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  • 1
    Electronic Resource
    Electronic Resource
    Identification of eight coumarins occurring with psoralen, xanthotoxin, and bergapten on leaf surfaces (1991)
    Springer
    Journal of chemical ecology 17 (1991), S. 1859-1870 
    Details
    ISSN: 1573-1561
    Keywords: Furanocoumarins ; coumarins ; mass spectrometry ; leaf surface
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Surface extracts of the leaves of five species in the Umbelliferae,Citrus limon (Rutaceae), andPsoralea bituminosa (Leguminosae) were examined for the presence of coumarins, after a previous study had shown the presence of three psoralens. In the current investigation eight more coumarins were identified by mass spectrometric techniques: the simple coumarins scopoletin, scoparone, and osthol, the linear furanocoumarins imperatorin and phellopterin, the angular furanocoumarins angelicin and pimpinellin, and the pyranocoumarin seselin. Five of these occur inApium graveolens, and scopoletin, scoparone, and imperatorin were each found in three of the species examined. The co-occurrence of all these coumarins on the surface may be significant in communication between the plant and its environment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00993733
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Dermatitis-inducing furanocoumarins on leaf surfaces of eight species of Rutaceous and Umbelliferous plants (1990)
    Springer
    Journal of chemical ecology 16 (1990), S. 693-700 
    Details
    ISSN: 1573-1561
    Keywords: Furanocoumarins ; plant surface ; dermatitis ; Rutaceae ; Umbelliferae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Eight species of Rutaceae or Umbelliferae, known to cause or suspected of causing photophytodermatitis, had the linear furanocoumarins psoralen, bergapten, and xanthotoxin on their leaf surfaces, in concentrations varying from 0.014 to 1800 /gmg/g fresh weight, equivalent to 0.17–56% of the total leaf concentration. The higher percentage generally observed for spring leaves compared to autumn leaves suggests a higher rate of transfer of these furanocoumarins to the surface in the younger leaves. Among the plants studied,Ruta graveolens had the highest surface concentrations of all three furanocoumarins. The relatively high effectiveness in causing dermatitis of some species with low surface concentrations may be explained by a more effective mechanism of transfer of the furanocoumarins to the skin. A role in the defense of the plant is suggested by their accumulation on the plant surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01016480
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Seasonal changes of furanocoumarin concentrations in leaves ofHeracleum lanatum (1990)
    Springer
    Journal of chemical ecology 16 (1990), S. 1623-1634 
    Details
    ISSN: 1573-1561
    Keywords: Furanocoumarins ; Heracleum lanatum ; leaf surface
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Concentrations of three dermatitis-inducing furanocoumarins— xanthotoxin, bergapten and psoralen—were measured in whole leaves ofHeracleum lanatum and in extracts of the leaf surface over an entire vegetative season. The concentrations of surface furanocoumarins, localized by extraction involving brief dipping in almost-boiling water followed by HPLC quantitative analysis, increased until the middle of May and decreased until maturity. The concentration on autumn leaves (new growth) was 20–100 times as high as the ones in May, or those of similar size in April. Furanocoumarin concentrations in the whole leaf at different stages of leaf development varied, being the highest April 25, then decreasing sharply with rapid leaf enlargement. Again, in the small autumn leaves the coumarin concentration was two to three times that in April. Seasonal changes in surface furanocoumarins may be important in that these compounds are postulated to form the first defense barrier of the plant.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01014095
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  • 4
    Electronic Resource
    Electronic Resource
    Influence of low-intensity ultraviolet radiation on extrusion of furanocoumarins to the leaf surface (1993)
    Springer
    Journal of chemical ecology 19 (1993), S. 939-952 
    Details
    ISSN: 1573-1561
    Keywords: Furanocoumarins ; psoralens ; Ruta graveolens ; ultraviolet radiation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Exposure ofRuta graveolens leaves to low intensity 366-nm radiation led to a ca. 20% increase in concentrations of the furanocoumarins psoralen, xanthotoxin and bergapten, as compared to leaves kept in darkness. Both direct and, even more, scattered UV radiation produced increases in total concentrations. Changes in the concentrations of individual coumarins were generally parallel. Extrusion to the surface was increased, especially in lower, older leaves exposed to the scattered radiation, where it exceeded the control by factors of eight or nine. It is suggested that this response could enhance shielding of leaves against penetration of UV into the cells and that irradiation, by exciting the furanocoumarins, could augment protection against potential microbial invaders.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00992529
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  • 5
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    The prediction of blade wake interaction noise based on a turbulent vortex model (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Blade wake interaction is defined as the broadband noise generated by the interaction of helicopter rotor blades with their own wake. Experimental observations have shown that this is a strong function of advance ratio and tip path plane angle. This paper describes how this noise source can be associated with the blade vortex interactions in the forward sector of the rotor. Measured levels of turbulence in the vortex core are used to predict the broadband noise levels with some success. However, more detailed information on the turbulence spectrum and the trajectory of the shed vortices is required before more accurate noise predictions can be made.
    Keywords: ACOUSTICS
    Type: AIAA PAPER 89-1134
    Format: text
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  • 6
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    The prediction of helicopter tail rotor noise on the flight path (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Experimental measurements on a model scale helicopter in a wind tunnel have shown that the levels radiated in the direction of flight are strongly dependent on the fuselage angle to the mean flow. Here a theoretical model is derived to explain these measurements using unsteady thickness noise as the principle source mechanism. The model includes the effect of fuselage wake turbulence which is convected through only the lower sector of the rotor disk. This causes spectral peaks which do not occur at blade passing frequencies, but rather at frequencies associated with convected flow inhomogeneities. The results are compared with measurements and show good agreement over a range of fuselage angles and mean flow speeds.
    Keywords: ACOUSTICS
    Type: AIAA PAPER 87-2747
    Format: text
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  • 7
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    A ray-acoustics approach to fuselage scattering of rotor noise (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A ray acoustics approach to fuselage scattering of rotor noise is considered. The method is based on a combination of classical geometrical acoustics and the paraxial ray approximation. The method can handle scattering by objects of arbitrary shapes and can be applied in an inhomogeneous moving medium. Applications to aeroacoustics include the scattering of blade vortex interaction (BVI) pulses by rigid scattering objects. The BVI is modeled by a rotating impulsive point force. It has been found that scattering effects of rotating sources cannot be ignored. Flow has also been found to cause a modification and displacement of the directivity pattern and the shadow zones behind scatterers.
    Keywords: ACOUSTICS
    Type: AIAA PAPER 90-4013
    Format: text
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  • 8
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    Perpendicular blade vortex interaction and its implications for helicopter noise prediction: Wave-number frequency spectra in a trailing vortex for BWI noise prediction (1993)
    In:  CASI
    Details
    Publication Date: 2019-07-20
    Description: Perpendicular blade vortex interactions are a common occurrence in helicopter rotor flows. Under certain conditions they produce a substantial proportion of the acoustic noise. However, the mechanism of noise generation is not well understood. Specifically, turbulence associated with the trailing vortices shed from the blade tips appears insufficient to account for the noise generated. The hypothesis that the first perpendicular interaction experienced by a trailing vortex alters its turbulence structure in such a way as to increase the acoustic noise generated by subsequent interactions is examined. To investigate this hypothesis a two-part investigation was carried out. In the first part, experiments were performed to examine the behavior of a streamwise vortex as it passed over and downstream of a spanwise blade in incompressible flow. Blade vortex separations between +/- one eighth chord were studied for at a chord Reynolds number of 200,000. Three-component velocity and turbulence measurements were made in the flow from 4 chord lengths upstream to 15 chordlengths downstream of the blade using miniature 4-sensor hot wire probes. These measurements show that the interaction of the vortex with the blade and its wake causes the vortex core to loose circulation and diffuse much more rapidly than it otherwise would. Core radius increases and peak tangential velocity decreases with distance downstream of the blade. True turbulence levels within the core are much larger downstream than upstream of the blade. The net result is a much larger and more intense region of turbulent flow than that presented by the original vortex and thus, by implication, a greater potential for generating acoustic noise. In the second part, the turbulence measurements described above were used to derive the necessary inputs to a Blade Wake Interaction (BWI) noise prediction scheme. This resulted in significantly improved agreement between measurements and calculations of the BWI noise spectrum especially for the spectral peak at low frequencies, which previously was poorly predicted.
    Keywords: ACOUSTICS
    Type: NASA-CR-193623 , NAS 1.26:193623
    Format: application/pdf
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  • 9
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    The application of experimental data to blade wake interaction noise prediction (1991)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Blade wake interaction noise (BWI) has been defined as the broadband noise generated by the ingestion of turbulent trailing tip vortices by helicopter rotors. This has been shown to be the dominant contributor to the subjectively important part of the acoustic spectrum for the approach stage of a helicopter flyover. A prediction method for BWI noise based on the calculated trailing vortex trajectories has been developed and estimates of the vortex turbulence have been made. These measurements were made on a trailing vortex from a split wing arrangement and did not give the spectrum of the velocity fluctuations. A recent experiment carried out to measure the turbulence associated with a trailing vortex and the application of the results to BWI noise prediction is described.
    Keywords: ACOUSTICS
    Type: NASA-CR-189461 , NAS 1.26:189461 , International Symposium on Unsteady Aerodynamics, Aeroacousticsand Aeroelasticity of Turbomachines and Propellers; Sep 15, 1991 - Sep 19, 1991; Notre Dame, IN; United States
    Format: application/pdf
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  • 10
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    Prediction of blade wake interaction noise based on a turbulent vortex model (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Keywords: ACOUSTICS
    Type: AIAA Journal (ISSN 0001-1452); 29; 1545-155
    Format: text
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