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  • 1
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    Shear-generated turbulence in the equatorial Pacific produced by small vertical-scale flow features (2015)
    Wiley
    Details
    Publication Date: 2015-05-10
    Description: We investigate the characteristics of shear–generated turbulence in the natural environment by considering data from a number of cruises in the western equatorial Pacific. In this region the vertical shear of the flow is dominated by flow structures that have a relatively small vertical scale of O(10m). Combining data from all cruises we find a strong relationship between the turbulent dissipation rate, ϵ , vertical shear, S , and buoyancy frequency, N . Examination of ϵ at a fixed value of Richardson number, Ri = N 2 ∕ S 2 , shows that for a wide range of values of N , where u t is an appropriate velocity scale which we assume to be the horizontal velocity scale of the turbulence. The implied vertical length scale, ℓ v = u t ∕ N , is consistent with theoretical and numerical studies of stratified turbulence. Such behavior is found for Ri  〈 0.4. The vertical diffusion coefficient then scales as at a fixed value of Richardson number. The amplitude of ϵ is found to increase with decreasing Ri , but only modestly, and certainly less dramatically than suggested by some parameterization schemes. Provided the shear generating the turbulence is resolved our results point to a way to parameterize the unresolved turbulence. This article is protected by copyright. All rights reserved.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Flow and mixing in Ascension, a steep, narrow canyon (2011)
    Wiley
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    Publication Date: 2011-07-20
    Description: A thin gash in the continental slope northwest of Monterey Bay, Ascension Canyon, is steep, with sides and axis both strongly supercritical to M2 internal tides. A hydrostatic model forced with eight tidal constituents shows no major sources feeding energy into the canyon, but significant energy is exchanged between barotropic and baroclinic flows along the tops of the sides, where slopes are critical. Average turbulent dissipation rates observed near spring tide during April are half as large as a two week average measured during August in Monterey Canyon. Owing to Ascension's weaker stratification, however, its average diapycnal diffusivity, 3.9 × 10−3 m2 s−1, exceeded the 2.5 × 10−3 m2 s−1 found in Monterey. Most of the dissipation occurred near the bottom, apparently associated with an internal bore, and just below the rim, where sustained cross-canyon flow may have been generating lee waves or rotors. The near-bottom mixing decreased sharply around Ascension's one bend, as did vertically integrated baroclinic energy fluxes. Dissipation had a minor effect on energetics, which were controlled by flux divergences and convergences and temporal changes in energy density. In Ascension, the observed dissipation rate near spring tide was 2.1 times that predicted from a simulation using eight tidal constituents averaged over a fortnightly period. The same observation was 1.5 times the average of an M2-only prediction. In Monterey, the previous observed average was 4.9 times the average of an M2-only prediction.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
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    From tides to mixing along the Hawaiian ridge (2003)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2003-07-19
    Description: The cascade from tides to turbulence has been hypothesized to serve as a major energy pathway for ocean mixing. We investigated this cascade along the Hawaiian Ridge using observations and numerical models. A divergence of internal tidal energy flux observed at the ridge agrees with the predictions of internal tide models. Large internal tidal waves with peak-to-peak amplitudes of up to 300 meters occur on the ridge. Internal-wave energy is enhanced, and turbulent dissipation in the region near the ridge is 10 times larger than open-ocean values. Given these major elements in the tides-to-turbulence cascade, an energy budget approaches closure.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Rudnick, Daniel L -- Boyd, Timothy J -- Brainard, Russell E -- Carter, Glenn S -- Egbert, Gary D -- Gregg, Michael C -- Holloway, Peter E -- Klymak, Jody M -- Kunze, Eric -- Lee, Craig M -- Levine, Murray D -- Luther, Douglas S -- Martin, Joseph P -- Merrifield, Mark A -- Moum, James N -- Nash, Jonathan D -- Pinkel, Robert -- Rainville, Luc -- Sanford, Thomas B -- New York, N.Y. -- Science. 2003 Jul 18;301(5631):355-7.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Scripps Institution of Oceanography, La Jolla, CA 92093-0213, USA. drudnick@ucsd.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/12869758" 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
    Published by American Association for the Advancement of Science (AAAS)
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  • 4
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    Sensitivity of internal tide generation in Hawaii (2012)
    Wiley
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    Publication Date: 2012-05-24
    Description: Energy from the barotropic tide is transferred into the baroclinic tide over topographic gradients, which provides a mechanism for the ocean boundaries to communicate with the deep ocean, to close energy budgets, and as a source of flux affecting nutrient supply and larval transport. Understanding the temporal variability of the conversion from barotropic to baroclinic tides is critical to our understanding of these processes. Using a numerical model and its adjoint, we examine the sensitivity of tidal conversion at Kaena Ridge in Hawaii. We find a sensitivity to changes in the upper ocean due to a phase difference between the pressure anomaly and tidal velocity caused by internal waves generated on the opposite slope of the ridge; however, we also find that conversion is equally as sensitive to local, deep stratification changes.
    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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  • 5
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    Numerical study on tidal mixing along the shelf break in the Green Belt in the southeastern Bering Sea (2013)
    Wiley
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    Publication Date: 2013-11-09
    Description: Tidal mixing and its associated iron and nutrients flux from a subsurface layer along the shelf break has been considered as one of the key processes to maintain the high summertime biological productivity in the Green Belt in the southeastern Bering Sea. In the present study, tidal mixing near the shelf break is examined with a three-dimensional high-resolution numerical model to quantify the enhanced mixing and to reveal the underlying physical mechanisms based on the different characteristics of diurnal and semi-diurnal internal waves. Strong turbulent mixing with energy dissipation rates of over 1 × 10 -8 W/kg is reproduced along the Green Belt in the numerical model forced by barotropic diurnal and/or semi-diurnal tides at open boundaries. The energy dissipation off the shelf break near the sea surface is enhanced due to the semi-diurnal internal waves, whereas the dissipation near the bottom of the shelf break is enhanced by the diurnal topographically trapped waves. An additional experiment with stratification representative of winter conditions shows a significant influence of stratification on the energy dissipation off the shelf break due to the change in features of both diurnal and semi-diurnal internal waves. Low-mode semi-diurnal baroclinic energy flux from the Aleutian Passes is shown to increase the energy dissipation along the shelf slope between Pribilof and Zhemchug Canyons. These results suggest that the strong vertical mixing along the shelf break induced by the diurnal and semi-diurnal tides both play important roles in maintaining the iron and nutrients supply along the Green Belt.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
    Electronic Resource
    Electronic Resource
    Distribution of Antithyroid Activity in Tissues (1944)
    [s.l.] : Nature Publishing Group
    Nature 154 (1944), S. 639-639 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] CONTINUING our investigation of the antithyroid function of paraxanthine and related compounds1, we have carried out estimations of the antithyroid activity in mammalian tissues and blood. All the extracts were made by methods similar to that described in our previous ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/154639a0
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  • 7
    Electronic Resource
    Electronic Resource
    Non-adaptive Characters in Evolution (1951)
    [s.l.] : Nature Publishing Group
    Nature 168 (1951), S. 700-701 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The subject is controversial; many biologists believe that much differentiation, especially of the minor or trivial differences of micro-evolution, is non-adaptive2. Also the subject is complex, and not one that can be adequately discussed in letters in Nature. But it may be worth while stating ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/168700b0
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  • 8
    Electronic Resource
    Electronic Resource
    Non-adaptive or Neutral Characters in Evolution (1951)
    [s.l.] : Nature Publishing Group
    Nature 168 (1951), S. 1049-1049 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/1681049c0
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  • 9
    Electronic Resource
    Electronic Resource
    Paraxanthine as a Natural Antithyroid Substance (1943)
    [s.l.] : Nature Publishing Group
    Nature 151 (1943), S. 728-730 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] MANY substances have been found to have anti-thyroid activity in the vertebrate body, some of them natural constituents of the body. But it has never been clear to what extent these substances exert their antithyroid properties in normal life. In this letter we report some results which have ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/151728c0
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  • 10
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    CONCEPTS OUT OF CONTEXT (1952)
    Oxford : Periodicals Archive Online (PAO)
    The British journal for the philosophy of science. 3:[9/12] (1952:May-1953:Feb.) 86 
    Details
    ISSN: 0007-0882
    Topics: Natural Sciences in General , Philosophy
    Notes: DISCUSSIONS
    URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pao:&rft_dat=xri:pao:article:4064-1952-003-09-000019
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