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1.
James R. Wait 《Pure and Applied Geophysics》1957,37(1):103-115
Summary The space between the earth and the ionosphere is considered as a wave-guide with sharply bounded walls. Employing a representation in terms of spherical wave functions of complex order, the field of a vertical dipole source is calculated for very low frequencies. It is shown that the dominant mode for 16 kc is of order one and not zero as has been commonly supposed. Good agreement is obtained with the experimental results ofJ. Heritage.Paper presented at «Colloque International sur la propagation des Ondes Radio électriques» Paris, September 1956. 相似文献
2.
Summary The electromagnetic mode characteristics for the earthcrust waveguide are considered. The formulation allows for any depth-conductivity profile, but the specific results are only for a homogeneous sub-surface waveguide region with a finitely conducting lower layer and a perfectly conducting upper layer. Attenuation rates of the order of 1 dB/km are possible for operating frequencies of 20 kHz or lower if the crystalline rock in the waveguide has conductivities less than 10–6 mhos per meter. 相似文献
3.
Summary The reflection and transmission of a transient plane wave by an ionosphere with a linear electron density profile and constant collision frequency are calculated. The exact frequency domain solution is inverted numerically, and the resultant reflected and transmitted waveforms are found to satisfy causality. A linearly varying, nondispersive dielectric half-space is also considered, but the nonphysical nature of the model causes the reflected waveform to be noncausal. Using convolution the waveforms for a step modulated sinusoid excitation are also obtained from the impulse response of the ionosphere. The results provide insight into the physical mechanism involved in the ionospheric propagation of HF electromagnetic pulsed signals. 相似文献
4.
Summary The subsurface electric fields of a current-carrying cable are examined for both steady-state and transient situations. Closed form expressions are obtained for two of the electric field components, and a numerical integration is used to obtain the third component. Waveforms for a stepfunction current excitation are displayed. The results have possible application to pulsed downlink communication in mine rescue operations. 相似文献
5.
Summary Treating the ionosphere as a sharply bounded ionized medium, sky wave field intensities are calculated by geometrical-optical methods for very low radio frequencies. The reflection coefficients are discussed in some detail and the numerical data are compared with experiment. 相似文献
6.
G. R. Wait 《Meteorology and Atmospheric Physics》1950,3(1-2):70-76
Summary The electric current passing vertically through thunderstorms has been measured above the thunderheads with apparatus mounted on a B-29 airplane. The direction of the resulting current, in all cases, was such as to maintain the negative charge found over the fair-weather region of the earth. The average magnitude of the current per storm was one ampere, an amount required of the average storm if the fair-weather charge is to be maintained through thunderstorm activity. Other results obtained are summarized at the end of the article.
With 3 figures.
Dedicated to Professor Dr.H. Benndorf on the occasion of his eightieth birthday. 相似文献
Zusammenfassung Der elektrische Strom, der vertikal durch Gewitter fließt, wurde oberhalb der Gewitterwolken mit Apparaten gemessen, die auf einem B-29-Flugzeug montiert waren. Der resultierende Strom war in allen Fällen so gerichtet, daß er die negative Ladung über dem Schönwettergebiet der Erde zu erhalten sucht. Die mittlere Stromstärke pro Gewitter betrug 1 Amp., welcher Durchschnittsbetrag gerade erforderlich ist, um die Schönwetterladung durch Gewittertätigkeit aufrechtzuerhalten. Weitere Ergebnisse sind am Ende des Aufsatzes zusammengefaßt.
Résumé On a mesuré à l'aide d'appareils montés sur un avion B-29 le courant électrique vertical issu des nuages orageux, au-dessus de ceux-ci. La direction du courant résultant était toujours telle qu'il tendait à maintenir la charge négative au-dessus de la région de beau temps de la terre. L'intensité moyenne par orage était de un ampère, valeur précisément nécessaire pour maintenir la charge de beau temps par l'activité orageuse. D'autres résultats sont résumés à la fin de l'article.
With 3 figures.
Dedicated to Professor Dr.H. Benndorf on the occasion of his eightieth birthday. 相似文献
7.
This paper presents real-time monitoring data and analysis results of the non-stationary vibrations of an operational wind turbine. The advanced time-frequency spectrum analysis reveals varied non-stationary vibrations with timevarying frequencies, which are correlated with certain system natural modes characterized by finite element analysis. Under the effects of strong wind load, the wind turbine system exhibits certain resonances due to blade passing excitations. The system also exhibits certain instabilities due to the coupling of the tower bending modes and blade flapwise mode with blade passing excitations under the variation of wind speed. An analytical model is used to elaborate the non-stationary and instability phenomena observed in experimental results. The properties of the nonlinear instabilities are evaluated by using Lyapunov exponent estimation. 相似文献
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An analytical formulation is developed for the resultant electromagnetic field of an oscillating vertical magnetic dipole located over a thin conductive sheet of infinite extent. The sheet is characterized by a conductivity-thickness product or conductance d that may be a function of the horizontal coordinates. The system of integral equations arising in the general formulation is simplified greatly when azimuthal symmetry prevails. Numerical results for a Gaussian variation of d in the radial direction are presented for the case of a symmetrically located source. These results are for the fields at the level of the source dipole over the conductive sheet. It is shown that the quadrature response of the sheet is enhanced when there is rapid variation of the conductance. The null in the resultant wave tilt is also found to be shifted toward the direction of increasing conductance. 相似文献
10.
The relevant potential theory is given for a current point source in the presence of a conductive slab embedded in a homogeneous host region of infinite extent. The thin sheet representation is obtained from the exact integral formulation by a simple mathematical limit process. The same result is also deduced directly at the outset by applying a thin sheet boundary condition. The apparent resistivity for a two electrode array is then computed for the case where the bore hole intersects the thin sheet at right angles. The corresponding results for the dilution factor, relevant to the induced polarization response, are also obtained. It is shown that the apparent resistivity and the dilution factor are constant when the potential and the current electrode straddle the sheet but there is a characteristic decrease as the electrodes move away from the sheet. 相似文献