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  • 2020-2024  (22)
  • 1965-1969  (27)
  • 1
    Publication Date: 2023-01-26
    Description: At high‐latitudes, diurnal and semidiurnal variations of temperature and neutral wind velocity can originate both in the lower atmosphere (UV or infrared absorption) and in the thermosphere‐ionosphere (ion convection, EUV absorption). Determining the relative impact of different forcing mechanisms gives insight to the vertical coupling in the ionosphere. We analyze measurements from the incoherent scatter radar (ISR) facility operated by the EISCAT Scientific Association. They are complemented by meteor radar data and compared to global circulation models. The amplitudes and phases of tidal oscillations are determined by an adaptive spectral filter (ASF). Measurements indicate the existence of strong semidiurnal oscillations in a two‐band structure at altitudes ≲110 and ≳130 km, respectively. Analysis of several model runs with different input settings suggest the upper band to be forced in situ while the lower band corresponds to upward‐propagating tides from the lower atmosphere. This indicates the existence of an unexpectedly strong, in situ forcing mechanism for semidiurnal oscillations in the high‐latitude thermosphere. It is shown that the actual transition of tides in the altitude region between 90 and 150 km is more complex than described so far.
    Description: Plain Language Summary: Solar and atmospheric variability influence the ionosphere, causing critical impacts on satellite and ground‐based infrastructure. Determining the dominant forcing mechanisms for ionosphere variability is important for prediction and mitigation of these threats. However, this is a challenging task due to the complexity of solar‐terrestrial coupling processes. Tidal oscillations (mostly 12 and 24‐hr periods) allow for a rough estimations of whether forcing from “above” or “below” dominates. The classical understanding is that 12‐hr oscillations propagate upwards from below while 24‐hr oscillations are forced at high altitudes. We analyze data from two radar systems and three global ionosphere models and show that the altitude structure of tidal oscillations is in fact more complex than classically assumed.
    Description: Key Points: Twenty‐day long EISCAT radar campaign shows a complex mixture of semidiurnal and diurnal tidal oscillations. Three global circulation models show similar tidal structuring and allow to determine the influence of different forcing mechanisms. Adaptive spectral filtering (ASF) technique allows robust fitting of tidal amplitudes and phases.
    Description: EISCAT
    Description: JSPS KAKENHI
    Description: DFG
    Description: https://doi.org/10.5281/zenodo.6817130
    Description: https://doi.org/10.5281/zenodo.7072141
    Keywords: ddc:538.7 ; ionsopheric transition region ; tidal oscillations ; EISCAT radar campaign
    Language: English
    Type: doc-type:article
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  • 2
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Macromolecules 1 (1968), S. 157-162 
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    International journal of fracture 2 (1966), S. 393-399 
    ISSN: 1573-2673
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Résumé Griffith a établi le critère d' énergie de fracture pour les matériaux fragiles fissurés. Ce critère d' énergie est équivalent au critère d' environnement de contrainte et de déformation pour les fractures fragiles comme indiqué par les solutions élastiques pour les solider fissurés. Pour une fracture quasi-fragile, c' est à dire dans le car oú de petites quantités de déformation plastiques à l' extrémité de la fissure précedent la fracture, le critère d' énergie est également équivalent au critère d'environnement de contrainte et de déformation. Un critère d' “engineering” pour des fractures ductiles, basé sur le concept d'environnement de contrainte et de déformation, suggére que, à la fracture, la dimension de la région de forte déformation à l' extrémité de la fissure est constante.
    Abstract: Zusammenfassung Griffith fand das Energiebruch Kriterium fuer sproedes Material. Fuer das Spannungsund Dehnungs Kriterium fuer sproede Brueche ist dieses Energie em fluss Kriterium gleichwertig, wie von der elastischen Loesung fuer sproede teste Koerper ersehen werden kana. Fuer fast sproede Brueche, dass heisst, in dem Falle wo geringe Mengen bildsamer Formgebung an der Bruchspitze dem Bruch vorangehen, ist das Energie Kriterium immernoch dem Spannungs- und Dehnungseinfluss Kriterium gleichwertig, Gegruendet an die Theorie des Spannungs- und Dehnungseinflusses, ein Engenieurs Kriterium fuer formbare Brueche, es wird angenommen, dass die Groesse eines stark gedehnten Bereiches konstant ist.
    Notes: Abstract The Griffith energy criterion is equivalent to a critical stress and strain environment criterion for brittle fractures. For quasi-brittle fracture, i. e. the case where small amounts of plastic deformation at the crack tip precedes fracture, the energy criterion is still equivalent to stress and strain environment criterion. Based on the concept of a critical stress and strain environment, it is proposed as an engineering criterion for ductile fracture, that at fracture the size of the highly strained region at crack tip is constant.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    International journal of fracture 5 (1969), S. 45-55 
    ISSN: 1573-2673
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Résumé Un modelé mécanique de la propagation des fractures de fatigue a été étudié. On suppose que la propagation provient l'accumulation des défauts en tête de la fissure durant la déformation alternée du matériau. On peut calculer la vitesse de propagation des fractures d'un matérial donné à l'aide de la loi de l'accumulation des défauts de Miner et de la loi de Manson et Coffin sur la fatigue en déformation alternée. On compare les valeurs calculées avec les résultats obtenus avec les aciers inoxydables 7075-T6 Al, 2024-T4 Al AM 350 et l'acier martensitique vieilli 18 Ni. La correlation entre les valeurs calculées et expérimentales est assez bonne. Les résultats obtenus montrent que la résistance d'un matériau à la propagation des fractures de fatigue depend de sa capacité à soutenir les déformations alternées, c'est-à-dire de sa ductilité en déformation cyclique.
    Abstract: Zusammenfassung Ein mechanisches Modell der Rißfortpflanzung in Ermüdung wurde untersucht. Es wird angenommen, daß Rißfortpflanzung durch einen akkumulierten Schädigungsprozeß, zufolge der Dehnungsschwingungen des Materials am Rißgrund, verursacht wird. Die Rißfortpflanzungsgeschwindigkeit cities Materials kann, mit Hilfe des Schädigungsgesetzes von Miner und des Manson-Coffin Gesetzes für Ermüdung durch Dehnungsschwingungen, berechnet werden. Die so errechneten Werte werden mit den experimentellen Ergebnissen für Aluminium Legierungen 7075-T6, 2024-T4, rostfreiem Stahl AM 350 und Marageing Stahl 18% Ni verglichen. Die Übereinstimmung zwischen experimentellen und errechneten Werten ist verhältnismßig gut. Die Ergebnisse zeigen, daß der Widerstand eines Werstoffes gegen Rißfortpflanzung in Ermüdung mit seiner Dehnungschwingungsfestigkeit, d.h. mit seinem dynamischen Dehnungsvermögen im Zusammenlrang steht.
    Notes: Abstract A mechanical model of fatigue crack propagation was studied. It is hypothesized that propagation is caused by cumulative damage due to strain cycling of the material at a crack tip. With Miner's cumulative damage law and Manson and Coffin's strain cycle fatigue: law, crack propagation rate of a material can be calculated. The calculated values are compared with data on 7075-T6 Al, 2024-T4 Al, AM 350 stainless steel, and 18 Ni maraging steel. The calculated and experimental values correlate reasonably well. The results indicate that fatigue crack propagation resistance of a material is related to its capability to sustain strain cycling, i.e. its cyclic ductility.
    Type of Medium: Electronic Resource
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  • 5
    Publication Date: 2023-06-13
    Description: Tidal wind oscillations in the high-latitude ionospheric dynamo/transition region can be in situ forced or propagate there from lower atmospheric layers. Investigating the complex mixing of tidal modes allows determining the solar, geomagnetic, and atmospheric impact on the transition region dynamics. In classical tidal theory at high latitudes, semidiurnal tides forced by UV and IR absorption in lower atmospheric regions propagate upwards and are the dominant tidal mode up to about 120 km. Above, diurnal modes forced in situ by EUV absorption and ion drag due to the polar plasma convection are assumed dominant. We analyze a 22-day-long measurement campaign with the EISCAT UHF incoherent scatter radar during September 2005. The beam-swinging experiment allows for obtaining neutral winds from 96 - 142 km altitude which are combined with simultaneous Kiruna meteor radar measurements. An Adaptive Spectral Filtering technique is applied to determine tidal amplitudes and phases. The zonal wind showed the expected transition from semidiurnal to diurnal oscillations at about 120 km. The meridional wind showed a more complex structure with dominant 12h oscillations below 110 km and above 130 km. General Circulation Model runs with different forcing settings are analyzed to determine the origin of these high-altitude semidiurnal oscillations. The measured asymmetry of tidal amplitudes in zonal and meridional winds is found in all investigated model runs. It is shown that at high latitudes, atmospheric tides do not influence semidiurnal oscillations above 120 km. The polar ion convection and EUV absorption both contribute to the observed high-altitude semidiurnal oscillations.
    Language: English
    Type: info:eu-repo/semantics/conferenceObject
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  • 6
    Publication Date: 2023-02-02
    Description: How the crust in the core of the Eastern Himalayan Syntaxis (EHS) deforms responding to the India-Asia collision remains ambiguous. Here we present the first high-resolution receiver functions image of crustal structure along a new NW-SE trending dense nodal array crossing the core of the EHS. Two sets of low velocity zones (LVZs) are clearly observed: one with a flat style beneath the western Lhasa terrane and Higher Himalaya at 18–20 km depth and the other with two west-dipping shapes below the western Yarlung-Zangbo suture within 10–30 km depth. These LVZs caused by partial melting and aqueous fluids are disconnected, impeding the formation of crustal flow. A discontinuous east-dipping intra-crustal discontinuity and a sharp Moho offset of 7 km under the Aniqiao-Motuo shear zone are identified, suggesting that the underthrusting of the Indian lower crust and pure shear mechanisms jointly dominate crustal deformation in the core of the EHS.
    Type: info:eu-repo/semantics/article
    Format: application/pdf
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  • 7
    Publication Date: 1968-03-01
    Print ISSN: 0024-9297
    Electronic ISSN: 1520-5835
    Topics: Chemistry and Pharmacology , Physics
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  • 8
    Publication Date: 1969-03-01
    Print ISSN: 0376-9429
    Electronic ISSN: 1573-2673
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by Springer
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  • 9
    Publication Date: 1966-06-01
    Print ISSN: 0376-9429
    Electronic ISSN: 1573-2673
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by Springer
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  • 10
    Publication Date: 1967-07-01
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
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