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  • Periodicals Archive Online (PAO)  (162)
  • Cambridge University Press
  • Macmillian Magazines Ltd.
  • 1
    Electronic Resource
    Electronic Resource
    Discovery of a massive equatorial torus in the η Carinae stellar system (1999)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 402 (1999), S. 502-504 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The enigmatic object η Carinae is believed to represent an important, but short-lived, unstable phase in the life of the most massive stars, occurring shortly before they explode as supernovae or collapse directly to black holes. The putative binary system believed to constitute η ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/990048
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Ultrafast precessional magnetization reversal by picosecond magnetic field pulse shaping (2002)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 418 (2002), S. 509-512 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Since the invention of the first magnetic memory disk in 1954, much effort has been put into enhancing the speed, bit density and reliability of magnetic memory devices. In the case of magnetic random access memory (MRAM) devices, fast coherent magnetization rotation by precession of the entire ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature00905
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  • 3
    Electronic Resource
    Electronic Resource
    The building blocks of planets within the ‘terrestrial’ region of protoplanetary disks (2004)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 432 (2004), S. 479-482 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Our Solar System was formed from a cloud of gas and dust. Most of the dust mass is contained in amorphous silicates, yet crystalline silicates are abundant throughout the Solar System, reflecting the thermal and chemical alteration of solids during planet formation. (Even primitive bodies such ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature03088
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  • 4
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    Initial Results of an Intercomparison of AMS-Based Atmospheric 14CO2 Measurements (2013)
    Cambridge University Press
    Details
    Publication Date: 2013-01-01
    Description: This article presents results from the first 3 rounds of an international intercomparison of measurements of Δ14CO2 in liter-scale samples of whole air by groups using accelerator mass spectrometry (AMS). The ultimate goal of the intercomparison is to allow the merging of Δ14CO2 data from different groups, with the confidence that differences in the data are geophysical gradients and not artifacts of calibration. Eight groups have participated in at least 1 round of the intercomparison, which has so far included 3 rounds of air distribution between 2007 and 2010. The comparison is intended to be ongoing, so that: a) the community obtains a regular assessment of differences between laboratories; and b) individual laboratories can begin to assess the long-term repeatability of their measurements of the same source air. Air used in the intercomparison was compressed into 2 high-pressure cylinders in 2005 and 2006 at Niwot Ridge, Colorado (USA), with one of the tanks “spiked” with fossil CO2, so that the 2 tanks span the range of Δ14CO2 typically encountered when measuring air from both remote background locations and polluted urban ones. Three groups show interlaboratory comparability within l% for ambient level Δ14CO2. For high CO2/low Δ14CO2 air, 4 laboratories showed comparability within 2%. This approaches the goals set out by the World Meteorological Organization (WMO) CO2 Measurements Experts Group in 2005. One important observation is that single-sample precisions typically reported by the AMS community cannot always explain the observed differences within and between laboratories. This emphasizes the need to use long-term repeatability as a metric for measurement precision, especially in the context of long-term atmospheric monitoring.
    Print ISSN: 0033-8222
    Electronic ISSN: 1945-5755
    Topics: Archaeology , Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Published by Cambridge University Press
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  • 5
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    The Effects of Possible Contamination on the Radiocarbon Dating of the Dead Sea Scrolls II: Empirical Methods to Remove Castor Oil and Suggestions for Redating (2009)
    Cambridge University Press
    Details
    Publication Date: 2009-01-01
    Description: While kept at the Rockefeller Museum in East Jerusalem, many Dead Sea Scroll fragments were exposed to castor oil by the original team of editors in the course of cleaning the parchments. Castor oil must be regarded as a serious contaminant in relation to radiocarbon dating. If modern castor oil is present and is not removed prior to dating, the 14C dates will be skewed artificially towards modern values. In Rasmussen et al. (2001), it was shown that the standard AAA pretreatment procedure used in the 2 previous studies dating Dead Sea Scroll samples (Bonani et al. 1992; Jull et al. 1995) is not capable of removing castor oil from parchment samples. In the present work, we show that it is unlikely that castor oil reacts with the amino acids of the parchment proteins, a finding which leaves open the possibility of devising a cleaning method that can effectively remove castor oil. We then present 3 different pretreatment protocols designed to effectively remove castor oil from parchment samples. These involve 3 different cleaning techniques: extraction with supercritical CO2, ultrasound cleaning, and Soxhlet extraction—each with their own advantages and disadvantages. Our data show that the protocol involving Soxhlet extraction is the best suited for the purpose of decontaminating the Dead Sea Scrolls, and we recommend that this protocol be used in further attempts to 14C date the Dead Sea Scrolls. If such an attempt is decided on by the proper authorities, we propose a list of Scroll texts, which we suggest be redated in order to validate the 14C dates done earlier by Bonani et al. (1992) and Jull et al. (1995).
    Print ISSN: 0033-8222
    Electronic ISSN: 1945-5755
    Topics: Archaeology , Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Published by Cambridge University Press
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  • 6
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    Contamination on AMS Sample Targets by Modern Carbon is Inevitable (2016)
    Cambridge University Press
    Details
    Publication Date: 2016-02-17
    Description: Accelerator mass spectrometry (AMS) measurements of the radiocarbon content in very old samples are often challenging and carry large relative uncertainties due to possible contaminations acquired during the preparation and storage steps. In case of such old samples, the natural surrounding levels of 14C from gases in the atmosphere, which may well be the source of contamination among others, are 2–3 orders of magnitude higher than the samples themselves. Hence, serious efforts are taken during the preparation steps to have the samples pristine until measurements are performed. As samples often have to be temporarily stored until AMS measurements can be performed, storage conditions also become extremely crucial. Here we describe an assessment of this process of contamination in background AMS samples. Samples, both as pressed graphite (on AMS targets) and graphite powder, were stored in various storage conditions (CO2-spiked air) to investigate the extent of contamination. The experiments clearly show that the pressed targets are more vulnerable to contamination than the unpressed graphite. Experiments conducted with enriched CO2-spiked laboratory air also reveal that the contaminating carbon is not only limited to the target surface but also penetrates into the matrix. A combination of measurements on understanding the chemical nature of the graphitization product, combined with long-available knowledge on “adventitious carbon” from the surface science community, brought us to the conclusion that contamination is to a certain extent inevitable. However, it can be minimized, and should be dealt with by sputter-cleaning the samples individually before the actual measurement.
    Print ISSN: 0033-8222
    Electronic ISSN: 1945-5755
    Topics: Archaeology , Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Published by Cambridge University Press
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  • 7
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    The drag on needles moving in a Langmuir monolayer (2004)
    Cambridge University Press
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    Publication Date: 2004-01-10
    Description: The motion of membrane-bound objects is important in many aspects of biology and surface chemistry. Here we derive some general relations for objects moving in a surface film overlying a fluid of depth H. A solution to the problem of the drag can be obtained from a two-dimensional system of integral equations. Here we focus on the problem of an ideal needle moving edge-on (in the direction of its tip) or broadside-on (perpendicular to the direction of the tip). It is shown that in comparison to the drag on a circular disk a new scaling regime of the drag on a needle arises when the ratio between surface shear viscosity and subphase viscosity ηs/η is smaller than the length of the needle.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 8
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    The viscous drag of spheres and filaments moving in membranes or monolayers (2006)
    Cambridge University Press
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    Publication Date: 2006-07-01
    Description: We numerically calculate the drag on a sphere or a filament immersed in an incompressible viscous monolayer or membrane on one, or between two, viscous infinitely deep bulk phases. We show that contributions due to the Marangoni effect of the monolayer or membrane account for a significant part of the total drag. Effects of protrusion of objects into the three-dimensional fluids adjacent to the monolayer and membrane are investigated. Known analytical expressions in the limit of a very viscous membrane or monolayer are recovered by our numerics. A sphere in a membrane exhibits maximal drag when symmetrically immersed with the equator coinciding with the membrane plane. No discontinuity of the drag arises when the sphere is totally immersed into the subphase and detaches from the monolayer. Effects of protrusion are more important for objects moving in a membrane or monolayer of low surface viscosity. At large surface shear viscosity protrusions must be larger than the length defined by the ratio of surface to bulk viscosities to alter the drag on the object. Our calculations may be useful for the measurement of hydrodynamic radii of lipid rafts in membranes and for electrocapillary effects of spheres immersed in a surface. © 2006 Cambridge University Press.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 9
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    Complete adiabatic evaporation of highly superheated liquid jets (1992)
    Cambridge University Press
    Details
    Publication Date: 1992-03-01
    Description: A nozzle expansion into a vacuum chamber was used to investigate the evaporation of highly superheated liquid jets. The large molar specific heat of fluids with high molecular complexity — in this case C6F14 — is responsible for the new phenomena reported here. A model was developed to describe the basic physical effects. A cubic equation of state was used to describe the thermodynamic properties of the fluid. The evaporation was modelled as a sonic deflagration followed by an axisymmetric supersonic expansion. As in the case of hypersonic gas jets the final state is reached by a normal shock. For sufficiently high temperatures and expansion ratios a complete adiabatic evaporation of the liquid was found. At even higher temperatures the liquid evaporates completely within a rarefaction discontinuity. The predictions of the model are in good agreement with the experimental results. © 1992, Cambridge University Press. All rights reserved.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 10
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    Buoyancy-driven mean flow in a long channel with a hydraulically constrained exit condition (1999)
    Cambridge University Press
    Details
    Publication Date: 1999-11-10
    Description: Convection plays a major role in a variety of natural hydrodynamic systems. Those in which convection drives exchange flows through a lateral contraction and/or over a sill form a special class with typical examples being the Red and Mediterranean Seas, the Persian Gulf, and the fjords that indent many coastlines. The present work focuses on the spatial distribution and scaling of the density difference between the inflowing and outflowing fluid layers. Using a long water-filled channel, fitted with buoyancy sources at its upper surface, experiments were conducted to investigate the influence of the geometry of the strait and the channel as well as the magnitude of the buoyancy flux. Two different scaling laws, one by Phillips (1966), and one by Maxworthy (1994, 1997) were compared with the experimental results. It has been shown that a scaling law for which g′ = k B0 2/3x/h4/3 best describes the distribution of the observed density difference along the channel, where B0 is the buoyancy flux, x the distance from the closed end of the channel, h its height at the open end (sill) and k a constant that depends on the details of the channel geometry and flow conditions. This result holds for the experimental results and appears to be valid for a number of natural systems as well.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Cambridge University Press
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