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  • 1
    ISSN: 1619-6937
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Description / Table of Contents: Zusammenfassung Es wird ein Anfangswertproblem gelöst für die kombinierten Einflüsse einer freien und erzwungenen Konvektion in einer rotierenden, hydromagnetischen Strömung eines zähen Mediums unter dem Einfluß eines gleichförmigen magnetischen Feldes. Die hydromagnetische Strömung wird erzeugt in dem gleichförmig rotierenden Medium zwischen zwei festen thermisch isolierten, parallelen Platten durch kleine longitudinale Oszillationen der unteren Platte. Zusätzlich werden die Platten auf einem konstanten Temperaturgradienten in Plattenebene gehalten. Die exakten Lösungen für das Geschwindigkeitsfeld und die Temperaturverteilung werden durch Laplace-Transformation und die Residuenmethode gewonnen. Es wird gezeigt, daß die Lösungen aus einem stationären und einem instationären Anteil bestehen. Die Abklingzeit für den instationären Anteil wird ausführlich erörtert. Der stationäre Anteil besteht aus einer Grenzschicht in Plattennähe und einer Innenströmung. Die physikalische Bedeutung der Lösungen und die Struktur der an den Platten gebildeten Grenzschichten wird besprochen. Die stationäre Lösung für Geschwindigkeit, Temperatur und Schubspannung wird numerisch gegeben und der Einfluß der Grashof-Zahl und der Plattenfrequenz diskutiert.
    Notes: Summary An initial value investigation is made of the combined effects of the free and forced convection in rotating hydromagnetic viscous fluid flows under the action of a uniform transverse magnetic field. The hydromagnetic flow is generated in the uniformly rotating fluid bounded between two rigid non-conducting paralled plates by small non-torsional oscillations of the lower plate, and in addition, the plates are maintained at a constant temperature gradient in a direction parallel to the plane of the plates. The exact solutions of the velocity field and the temperature distribution are obtained by the Laplace transform method combined with the theory of residues. It is shown that the solutions consists of the steady-state and the transient components. The time required for the transient effect to decay is discussed in detail, and the ultimate steady-state is shown to be composed of boundary layers on the plates and an interior flow. Attention is focused upon the physical nature of the solutions, and the structure of the various kinds of boundary layers formed on the plates. The final steady-state velocity, temperature and shear stresses are numerically discussed for different values of the Grashof number and frequency of the plate.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Acta mechanica 39 (1981), S. 303-309 
    ISSN: 1619-6937
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 3
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A 54.95-MHz coherent backscatter radar, an ionosonde and the magnetometer located at Trivandrum in India (8.5○N, 77○E, 0.5○N dip angle) recorded large-amplitude ionospheric fluctuations and magnetic field fluctuations associated with a Pc5 micropulsation event, which occurred during an intense magnetic storm on 24 March 1991 (Ap=161). Simultaneous 100-nT-level fluctuations are also observed in the H-component at Brorfelde, Denmark (55.6○N gm) and at Narsarsuaq, Greenland (70.6○N gm). Our study of the above observations shows that the E-W electric field fluctuations in the E- and F-regions and the magnetic field fluctuations at Thumba are dominated by a near-sinusoidal oscillation of 10 min during 1730–1900 IST (1200-1330 UT), the amplitude of the electric field oscillation in the equatorial electrojet (EEJ) is 0.1-0.25 mV m−1 and it increases with height, while it is about 1.0 mV m−1 in the F-region, the ground-level H-component oscillation can be accounted for by the ionospheric current oscillation generated by the observed electric field oscillation in the EEJ and the H-component oscillations at Trivandrum and Brorfelde are in phase with each other. The observations are interpreted in terms of a compressional cavity mode resonance in the inner magnetosphere and the associated ionospheric electric field penetrating from high latitudes to the magnetic equator.
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  • 4
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The systematic time differences observed in the onset of postsunset VHF scintillations recorded simultaneously at Ujjain (Geogr. lat. 23.2○N, Geogr. long. 75.6○E) and Bhopal (Geogr. lat. 23.2○N, Geogr. long. 77.6○E), situated at the peak of the anomaly crest in the Indian region, have been analysed to determine the zonal drifts of scintillation-producing irregularities. The method is based on the assumption that the horizontal movement of irregularities does not change while crossing the F-region cross-over points of these stations. The calculated velocities of irregularities indicate an eastward drift decreasing from about 180 m s−1 to 55 m s−1 during the course of night. In the premidnight period, the drifts are reduced under the magnetically disturbed conditions. The average east-west extension of irregularites is found to be in the range of 200–500 km.
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  • 5
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract In order to investigate the causal relationship between magnetic storms and substorms, variations of the mid-latitude geomagnetic indices, ASY (asymmetric part) and SYM (symmetric part), at substorm onsets are examined. Substorm onsets are defined by three different phenomena; (1) a rapid increase in the mid-latitude asymmetric-disturbance indices, ASY-D and ASY-H, with a shape of so-called ‘mid-latitude positive bay’; (2) a sharp decrease in the AL index; (3) an onset of Pi2 geomagnetic pulsation. The positive bays are selected using eye inspection and a pattern-matching technique. The 1-min-resolution SYM-H index, which is essentially the same as the hourly Dst index except in terms of the time resolution, does not show any statistically significant development after the onset of substorms; it tends to decay after the onset rather than to develop. It is suggested by a simple model calculation that the decay of the magnetospheric tail current after substorm onset is responsible for the decay of the Dst field. The relation between the IMF southward turning and the development of the Dst field is reexamined. The results support the idea that the geomagnetic storms and substorms are independent processes; that is, the ring-current development is not the result of the frequent occurrence of substorms, but that of enhanced convection caused by the large southward IMF. A substorm is the process of energy dissipation in the magnetosphere, and its contribution to the storm-time ring-current formation seems to be negligible. The decay of the Dst field after a substorm onset is explained by a magnetospheric energy theorem.
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  • 6
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 592-593 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Photoluminescence (PL) spectra of electron beam evaporated (ZnxCd1−x)3P2 thin films with composition (x) equal to 0.0, 0.2, 0.4, 0.5, 0.8, and 1.0 have been recorded at 100 K. The radiative transitions associated with the different PL peaks are correlated considering the distribution of native defects which act either as acceptor (A)- or donor (D)-like centers. In the case of (Zn0.5Cd0.5)3P2 films, which showed some satellite structure, the emission at 0.92 eV is related to the DA pairs (associated phosphorous interstitials and vacancies) with the distance of separation estimated in the range of 10–30 A(ring).
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  • 7
    ISSN: 1619-6937
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary The influence of Hall currents on the free and forced convective flow of a viscous rotating fluid between two horizontal plates is analysed. An exact solution for the velocity and temperature have been obtained. the effects of Hall currents on the velocity, the temperature and shear stress are discussed analytically and graphically.
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 28 (1987), S. 1473-1476 
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: A plausibility argument presented by the first two authors in an earlier paper [J. Math. Phys. 26, 3042 (1985)] concerning the existence of partially invariant solutions for some equations of the Fokker–Planck type is made precise by the explicit construction of one such solution. In the process a substantial simplification of Ovsiannikov's method for finding partially invariant solutions is achieved. In addition, the class of partially invariant solutions obtained by Ovsiannikov for the equations of transonic flow of a gas is enlarged.
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  • 9
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Long series of simultaneous VHF scintillation observations at two stations situated in near magnetic east-west direction in the vicinity of the dip equator in the Indian region have been employed to investigate the night-time ionospheric plasma zonal drifts. The drifts are found to be predominantly easterly. On comparing the magnitudes of the drifts with those results derived earlier by HF fading technique, monitoring signals from two satellites at a station and spaced receiver experiment, their associations with the season and the degree of solar activity are discussed. On a broader scale, the annual mean sunspot number is shown to have a direct control on the derived drift, the positive relationship even on day to day basis with the solar flux is established. However, the relationship, as understood by the slope of the best fit line, in the Indian region (0.27) is found to be weaker when compared with the similar slope (0.45) in the American sector. There appears to be no geomagnetic activity control on the estimated drifts.
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  • 10
    Electronic Resource
    Electronic Resource
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 46 (1990), S. 627-629 
    ISSN: 1600-5759
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
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