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  • Engineering  (50)
  • Geophysics  (50)
  • Inorganic Chemistry
  • 1995-1999  (125)
  • 1950-1954
  • 1930-1934
  • 1920-1924
  • 1997  (125)
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  • 1995-1999  (125)
  • 1950-1954
  • 1930-1934
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  • 1
    Publication Date: 2019-07-17
    Description: The POLAR satellite often observes upflowing ionospheric ions (UFls) in and near the auroral oval on southern perigee (approximately 5000 km altitude) passes. We present the UFI features observed by the thermal ion dynamics experiment (TIDE) and the toroidal imaging mass-angle spectrograph (TIMAS) in the dusk-dawn sector under two different geomagnetic activity conditions in order to elicit their relationships with auroral forms, wave emissions, and convection pattern from additional POLAR instruments. During the active interval, the ultraviolet imager (UVI) observed a bright discrete aurora on the dusk side after the substorm onset and then observed a small isolated aurora form and diffuse auroras on the dawn side during the recovery phase. The UFls showed clear conic distributions when the plasma wave instrument (PWI) detected strong broadband wave emissions below approximately 10 kHz, while no significant auroral activities were observed by UVI. At higher latitudes, the low-energy UFI conics gradually changed to the polar wind component with decreasing intensity of the broadband emissions. V-shaped auroral kilometric radiation (AKR) signatures observed above approximately 200 kHz by PWI coincided with the region where the discrete aurora and the UFI beams were detected. The latitude of these features was lower than that of the UFI conics. During the observations of the UFI beams and conics, the lower-frequency fluctuations observed by the electric field instrument (EFI) were also enhanced, and the convection directions exhibited large fluctuations. It is evident that large electrostatic potential drops produced the precipitating electrons and discrete auroras, the UFI beams, and the AKR, which is also supported by the energetic plasma data from HYDRA. Since the intense broadband emissions were also observed with the UFIs. the ionospheric ions could be energized transversely before or during the parallel acceleration due to the potential drops.
    Keywords: Geophysics
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  • 2
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 13 (1997), S. 47-49 
    ISSN: 1069-8299
    Keywords: nonlinear structural analysis ; arc-length algorithm ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In this paper, we have proved in theory that the sign of the current stiffness matrix provides a correct indicator for determining the sign of the loading parameter in the arc-length algorithm before the first bifurcation point is encountered, but may not be the case thereafter. © 1997 John Wiley & Sons, Ltd.
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  • 3
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 40 (1997), S. 887-903 
    ISSN: 0029-5981
    Keywords: multigrid ; adaptive agglomeration ; additive correction ; anisotropic grids ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In the computational simulation of fluid flow and scalar transport, multigrid iterative solution techniques often fail or stall when the discrete linearized equations have strongly anisotropic coefficients. In the present work, an adaptive agglomeration algorithm for forming coarse grids is presented that allows multigrid techniques to work efficiently for equation sets with anisotropic coefficients. The adaptive agglomeration is defined by two rules and several guidelines that follow from a physical interpretation of the performance of iterative solvers like Gauss-Seidel. The effectiveness of the adaptive agglomeration algorithm is demonstrated for a wide range of test cases. © 1997 by John Wiley & Sons, Ltd.
    Additional Material: 10 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 21 (1997), S. 825-843 
    ISSN: 0363-9061
    Keywords: fracture modelling ; granular materials ; numerical modelling ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: This paper describes the computer algorithms used in a numerical simulation of the compression of an aggregate of crushable grains. It has been used in a model for the evolution of a granular medium under one-dimensional compression, in which the probability of fracture for individual particles is a function of applied stress, particle-size and co-ordination number. The information relating to the particles is represented in a compact way on the computer which allows the number of particles produced to become sufficiently large for satisfactory comparisons to be made with experimental data and which allows information, such as the positions and sizes of the particles, to be easily extracted. An algorithm based on the representation is used to locate neighbouring particles in a way which does not deteriorate unacceptably in terms of speed as the number of particles increases. © 1997 by John Wiley & Sons, Ltd.
    Additional Material: 13 Ill.
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  • 5
    ISSN: 0044-2313
    Keywords: Arylxenon trifluoromethanesulfonates ; electrophilic aromatic substitution ; xenontrifluoroacetate trifluoromethanesulfonate ; NMR spectra ; X-ray crystal structure ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Die direkte Synthese von Arylxenontrifluormethansulfonaten durch elektrophile SubstitutionBei der Reaktion von Xenonbis(trifluoracetat) mit Trifluormethansulfonsäure wird die neue, hochreaktive, unsymmetrische Xenon-Sauerstoff-Verbindung CF3COOXeOSO2CF3 erzeugt. Benzolderivate mit elektronenziehenden Substituenten wie F, CF3, Cl und NO2 werden von diesem Intermediat unter Bildung von Arylxenontrifluormethansulfonaten elektrophil angegriffen. Über diese Eintopfsynthese wurden Trifluormethansulfonate mit den Kationen [Xe(2,4,6-F3C6H2)]+, [Xe(2-F-5-NO2C6H3)]+, [Xe(2-F-5-CF3C6H3)]+ und [Xe(3,5-(CF3)2C6H3)]+ synthetisiert. Alle Verbindungen wurden durch ihre NMR-, Massen- und Schwingungsspektren charakterisiert.Zusätzlich wurden mehrere neue Arylxenontrifluormethansulfonate als Produkte der Umsetzungen von 1,3-F2C6H4 und weiteren desaktivierten Benzolen mit Xenon(trifluoracetat)trifluormethansulfonat anhand der 129Xe-NMR-Spektren identifiziert.Fluorsubstituenten in ortho-Position zu Xenon erhöhen signifikant die thermische Stabilität der Arylxenontrifluormethansulfonate.Die Molekülstruktur von [Xe(2,6-F2C6H3)][OSO2CF3] wurde durch eine Einkristallröntgenstrukturanalyse bestimmt. Die Arylxenoneinheit koordiniert schwach mit einem Sauerstoffatom des CF3SO3-Anions. Die Verbindung kristallisiert in der triklinen Raumgruppe mit a = 880.9(3) pm, b = 1093.9(5) pm, c = 1209.8(5) pm, α = 89.04(4)°, β = 74.23(3)°, γ = 86.03(3)°, Z = 4.
    Notes: The reaction of xenonbis(trifluoroacetate) and trifluoromethanesulfonic acid (triflic acid) gave the new, highly reactive unsymmetrical xenon-oxo species CF3COOXeOSO2CF3. Benzene derivates, containing electron withdrawing substituents such as -F, -CF3, -Cl or -NO2 were electrophilic attacked by this intermediate to yield arylxenon trifluoromethanesulfonates. Via this one-pot synthesis trifluoromethanesulfonates with the cations [Xe(2,4,6-F3C6H2)]+, [Xe(2-F-5-NO2C6H3)]+, [Xe(2-F-5-CF3C6H3)]+ and [Xe(3,5-(CF3)2C6H3)]+ were prepared. All compounds were characterized by their NMR, mass, and vibrational spectra.Additionally, several new arylxenon trifluoromethanesulfonates were detected by 129Xe-NMR spectroscopy as products of the reaction of 1,3-F2C6H4 and further deactivated benzenes with xenontrifluoroacetate trifluoromethane sulfonate.Fluoro substituents in ortho position to xenon significantly increase the thermal stability of the arylxenon trifluoromethanesulfonates obtained.The molecular structure of [Xe(2,6-F2C6H3)][OSO2CF3] was determined by single crystal diffraction methods. The arylxenon unit is weakly coordinated by one oxygen atom of the CF3SO3 anion. The salt crystallizes in the triclinic space group P1, a = 880.9(3) pm, b = 1093.9(5) pm, c = 1209.8(5) pm, α = 89.04(4)°, β = 74.23(3)°, γ = 86.03(3)°, Z = 4.
    Additional Material: 7 Ill.
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  • 6
    Publication Date: 2019-07-10
    Description: The objectives, design and results of the sensor systems for the combined sporadic structures and layers (CSSL) payload are analyzed. The CSSL main objectives were to: validate current models of mesospheric sodium chemistry; explore the relationship between turbulence and Na fluctuations; and to explore the relationship between high latitude electric fields and the formation of Na anomalies.
    Keywords: Geophysics
    Type: ; 299-304
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  • 7
    Publication Date: 2019-07-13
    Description: With Observations from the retarding ion mass spectrometer on the Dynamics Explorer I from 1981 through 1984, we examine the He(+) to H(+) density ratios as a function of altitude, latitude, season, local time, geomagnetic and solar activity. We find that the ratios are primarily a function of geocentric distance and the solar EUV input. The ratio of the densities, when plotted as a function of geocentric distance, decrease by an order of magnitude from 1 to 4.5 R(sub E). After the He(+) to H(+) density ratios are adjusted for the dependence on radial distance, they decrease nonlinearly by a factor of 5 as the solar EUV proxy varies from about 250 to about 70. When the mean variations with both these parameters are removed, the ratios appear to have no dependence on geomagnetic activity and weak dependence on local time or season, geomagnetic latitude, and L shell.
    Keywords: Geophysics
    Type: NASA-CR-204658 , Paper-96JA02176 , NAS 1.26-204658 , Journal of Geophysical Research (ISSN 0148-0227); 102; A2; 2279-2289
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  • 8
    Publication Date: 2019-07-17
    Description: The UVI imager on board the POLAR satellite offers the opportunity to obtain high time resolution global auroral images. The spectral resolution of the imager is sufficient to separate the auroral emission from the scattered sunlight, even when the entire auroral zone is sunlit. The energy flux of the precipitating electrons is derived from the surface brightness through the LBH-long filter. Global images which have the dayglow removed are spatially integrated to yield the total hemispheric electron energy flux. This parameter, the hemispheric power, has found much application in ionospheric modeling. It can also be derived from electron spectra measured along the track of the NOAA/TIROS satellites that are combined with average empirical auroral precipitation patterns. We show that the hemispheric power input derived from the two-dimensional images represents a substantial improvement in the temporal variability of this parameter. We present an example for the period of 19/20 May 1996 by comparing power indices derived from NOAA/TIROS measurements with those derived from the UVI images.
    Keywords: Geophysics
    Type: Geophysical Research Letters
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  • 9
    Publication Date: 2019-08-16
    Description: Changes in major global dynamical phenomena in the Earth's atmosphere are manifested in the time series of atmospheric angular momentum (AAM), as determined directly from meteorological observations and indirectly from geodetic observations of small fluctuations in the rotation of the solid Earth which are proportional to length of day. AAM fluctuations are intimately linked with energetic processes throughout the whole atmosphere and also with the stresses at the Earth's surface produced largely by turbulent momentum transport in the oceanic and continental boundary layers and by the action of normal pressure forces on orographic features. A stringent test of any numerical global circulation model (GCM) is therefore provided by a quantitative assessment of its ability to represent AAM fluctuations on all relevant timescales, ranging from months to several years. From monthly data provided by the Atmospheric Model Intercomparison Project (AMIP) of the World Climate Research Programme, we have investigated seasonal and interannual fluctuations and the decadal mean in the axial component of AAM in 23 AMIP GCMs over the period 1979-1988. The decadal means are generally well simulated, with the model median value (1.58 x 10(exp 26) kg sq m/s) being only 3.5% larger than the observed mean and with 10 of the models being within 5% of the observed. The seasonal cycle is well reproduced, with the median amplitude of the models seasonal standard deviations being only 2.4% larger than observed. Half the seasonal amplitudes lie within 15% of the observed, and the median correlation found between the observed and model seasonal cycles is 0.95. The dominant seasonal error is an underestimation of AAM during northern hemisphere winter associated with errors in the position of subtropical jets. Less robust are the modeled interannual variations, although the median correlation of 0.61 between model simulations and observed AAM is statistically significant. The two El Nino-Southem Oscillation events that occurred during the AMIP decade 1979-1988 have the expected positive AAM anomalies, although the AAM signature of the 1982-1983 event tends to be underestimated and that of the 1986-1987 event overestimated.
    Keywords: Geophysics
    Type: Paper-97JD00699 , Journal of Geophysical Research (ISSN 0148-0227); 102; D14; 16,423-16,438
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  • 10
    Publication Date: 2019-08-15
    Description: Geotail plasma and field measurements at -95 R(sub E) are compared with extensive ground-based, near-Earth, and geosynchronous measurements to study relationships between auroral activity and magnetotail dynamics during the expansion phases of two substorms. The studied intervals are representative of intermittent, moderate activity. The behavior of the aurora and the observed effects at Geotail for both events are harmonized by the concept of the activation of near-Earth X lines (NEXL) after substorm onsets, with subsequent discharges of one or more plasmoids down the magnetotail. The plasmoids must be viewed as three-dimensional structures which are spatially limited in the dawn-dusk direction. Also, reconnection at the NEXL must proceed at variable rates on closed magnetic field lines for significant times before beginning to reconnect lobe flux. This implies that the plasma sheet in the near-Earth magnetotail is relatively thick in comparison with an embedded current sheet and that both the NEXL and distant X line can be active simultaneously. Until reconnection at the NEXL engages lobe flux, the distant X line maintains control of the poleward auroral boundary. If the NEXL remains active after reaching the lobe, the auroral boundary can move poleward explosively. The dynamics of high-latitude aurora in the midnight region thus provides a means for monitoring these processes and indicating when significant lobe flux reconnects at the NEXL.
    Keywords: Geophysics
    Type: NASA-CR-205249 , Paper-97JA00307 , NAS 1.26:205249 , Journal of Geophysical Research (ISSN 0148-0227); 102; A5; 9553-9572
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