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  • 1
    Publication Date: 2016-07-31
    Description: During the Paleocene-Eocene Thermal Maximum (PETM), the carbon isotopic signature (δ 13 C) of surface carbon-bearing phases decreased abruptly by at least 2.5 to 3.0 ‰. This carbon isotope excursion (CIE) has been attributed to widespread methane hydrate dissociation in response to rapid ocean warming. We ran a thermohydraulic modeling code to simulate hydrate dissociation due to ocean warming for various PETM scenarios. Our results show that hydrate dissociation in response to such warming can be rapid but suggest that methane release to the ocean is modest and delayed by hundreds to thousands of years after the onset of dissociation, limiting the potential for positive feedback from emissions-induced warming. In all of our simulations at least half of the dissociated hydrate methane remains beneath the seabed, suggesting that the pre-PETM hydrate inventory needed to account for all of the CIE is at least double that required for isotopic mass balance.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
    Publication Date: 2011-04-27
    Description: Using a diverse collection of small molecules we recently found that compound sets from different sources (commercial; academic; natural) have different protein-binding behaviors, and these behaviors correlate with trends in stereochemical complexity for these compound sets. These results lend insight into structural features that synthetic chemists might target when synthesizing screening collections for biological discovery. We report extensive characterization of structural properties and diversity of biological performance for these compounds and expand comparative analyses to include physicochemical properties and three-dimensional shapes of predicted conformers. The results highlight additional similarities and differences between the sets, but also the dependence of such comparisons on the choice of molecular descriptors. Using a protein-binding dataset, we introduce an information-theoretic measure to assess diversity of performance with a constraint on specificity. Rather than relying on finding individual active compounds, this measure allows rational judgment of compound subsets as groups. We also apply this measure to publicly available data from ChemBank for the same compound sets across a diverse group of functional assays. We find that performance diversity of compound sets is relatively stable across a range of property values as judged by this measure, both in protein-binding studies and functional assays. Because building screening collections with improved performance depends on efficient use of synthetic organic chemistry resources, these studies illustrate an important quantitative framework to help prioritize choices made in building such collections.
    Keywords: Organic Synthesis Toward Small-Molecule Probes and Drugs Special Feature
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
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  • 3
    Publication Date: 2012-03-27
    Description: Author(s): K. Quinn, L. Romagnani, B. Ramakrishna, G. Sarri, M. E. Dieckmann, P. A. Wilson, J. Fuchs, L. Lancia, A. Pipahl, T. Toncian, O. Willi, R. J. Clarke, M. Notley, A. Macchi, and M. Borghesi The development of current instabilities behind the front of a cylindrically expanding plasma has been investigated experimentally via proton probing techniques. A multitude of tubelike filamentary structures is observed to form behind the front of a plasma created by irradiating solid-density wire ... [Phys. Rev. Lett. 108, 135001] Published Mon Mar 26, 2012
    Keywords: Plasma and Beam Physics
    Print ISSN: 0031-9007
    Electronic ISSN: 1079-7114
    Topics: Physics
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  • 4
    Publication Date: 2013-11-30
    Description: We present Hubble Space Telescope ( HST ) optical transmission spectra of the transiting hot-Jupiter WASP-12b, taken with the Space Telescope Imaging Spectrograph instrument. The resulting spectra cover the range 2900–10 300 Swhich we combined with archival Wide Field Camera 3 spectra and Spitzer photometry to cover the full optical to infrared wavelength regions. With high spatial resolution, we are able to resolve WASP-12A's stellar companion in both our images and spectra, revealing that the companion is in fact a close binary M0V pair, with the three stars forming a triple-star configuration. We derive refined physical parameters of the WASP-12 system, including the orbital ephemeris, finding the exoplanet's density is ~20 per cent lower than previously estimated. From the transmission spectra, we are able to decisively rule out prominent absorption by TiO in the exoplanet's atmosphere, as there are no signs of the molecule's characteristic broad features nor individual bandheads. Strong pressure-broadened Na and K absorption signatures are also excluded, as are significant metal-hydride features. We compare our combined broad-band spectrum to a wide variety of existing aerosol-free atmospheric models, though none are satisfactory fits. However, we do find that the full transmission spectrum can be described by models which include significant opacity from aerosols: including Rayleigh scattering, Mie scattering, tholin haze and settling dust profiles. The transmission spectrum follows an effective extinction cross-section with a power law of index α, with the slope of the transmission spectrum constraining the quantity α T  = –3528 ± 660 K, where T is the atmospheric temperature. Rayleigh scattering (α = –4) is among the best-fitting models, though requires low terminator temperatures near 900 K. Sub-micron size aerosol particles can provide equally good fits to the entire transmission spectrum for a wide range of temperatures, and we explore corundum as a plausible dust aerosol. The presence of atmospheric aerosols also helps to explain the modestly bright albedo implied by Spitzer observations, as well as the near blackbody nature of the emission spectrum. Ti-bearing condensates on the cooler night-side is the most natural explanation for the overall lack of TiO signatures in WASP-12b, indicating the day/night cold trap is an important effect for very hot Jupiters. These findings indicate that aerosols can play a significant atmospheric role for the entire wide range of hot-Jupiter atmospheres, potentially affecting their overall spectrum and energy balance.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
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  • 5
    Publication Date: 2000-01-15
    Description: A deep-sea temperature record for the past 50 million years has been produced from the magnesium/calcium ratio (Mg/Ca) in benthic foraminiferal calcite. The record is strikingly similar in form to the corresponding benthic oxygen isotope (delta(18)O) record and defines an overall cooling of about 12 degrees C in the deep oceans with four main cooling periods. Used in conjunction with the benthic delta(18)O record, the magnesium temperature record indicates that the first major accumulation of Antarctic ice occurred rapidly in the earliest Oligocene (34 million years ago) and was not accompanied by a decrease in deep-sea temperatures.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Lear -- Elderfield -- Wilson -- New York, N.Y. -- Science. 2000 Jan 14;287(5451):269-72.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/10634774" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 6
    Publication Date: 2008-04-25
    Description: One of the most dramatic perturbations to the Earth system during the past 100 million years was the rapid onset of Antarctic glaciation near the Eocene/Oligocene epoch boundary (approximately 34 million years ago). This climate transition was accompanied by a deepening of the calcite compensation depth--the ocean depth at which the rate of calcium carbonate input from surface waters equals the rate of dissolution. Changes in the global carbon cycle, rather than changes in continental configuration, have recently been proposed as the most likely root cause of Antarctic glaciation, but the mechanism linking glaciation to the deepening of calcite compensation depth remains unclear. Here we use a global biogeochemical box model to test competing hypotheses put forward to explain the Eocene/Oligocene transition. We find that, of the candidate hypotheses, only shelf to deep sea carbonate partitioning is capable of explaining the observed changes in both carbon isotope composition and calcium carbonate accumulation at the sea floor. In our simulations, glacioeustatic sea-level fall associated with the growth of Antarctic ice sheets permanently reduces global calcium carbonate accumulation on the continental shelves, leading to an increase in pelagic burial via permanent deepening of the calcite compensation depth. At the same time, fresh limestones are exposed to erosion, thus temporarily increasing global river inputs of dissolved carbonate and increasing seawater delta13C. Our work sheds new light on the mechanisms linking glaciation and ocean acidity change across arguably the most important climate transition of the Cenozoic era.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Merico, Agostino -- Tyrrell, Toby -- Wilson, Paul A -- England -- Nature. 2008 Apr 24;452(7190):979-82. doi: 10.1038/nature06853.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉National Oceanography Centre, Southampton, European Way, Southampton SO14 3ZH, UK. agostino.merico@gkss.de〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/18432242" target="_blank"〉PubMed〈/a〉
    Keywords: Acids/analysis ; Antarctic Regions ; Atmosphere/chemistry ; Calcium Carbonate/analysis/metabolism ; Carbon/analysis/metabolism ; Carbon Isotopes ; Diatoms/metabolism ; Geologic Sediments/chemistry ; History, Ancient ; Hydrogen-Ion Concentration ; *Ice Cover ; Models, Biological ; Oceans and Seas ; Phytoplankton/metabolism ; Seawater/*analysis/*chemistry ; Time Factors
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 7
    Publication Date: 2008-10-04
    Description: The long-standing view of Earth's Cenozoic glacial history calls for the first continental-scale glaciation of Antarctica in the earliest Oligocene epoch ( approximately 33.6 million years ago), followed by the onset of northern-hemispheric glacial cycles in the late Pliocene epoch, about 31 million years later. The pivotal early Oligocene event is characterized by a rapid shift of 1.5 parts per thousand in deep-sea benthic oxygen-isotope values (Oi-1) within a few hundred thousand years, reflecting a combination of terrestrial ice growth and deep-sea cooling. The apparent absence of contemporaneous cooling in deep-sea Mg/Ca records, however, has been argued to reflect the growth of more ice than can be accommodated on Antarctica; this, combined with new evidence of continental cooling and ice-rafted debris in the Northern Hemisphere during this period, raises the possibility that Oi-1 represents a precursory bipolar glaciation. Here we test this hypothesis using an isotope-capable global climate/ice-sheet model that accommodates both the long-term decline of Cenozoic atmospheric CO(2) levels and the effects of orbital forcing. We show that the CO(2) threshold below which glaciation occurs in the Northern Hemisphere ( approximately 280 p.p.m.v.) is much lower than that for Antarctica ( approximately 750 p.p.m.v.). Therefore, the growth of ice sheets in the Northern Hemisphere immediately following Antarctic glaciation would have required rapid CO(2) drawdown within the Oi-1 timeframe, to levels lower than those estimated by geochemical proxies and carbon-cycle models. Instead of bipolar glaciation, we find that Oi-1 is best explained by Antarctic glaciation alone, combined with deep-sea cooling of up to 4 degrees C and Antarctic ice that is less isotopically depleted (-30 to -35 per thousand) than previously suggested. Proxy CO(2) estimates remain above our model's northern-hemispheric glaciation threshold of approximately 280 p.p.m.v. until approximately 25 Myr ago, but have been near or below that level ever since. This implies that episodic northern-hemispheric ice sheets have been possible some 20 million years earlier than currently assumed (although still much later than Oi-1) and could explain some of the variability in Miocene sea-level records.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Deconto, Robert M -- Pollard, David -- Wilson, Paul A -- Palike, Heiko -- Lear, Caroline H -- Pagani, Mark -- England -- Nature. 2008 Oct 2;455(7213):652-6. doi: 10.1038/nature07337.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Geosciences, University of Massachusetts, Amherst, Massachusetts 01003, USA. deconto@geo.umass.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/18833277" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Antarctic Regions ; Atmosphere/*chemistry ; Calcium ; Carbon Dioxide/*analysis ; *Cold Climate ; Greenhouse Effect ; History, 21st Century ; History, Ancient ; *Ice Cover ; Magnesium ; Oxygen Isotopes ; Seasons
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 8
    Publication Date: 2006-12-23
    Description: A 13-million-year continuous record of Oligocene climate from the equatorial Pacific reveals a pronounced "heartbeat" in the global carbon cycle and periodicity of glaciations. This heartbeat consists of 405,000-, 127,000-, and 96,000-year eccentricity cycles and 1.2-million-year obliquity cycles in periodically recurring glacial and carbon cycle events. That climate system response to intricate orbital variations suggests a fundamental interaction of the carbon cycle, solar forcing, and glacial events. Box modeling shows that the interaction of the carbon cycle and solar forcing modulates deep ocean acidity as well as the production and burial of global biomass. The pronounced 405,000-year eccentricity cycle is amplified by the long residence time of carbon in the oceans.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Palike, Heiko -- Norris, Richard D -- Herrle, Jens O -- Wilson, Paul A -- Coxall, Helen K -- Lear, Caroline H -- Shackleton, Nicholas J -- Tripati, Aradhna K -- Wade, Bridget S -- New York, N.Y. -- Science. 2006 Dec 22;314(5807):1894-8.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉National Oceanography Centre, Southampton, School of Ocean and Earth Science, European Way, Southampton SO14 3ZH, UK. H.Palike@soton.ac.uk〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17185595" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Biomass ; Calcium Carbonate/analysis ; *Carbon ; Carbon Isotopes/analysis ; *Climate ; Geologic Sediments/chemistry ; *Ice Cover ; Oxygen Isotopes/analysis ; Pacific Ocean ; Plankton ; Sunlight ; Time
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 9
    Publication Date: 2007-10-13
    Description: Human cancer is caused by the accumulation of mutations in oncogenes and tumor suppressor genes. To catalog the genetic changes that occur during tumorigenesis, we isolated DNA from 11 breast and 11 colorectal tumors and determined the sequences of the genes in the Reference Sequence database in these samples. Based on analysis of exons representing 20,857 transcripts from 18,191 genes, we conclude that the genomic landscapes of breast and colorectal cancers are composed of a handful of commonly mutated gene "mountains" and a much larger number of gene "hills" that are mutated at low frequency. We describe statistical and bioinformatic tools that may help identify mutations with a role in tumorigenesis. These results have implications for understanding the nature and heterogeneity of human cancers and for using personal genomics for tumor diagnosis and therapy.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Wood, Laura D -- Parsons, D Williams -- Jones, Sian -- Lin, Jimmy -- Sjoblom, Tobias -- Leary, Rebecca J -- Shen, Dong -- Boca, Simina M -- Barber, Thomas -- Ptak, Janine -- Silliman, Natalie -- Szabo, Steve -- Dezso, Zoltan -- Ustyanksky, Vadim -- Nikolskaya, Tatiana -- Nikolsky, Yuri -- Karchin, Rachel -- Wilson, Paul A -- Kaminker, Joshua S -- Zhang, Zemin -- Croshaw, Randal -- Willis, Joseph -- Dawson, Dawn -- Shipitsin, Michail -- Willson, James K V -- Sukumar, Saraswati -- Polyak, Kornelia -- Park, Ben Ho -- Pethiyagoda, Charit L -- Pant, P V Krishna -- Ballinger, Dennis G -- Sparks, Andrew B -- Hartigan, James -- Smith, Douglas R -- Suh, Erick -- Papadopoulos, Nickolas -- Buckhaults, Phillip -- Markowitz, Sanford D -- Parmigiani, Giovanni -- Kinzler, Kenneth W -- Velculescu, Victor E -- Vogelstein, Bert -- CA 43460/CA/NCI NIH HHS/ -- CA 57345/CA/NCI NIH HHS/ -- CA109274/CA/NCI NIH HHS/ -- CA112828/CA/NCI NIH HHS/ -- CA121113/CA/NCI NIH HHS/ -- CA62924/CA/NCI NIH HHS/ -- GM070219/GM/NIGMS NIH HHS/ -- GM07309/GM/NIGMS NIH HHS/ -- P30-CA43703/CA/NCI NIH HHS/ -- RR017698/RR/NCRR NIH HHS/ -- New York, N.Y. -- Science. 2007 Nov 16;318(5853):1108-13. Epub 2007 Oct 11.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Ludwig Center for Cancer Genetics and Therapeutics and Howard Hughes Medical Institute at Johns Hopkins Kimmel Cancer Center, Baltimore, MD 21231, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17932254" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Breast Neoplasms/*genetics/metabolism ; Cell Line ; Chromosome Mapping ; Colorectal Neoplasms/*genetics/metabolism ; Computational Biology ; DNA, Neoplasm ; Databases, Genetic ; Genes, Neoplasm ; Genome, Human ; Humans ; Metabolic Networks and Pathways/genetics ; Mice ; Mutation ; Neoplasm Proteins/genetics/metabolism ; Sequence Analysis, DNA
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 10
    Publication Date: 2011-03-18
    Description: 'Hyperthermals' are intervals of rapid, pronounced global warming known from six episodes within the Palaeocene and Eocene epochs ( approximately 65-34 million years (Myr) ago). The most extreme hyperthermal was the approximately 170 thousand year (kyr) interval of 5-7 degrees C global warming during the Palaeocene-Eocene Thermal Maximum (PETM, 56 Myr ago). The PETM is widely attributed to massive release of greenhouse gases from buried sedimentary carbon reservoirs, and other, comparatively modest, hyperthermals have also been linked to the release of sedimentary carbon. Here we show, using new 2.4-Myr-long Eocene deep ocean records, that the comparatively modest hyperthermals are much more numerous than previously documented, paced by the eccentricity of Earth's orbit and have shorter durations ( approximately 40 kyr) and more rapid recovery phases than the PETM. These findings point to the operation of fundamentally different forcing and feedback mechanisms than for the PETM, involving redistribution of carbon among Earth's readily exchangeable surface reservoirs rather than carbon exhumation from, and subsequent burial back into, the sedimentary reservoir. Specifically, we interpret our records to indicate repeated, large-scale releases of dissolved organic carbon (at least 1,600 gigatonnes) from the ocean by ventilation (strengthened oxidation) of the ocean interior. The rapid recovery of the carbon cycle following each Eocene hyperthermal strongly suggests that carbon was re-sequestered by the ocean, rather than the much slower process of silicate rock weathering proposed for the PETM. Our findings suggest that these pronounced climate warming events were driven not by repeated releases of carbon from buried sedimentary sources, but, rather, by patterns of surficial carbon redistribution familiar from younger intervals of Earth history.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Sexton, Philip F -- Norris, Richard D -- Wilson, Paul A -- Palike, Heiko -- Westerhold, Thomas -- Rohl, Ursula -- Bolton, Clara T -- Gibbs, Samantha -- England -- Nature. 2011 Mar 17;471(7338):349-52. doi: 10.1038/nature09826.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California 92093, USA. P.F.Sexton@open.ac.uk〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21412336" target="_blank"〉PubMed〈/a〉
    Keywords: Atlantic Ocean ; Atmosphere/*chemistry ; *Carbon Cycle ; Foraminifera/metabolism ; Geologic Sediments/chemistry ; Global Warming/*history ; History, Ancient ; Oceans and Seas ; Seawater/*chemistry ; Temperature
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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