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  • PROPULSION SYSTEMS  (3)
  • FLUID MECHANICS  (2)
  • FTIR  (2)
  • dormancy  (2)
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  • 1
    Digitale Medien
    Digitale Medien
    Springer
    Journal of atmospheric chemistry 30 (1998), S. 131-140 
    ISSN: 1573-0662
    Schlagwort(e): FTIR ; 3D Modelling
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Geologie und Paläontologie
    Notizen: Abstract We outline how ground-based Fourier transform infrared (FTIR) measurements of stratospheric trace species, obtained with high temporal resolution, could be used to detect filaments of polar vortex air at mid-latitudes and therefore test high spatial resolution chemical transport models (CTMs). Vertical column abundances of HCl, ClONO2, HNO3, N2O and HF have been obtained from FTIR solar absorption measurements made throughout the day from Aberdeen, UK (57°N, 2°W) on several days during winter/spring 1993/94 and 1994/95. The short-timescale (∼ 2 hours) variability observed in the columns is attributed to real atmospheric variations and is often associated with the passage of high latitude air over Aberdeen. This is confirmed by 3D modelling studies which qualitatively reproduce and rationalise the observed changes in the column data on January 19 1994, January 20 1995 and February 26 1995. We describe the viewing geometry of ground-based FTIR measurements and we suggest a measurement strategy which should maximise the information retrieved on horizontal gradients in stratospheric trace species columns from FTIR measurements.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    ISSN: 1573-0662
    Schlagwort(e): FTIR ; 3D Modelling
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Geologie und Paläontologie
    Notizen: Abstract Vertical column abundances of HCl, ClONO2, HF and HNO3 have been obtained from infrared solar absorption measurements made at Aberdeen, UK (57°N, 2°W) during the periods January 13 1994 - May 8 1994 and November 23 1994 - April 19 1995. The measurements reveal the partitioning of inorganic chlorine (Cly) inside and outside the polar vortex during these two winter and spring periods. Stratospheric temperatures within the northern polar vortex during 1993/94 were not cold throughout January and most of February. The measurements reported here suggest that following a brief period of chlorine activation in late February and early March, the active chlorine within the vortex recovered rapidly to form ClONO2 resulting in in-vortex ClONO2 columns of 7 × 1015 molecules cm-2. In contrast, measurements during January 1995 suggest extensive invortex activation with in-vortex HCl + ClONO2 as low as 3.6×1015 molecules cm-2. High day-to-day variability in the ClONO2 columns observed during February is evidence for the transport of ClONO2 rich air from high to mid latitudes during the late winter. The implications for mid latitude O3 loss are discussed. A preliminary comparison of the HCl, ClONO2, and HNO3 column data from winter 94/95 with a three-dimensional chemical transport model shows that the model generally reproduces well the day-to-day variability and absolute magnitude of the observed columns, especially for HNO3 outside of the vortex.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Springer
    Plant growth regulation 14 (1994), S. 51-59 
    ISSN: 1573-5087
    Schlagwort(e): bush encroachment ; Dichrostachys cinerea ; dormancy ; germination ; impermeability ; natural factors ; seed
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstracts Dichrostachys cinerea seeds are impermeable to water and do not germinate readily. The plant, however, contributes to a bush encroachment problem, minimising visibility in wildlife reserves and reducing the area available for grazing. Natural dormancy-breaking conditions must therefore exist, promoting the germinability of these normally dormant seeds. Diurnal temperature fluctuations (50°C/15°C), especially when combined with moisture were found to break dormancy. High temperatures, such as those generated by fire, destroyed seeds. Seeds ingested by herbivorous browsers such as nyala, became permeable. Seed burial for 48 weeks, was a more effective treatment than storage in promoting permeability. Distribution of D. cinerea will therefore be restricted to areas in which these conditions or factors occur. Seeds germinated optimally at 30δC in the laboratory.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    Springer
    Plant growth regulation 11 (1992), S. 201-209 
    ISSN: 1573-5087
    Schlagwort(e): Seed coat structure ; dormancy ; permeability ; Dichrostachys cinerea ; natural dormancy-breaking factors ; inhibitors
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract An understanding of dormancy mechanisms is of ecological and economic importance. Identification of the level at which dormancy is imposed appears to be species specific. The variation brought about by this therefore requires that developmental studies be included in seed coat dormancy experiments. In most cases, a site of permeability can be identified during the developmental process, and this information can be utilized later to remove dormancy. Under natural conditions, the removal of seed coat dormancy requires the interaction of a number of ecological and physiological dormancy-breaking cues.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Publikationsdatum: 2019-06-27
    Beschreibung: The interaction between the oscillations in the combustor and the wave system in the nozzle (required in combustion instability analysis of rocket engines) can be determined once the nozzle admittance is known. Experimental and theoretical methods of determining the admittance of nozzles subjected to axial oscillations are discussed. One-dimensional nozzle admittances were measured by an impedance tube technique modified to account for the presence of a mean flow. Crocco's nozzle admittance theory is applied to the prediction of admittances for several test nozzles.
    Schlagwort(e): PROPULSION SYSTEMS
    Materialart: Journal of Sound and Vibration; 30; Sept. 22
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    Publikationsdatum: 2019-06-27
    Beschreibung: Crocco's three-dimensional nozzle admittance theory is extended to be applicable when the amplitudes of the combustor and nozzle oscillations increase or decrease with time. An analytical procedure and a computer program for determining nozzle admittance values from the extended theory are presented and used to compute the admittances of a family of liquid-propellant rocket nozzles. The calculated results indicate that the nozzle geometry entrance Mach number and temporal decay coefficient significantly affect the nozzle admittance values. The theoretical predictions are shown to be in good agreement with available experimental data.
    Schlagwort(e): PROPULSION SYSTEMS
    Materialart: NASA-CR-121129
    Format: application/pdf
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    Publikationsdatum: 2019-07-13
    Beschreibung: Computer program for predicting admittances of slowly converging nozzles and acoustic liners in three dimensional acoustic field
    Schlagwort(e): FLUID MECHANICS
    Materialart: NASA-CR-119941
    Format: application/pdf
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    Publikationsdatum: 2019-07-13
    Beschreibung: Experiments were performed to check the applicability of existing acoustic liner design procedures. The performance of three different liner configurations was tested in a duct containing three-dimensional wave motion and a one-dimensional mean flow past the liner surface. Both the local liner admittance and the overall wave attenuation provided by various liner-nozzle combinations were measured with sonic flow at the nozzle throat. The experimental data are compared with predictions from current theoretical analyses, and the comparison is used to evaluate the theories.
    Schlagwort(e): FLUID MECHANICS
    Materialart: AIAA PAPER 74-61 , Aerospace Sciences Meeting; Jan 30, 1974 - Feb 01, 1974; Washington, DC
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 9
    Publikationsdatum: 2019-07-13
    Beschreibung: The three dimensional nozzle admittance, an important parameter in combustion instability studies, was experimentally measured for several nozzle configurations. The admittance values were obtained using a modification of the classical impedance tube technique. The modified impedance tube method measures the admittance of a duct termination in the presence of one dimensional mean flow and three dimensional oscillations. Values of the nozzle admittance were obtained from pressure amplitude measurements taken at discrete points along the length of the tube. To determine the effects of nozzle geometry, nozzles were tested with half-angles of 15, 30, and 45 degrees and entrance Mach numbers of 0.08, 0.16, and 0.20. The admittance results are presented as functions of nondimensional frequency for mixed first tangential-longitudinal modes. These results are compared with available theoretical predictions and favorable agreement between theory and experiment is shown.
    Schlagwort(e): PROPULSION SYSTEMS
    Materialart: AIAA PAPER 72-666 , American Institute of Aeronautics and Astronautics, Fluid and Plasma Dynamics Conference; Jun 26, 1972 - Jun 28, 1972; Boston, MA
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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