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  • ACOUSTICS  (8)
  • Furanocoumarins  (4)
  • Positron annihilation  (3)
  • 1
    Electronic Resource
    Electronic Resource
    Behaviour of positrons in binary alloys (1974)
    Springer
    Applied physics 4 (1974), S. 213-215 
    Details
    ISSN: 1432-0630
    Keywords: Positron annihilation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The pseudopotential picture of the positron in a binary alloy is developed. It is shown that the positron is usually preferentially attracted to one sort of atom in the alloy. This relative positron affinity is associated with the positron pseudopotential difference between the different sorts of atom and calculations of this quantity are presented for a number of 50 at % alloys.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00884231
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Positron distribution in metals (1974)
    Springer
    Applied physics 3 (1974), S. 417-419 
    Details
    ISSN: 1432-0630
    Keywords: Positron annihilation ; Positron pseudopotential
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract A positron wave function incorporating the proper crystal symmetry is calculated for Al using the positron pseudopotential method. The positron ground state energy was also calculated and it was found to be in good agreement with the previous Wigner-Seitz calculations. The pseudopotential matrix elements are shown to be small and thus very accurate calculations can be performed using low order perturbation theory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00885849
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  • 3
    Electronic Resource
    Electronic Resource
    Positron trapping at defects in evaporated films (1974)
    Springer
    Applied physics 4 (1974), S. 333-337 
    Details
    ISSN: 1432-0630
    Keywords: Positron annihilation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The trapping of positrons at defects in evaporated copper and lead films has been investigated. Measurements of the positron lifetime spectra in high purity films over a wide range of deposition rates and a limited range of substrate temperatures can be interpreted in terms of positron trapping at both grain boundaries and dislocations in the copper films and at grain boundaries only in the lead films. Isochronal annealing studies indicate that recovery and recrystallization of these films is qualitatively similar to that of the bulk metal after deformation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00928388
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  • 4
    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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  • 5
    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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  • 6
    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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  • 7
    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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  • 8
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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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  • 9
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    The prediction of helicopter tail rotor noise on the flight path (1987)
    In:  Other Sources
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    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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  • 10
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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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