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  • 1
    Publication Date: 2012-05-25
    Description: Warming experiments are increasingly relied on to estimate plant responses to global climate change. For experiments to provide meaningful predictions of future responses, they should reflect the empirical record of responses to temperature variability and recent warming, including advances in the timing of flowering and leafing. We compared phenology (the timing of recurring life history events) in observational studies and warming experiments spanning four continents and 1,634 plant species using a common measure of temperature sensitivity (change in days per degree Celsius). We show that warming experiments underpredict advances in the timing of flowering and leafing by 8.5-fold and 4.0-fold, respectively, compared with long-term observations. For species that were common to both study types, the experimental results did not match the observational data in sign or magnitude. The observational data also showed that species that flower earliest in the spring have the highest temperature sensitivities, but this trend was not reflected in the experimental data. These significant mismatches seem to be unrelated to the study length or to the degree of manipulated warming in experiments. The discrepancy between experiments and observations, however, could arise from complex interactions among multiple drivers in the observational data, or it could arise from remediable artefacts in the experiments that result in lower irradiance and drier soils, thus dampening the phenological responses to manipulated warming. Our results introduce uncertainty into ecosystem models that are informed solely by experiments and suggest that responses to climate change that are predicted using such models should be re-evaluated.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Wolkovich, E M -- Cook, B I -- Allen, J M -- Crimmins, T M -- Betancourt, J L -- Travers, S E -- Pau, S -- Regetz, J -- Davies, T J -- Kraft, N J B -- Ault, T R -- Bolmgren, K -- Mazer, S J -- McCabe, G J -- McGill, B J -- Parmesan, C -- Salamin, N -- Schwartz, M D -- Cleland, E E -- England -- Nature. 2012 May 2;485(7399):494-7. doi: 10.1038/nature11014.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Division of Biological Sciences, University of California San Diego, 9500 Gilman Drive 0116, La Jolla, California 92093, USA. wolkovich@biodiversity.ubc.ca〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22622576" target="_blank"〉PubMed〈/a〉
    Keywords: Artifacts ; Ecosystem ; Flowers/growth & development/physiology ; *Global Warming ; *Models, Biological ; *Periodicity ; Plant Development ; Plant Leaves/growth & development/physiology ; *Plant Physiological Phenomena ; Plants/classification ; Reproducibility of Results ; Soil/chemistry ; Temperature ; Time Factors ; *Uncertainty
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 2
    Publication Date: 2019-06-27
    Description: An experimental and analytical study has been made of the accuracy of various Preston tube calibration equations to determine local skin friction in two-dimensional supersonic and low-hypersonic flows. Experimental Preston tube calibration data from the present and previous studies were used to evaluate the calibration equations. The maximum value of the calibration parameters of the present data is more than an order of magnitude larger than that previously obtained; thereby, the evaluation of the various calibration equations is facilitated. The Preston tube technique was found to be very inaccurate in the low range of the calibration parameters. Above this range, there was a steady increase in accuracy with increasing values of the calibration parameters. No critical maximum tube diameter was found even with tubes about twice as large as the theoretical maximum allowable diameter. Of the two forms of the calibration equation previously existing, the logarithmic laws gave more accurate results than the power laws over an extended range of the calibration parameters in supersonic adiabatic flow.
    Keywords: FLUID MECHANICS
    Type: NASA-TN-D-7190 , L-8733
    Format: application/pdf
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  • 3
    Publication Date: 2019-06-27
    Description: Eight circular pitot probes ranging in size from 2 to 70 percent of the boundary-layer thickness were tested to provide experimental probe displacement results in a two-dimensional turbulent boundary layer at a nominal free-stream Mach number of 2 and unit Reynolds number of 8 million per meter. The displacement obtained in the study was larger than that reported by previous investigators in either an incompressible turbulent boundary layer or a supersonic laminar boundary layer. The large probes indicated distorted Mach number profiles, probably due to separation. When the probes were small enough to cause no appreciable distortion, the displacement was constant over most of the boundary layer. The displacement in the near-wall region decreased to negative displacement in some cases. This near-wall region was found to extend to about one probe diameter from the test surface.
    Keywords: FLUID MECHANICS
    Type: NASA-TN-D-6759 , L-8159
    Format: application/pdf
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  • 4
    Publication Date: 2019-06-27
    Description: Baronti-Libby transformation and Preston tube calibrations used to determine skin friction from turbulent velocity profiles
    Keywords: FLUID MECHANICS
    Type: NASA-TN-D-4853
    Format: application/pdf
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  • 5
    Publication Date: 2019-06-27
    Description: Experimental pitot-probe-displacement data have been obtained in a turbulent boundary layer at a local free-stream Mach number of 4.63 and unit Reynolds number of 6.46 million meter. The results of this study were compared with lower Mach number results of previous studies. It was found that small probes showed displacement only, whereas the larger probes showed not only displacement but also distortion of the shape of the boundary-layer profile. The distortion pattern occurred lower in the boundary layer at the higher Mach number than at the the lower Mach number. The maximum distortion occurred when the center of the probe was about one probe diameter off the test surface. For probes in the wall contact position, the indicated Mach numbers were, for all probes tested, close to the true profile. Pitot-probe displacement was found to increase significantly with increasing Mach number.
    Keywords: FLUID MECHANICS
    Type: NASA-TN-D-7466 , L-9253
    Format: application/pdf
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  • 6
    Publication Date: 2019-06-27
    Description: Experimental Preston tube and law-of-the-wall study of turbulent skin friction on axisymmetric bodies at supersonic speeds
    Keywords: FLUID MECHANICS
    Type: NASA-TN-D-5660 , L-6686
    Format: application/pdf
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