.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA. nmadhu@mit.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21150901" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0028-0836
    Digitale ISSN: 1476-4687
    Thema: Biologie , Chemie und Pharmazie , Medizin , Allgemeine Naturwissenschaft , Physik
    Publiziert von Nature Publishing Group (NPG)
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  • 9
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    Possible thermochemical disequilibrium in the atmosphere of the exoplanet GJ 436b (2010)
    Nature Publishing Group (NPG)
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    Publikationsdatum: 2010-04-24
    Beschreibung: The nearby extrasolar planet GJ 436b-which has been labelled as a 'hot Neptune'-reveals itself by the dimming of light as it crosses in front of and behind its parent star as seen from Earth. Respectively known as the primary transit and secondary eclipse, the former constrains the planet's radius and mass, and the latter constrains the planet's temperature and, with measurements at multiple wavelengths, its atmospheric composition. Previous work using transmission spectroscopy failed to detect the 1.4-mum water vapour band, leaving the planet's atmospheric composition poorly constrained. Here we report the detection of planetary thermal emission from the dayside of GJ 436b at multiple infrared wavelengths during the secondary eclipse. The best-fit compositional models contain a high CO abundance and a substantial methane (CH(4)) deficiency relative to thermochemical equilibrium models for the predicted hydrogen-dominated atmosphere. Moreover, we report the presence of some H(2)O and traces of CO(2). Because CH(4) is expected to be the dominant carbon-bearing species, disequilibrium processes such as vertical mixing and polymerization of methane into substances such as ethylene may be required to explain the hot Neptune's small CH(4)-to-CO ratio, which is at least 10(5) times smaller than predicted.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Stevenson, Kevin B -- Harrington, Joseph -- Nymeyer, Sarah -- Madhusudhan, Nikku -- Seager, Sara -- Bowman, William C -- Hardy, Ryan A -- Deming, Drake -- Rauscher, Emily -- Lust, Nate B -- England -- Nature. 2010 Apr 22;464(7292):1161-4. doi: 10.1038/nature09013.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Planetary Sciences Group, Department of Physics, University of Central Florida, Orlando, Florida 32816, USA. kevin218@knights.ucf.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20414304" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0028-0836
    Digitale ISSN: 1476-4687
    Thema: Biologie , Chemie und Pharmazie , Medizin , Allgemeine Naturwissenschaft , Physik
    Publiziert von Nature Publishing Group (NPG)
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  • 10
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    Small-molecule ligands bind to a distinct pocket in Ras and inhibit SOS-mediated nucleotide exchange activity [Biophysics and Computational Biology] (2012)
    National Academy of Sciences
    Details
    Publikationsdatum: 2012-04-04
    Beschreibung: The Ras gene is frequently mutated in cancer, and mutant Ras drives tumorigenesis. Although Ras is a central oncogene, small molecules that bind to Ras in a well-defined manner and exert inhibitory effects have not been uncovered to date. Through an NMR-based fragment screen, we identified a group of small molecules that all bind to a common site on Ras. High-resolution cocrystal structures delineated a unique ligand-binding pocket on the Ras protein that is adjacent to the switch I/II regions and can be expanded upon compound binding. Structure analysis predicts that compound-binding interferes with the Ras/SOS interactions. Indeed, selected compounds inhibit SOS-mediated nucleotide exchange and prevent Ras activation by blocking the formation of intermediates of the exchange reaction. The discovery of a small-molecule binding pocket on Ras with functional significance provides a new direction in the search of therapeutically effective inhibitors of the Ras oncoprotein.
    Print ISSN: 0027-8424
    Digitale ISSN: 1091-6490
    Thema: Biologie , Medizin , Allgemeine Naturwissenschaft
    Publiziert von National Academy of Sciences
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