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  • 1
    Publication Date: 2013-08-31
    Description: The turbulent boundary layer driven by a freestream velocity that varies sinusoidally in time around a zero mean is considered. The flow has a rich behavior including strong pressure gradients, inflection points, and reversal. A theory for the velocity and stress profiles at high Reynolds number is formulated. Well-resolved direct Navier-Stokes simulations are conducted over a narrow range of Reynolds numbers, and the results are compared with the theoretical predictions. The flow is also computed over a wide range of Reynolds numbers using a new algebraic turbulence model; the results are compared with the direct simulations and the theory.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: A-87220 , NAS 1.15:89460 , NASA-TM-89460
    Format: application/pdf
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  • 2
    Publication Date: 2014-07-15
    Type: NACA-TN-1816
    Format: application/pdf
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  • 3
    Publication Date: 2019-07-27
    Description: The turbulent boundary layer driven by a freestream velocity that varies sinusoidally in time around a zero mean is considered. The flow has a rich behavior including strong pressure gradients, inflection points, and reversal. A theory for the velocity and stress profiles at high Reynolds number is formulated. Well-resolved direct Navier-Stokes simulations are conducted over a narrow range of Reynolds numbers, and the results are compared with the theoretical predictions. The flow is also computed over a wide range of Reynolds numbers using a new algebraic turbulence model; the results are compared with the direct simulations and the theory.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Symposium on Turbulent Shear Flows; Sept. 7-9, 1987; Toulouse; France
    Format: text
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  • 4
    Publication Date: 1986-06-06
    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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  • 5
    ISSN: 1432-2242
    Keywords: Trimorphic incompatibility ; Pontederia cordata L.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Pontederia cordata L. (Pontederiaceae), a perennial diploid, possesses the rare genetic polymorphism tristyly. A controlled pollination programme was conducted over a three year period, under glasshouse conditions, on 36 clones of P. cordata var. cordata to examine the nature of the self-incompatibility system. The three major findings of the pollination study were: (1) the three floral morphs display different levels of self-incompatibility, (2) pollen from the two anther levels within a flower exhibits different compatibility behaviour in self-pollinations, (3) considerable individual genetic variation in the expression of self-incompatibility is evident among clones within floral morphs. Similar results were also obtained from a smaller study on 15 clones of P. cordata var. lancifolia conducted over a 6 month period. In common with other Pontederia species the mid-styled morph (M) of P. cordata produces large amounts of seed when self-pollinated with pollen from long-level anthers. A developmental model is proposed to explain the high level of self-compatibility of the M morph in Pontederia species. Self-pollination of segregating progenies from M and S morphs of known incompatibility status demonstrated that the expression of incompatibility is closely associated with style length. It is suggested that overall differences in incompatibility behaviour among the floral morphs may be due to the pleiotropic effects of major genes controlling sub-characters of the tristylous syndrome, rather than linked modifier genes. However, the variable expression of trimorphic incompatibility within floral morphs suggests that this variation may be polygenic in origin.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1432-1939
    Keywords: Pontederia cordata ; Bombus ; Tristyly ; Pollination ; Behavior
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The foraging behavior of the pollinators of tristylous Pontederia cordata was studied to determine if differences in floral morphology would lead to preferential visitation of the floral morphs. Although nectar production is not different in the three floral morphs, differences in the production and size of pollen grains produced by the three anther levels results in the morphs offering variable amounts of resources to pollen-collecting insects. Bumblebees (Bombus spp.) and the solitary bee Melissodes apicata used P. cordata primarily as a nectar source and therefore did not seem to exhibit any morph preference. In contrast, honeybees visited flowers mainly for pollen and preferred to forage on long-level anthers of the short-and mid-styled morphs. An analysis of the composition of corbicular pollen loads indicated that, relative to the frequency of production in the population: 1) honeybees collected an excess of pollen from long-level anthers; 2) bumblebees collected the three types of pollen without any apparent preference; and 3) M. apicata preferentially collected pollen from the short-level anthers — presumably because their proboscides are modified by the presence of tiny hairs. The results suggest that P. cordata in Ontario is serviced by a diverse, unspecialized pollinator fauna which is not co-adapted to the tristylous floral polymorphism.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 66 (1987), S. 375-378 
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We observe a number of well defined peaks in the photoemission spectra from Y(0001) over the photon energy range 25 eV〈hv〈60 eV. We believe that one of the features with a binding energy of 1.7 eV is due to emission from states near the upper band edge at the Γ point and that a second nearE F originates from a surface state. We find a large peak at a binding energy of 9.6 eV which is sensitive to the quality of the surface.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Peaks in the uv photoelectron spectra from single crystal surfaces of yttrium which cannot be ascribed to the one-electron states in band structure calculations have been recently interpreted as due to hydrogen contamination. The evidence for this suggestion, however, is based on an erroneous comparison between the results of UPS experiments on polycrystalline samples exposed to hydrogen and previously published spectra from single crystal samples. In this paper we show how the spectra have been misinterpreted and comment on the consequences concerning the origin of the peaks.
    Type of Medium: Electronic Resource
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