Effect of the lower ionosphere on electromagnetic disturbances with periods corresponding to micropulsations     

Josef Bochníček 《Studia Geophysica et Geodaetica》1969,13(1):60-75

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Besonderheiten der Windstruktur auf Einem Kegelgipfel     

František Rein 《Studia Geophysica et Geodaetica》1962,6(3):309-311

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Buchbesprechungen     

Steinhauser  F.  Reuter  H.  Burkard  O.  Konček  N.  Drimmel  J.  Pichler  H. 《Meteorology and Atmospheric Physics》1962,12(4):544-562

Ohne Zusammenfassung  相似文献   

The Friedmann universe and the world potential     

Pavel Voráček 《Astrophysics and Space Science》1981,74(2):463-474

In Section 1 of the paper the energy equation of the Friedmann universe, when matter dominates over radiation, is discussed. It is known that the value of the world potential is constant everywhere in the Universe, despite the pulsation motion of the Universe or a possible transformation of pulsation energy into matter or vice versa. The condition for the Universe being closed is deduced. Furthermore, the possibility to define the mass-energy of the Universe is discussed; and the conclusion is arrived at that the mass-energy of the Universe relative to an observer in the non-metric space outside the Universe is equal to zero; i.e. the Universe originated as a vacuum fluctuation. Finally, the view-point of an external observer is described. Such an observer can claim that our closed Universe is a black hole in a non-metric empty space. Besides, the differences between such a black hole and the astrophysical black holes are indicated.In Section 2 the origin of the gravitational force retarding the expansion is discussed, using the properties of the relativistic gravitational potential. In contradiction to Section 1, the view-point of an inner observer (inside the Universe) is used here. It is concluded that the boundary of the closed Universe is an unlocalizable potential barrier.In Section 3 of the paper the apparent discrepancy between Mach's principle and the general theory of relativity is resolved. The solution is based on the fact that, for the Euclidean open universe, the concept of mass is related to the potential of the background equal to –1, but the concept of the mass-energy is related to the zero-potential of the non-metric background. Because the universe is open and a potential barrier (a boundary of the universe) can be localized-i.e. is geometrically existing — by solution of the field equation, we have to refer to the background with zero-potential. The principal idea of the solution is then that the zero-density means the density of mass-energy, when simultaneously the mass density is equal to the critical value for which the Robertson-Walker metric becomes the Euclidean metric of the Minkowski (i.e., flat) space-time. Further a generalization of Newton's law of inertia is formulated, and the properties of nullgeodesics are touched upon. As a conclusion it is stated that this paper and the two previous ones (see Voráek, 1979a, b)de facto express Mach's principle.  相似文献   

Твердый налет в зимнее время на милешовке     

František Rein 《Studia Geophysica et Geodaetica》1961,5(3):256-263

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Origin and orientation of microporosity in eclogites of different microstructure studied by ultrasound and microfabric analysis     

M. Machek  P. &#x;pa ek  S. Ulrich  F. Heidelbach 《Engineering Geology》2007,89(3-4):266-277

This work contributes to the experimental investigations of the origin and 3-D orientation of micropores in low porosity crystalline rocks. The origin and spatial orientation of microporosity in two eclogites with different microstructures were studied by 1) quantitative and qualitative microstructural analysis of grains and grain boundaries, 2) measurement of lattice preferred orientation using the SEM-EBSD method and 3) experimental measurement of velocity of elastic P-waves in spherical samples in 132 directions under confining pressures up to 400 MPa. Results show good correlation between the elastic properties and the orientation of grain boundaries and cleavage planes in clinopyroxene. The magnitude and anisotropy of velocity change with pressure shows that microporosity in the fine-grained sample is relatively large and strongly preferentially oriented, whereas it is significantly lower and less preferentially oriented in the coarse-grained sample. Seeing that the lattice preferred orientation of clinopyroxene is similar in both samples we can deduce from velocity changes that the grain size of the rock forming minerals controls the amount of microporosity. Also, the orientation of microporosity depends mostly on preferred orientation of grain boundaries and somewhat less on the orientation of cleavage planes. Grain boundaries are therefore the most important contributors to the bulk microporosity in the studied rocks.  相似文献   

Laboratory Approach to the Study of Elastic Anisotropy on Rock Samples     

Z. Pros  T. Lokajíček  K. Klíma 《Pure and Applied Geophysics》1998,151(2-4):619-629

—The experimental approach (hardware and software) to the study of the elastic an isotropy of rocks on spherical samples under hydrostatic pressure up to 400 MPa is discussed. A substantial innovation of the existing measuring system and processing methods enabled us to make a detailed investigation and evaluation of the kinematic as well as dynamic parameters of elastic waves propagating through anisotropic media. The innovation is based on digital recording of the wave pattern with a high sampling density of both time and amplitude. Several options and results obtained with the innovated laboratory equipment are presented.  相似文献   

Evidence of Magnetic Field Reconnection in the Hα Eruptive Prominence on 18 september 1995     

Kotrč  P.  Karlický  M.  Šimberová  S.  KnÍŽek  M.  Varady  M. 《Solar physics》1998,182(2):393-409

In this paper we present a detailed study of a violent evolution of the 18 September 1995 eruptive prominence observed by the H telescope and the Multichannel Optical Flare Spectrograph in Ondejov. The fast changes of the prominence structure started immediately after a weak radio burst at 3 GHz. This circumstance shows the presence of non-thermal processes. In the later phase of the prominence evolution a comparison of the H filtergrams with the Yohkoh Soft X-ray Telescope pictures was made. For a search of fine structures in the H images, an image processing technique was used. A detailed analysis of observations indicates magnetic field line reconnection, mainly in space below the rising H prominence. These reconnection processes are manifested not only by structural changes of the H prominence and X-ray loops but also by the character of Doppler velocities. Evidence of splitting and rotation was found in the H spectrum formed close to the reconnection space, and the typical velocities of such plasma movement were evaluated. We estimated amplitudes of rotational velocities, giving evidence about the rearrangement of helical structures during the process of the eruptive prominence activation. In the conclusion we discuss some implications of our results.  相似文献   

Performance of three types of Stokes's kernel in the combined solution for the geoid   总被引：8，自引：6，他引：2  

P. Vaníček  W. E. Featherstone 《Journal of Geodesy》1998,72(12):684-697

When regional gravity data are used to compute a gravimetric geoid in conjunction with a geopotential model, it is sometimes implied that the terrestrial gravity data correct any erroneous wavelengths present in the geopotential model. This assertion is investigated. The propagation of errors from the low-frequency terrestrial gravity field into the geoid is derived for the spherical Stokes integral, the spheroidal Stokes integral and the Molodensky-modified spheroidal Stokes integral. It is shown that error-free terrestrial gravity data, if used in a spherical cap of limited extent, cannot completely correct the geopotential model. Using a standard norm, it is shown that the spheroidal and Molodensky-modified integration kernels offer a preferable approach. This is because they can filter out a large amount of the low-frequency errors expected to exist in terrestrial gravity anomalies and thus rely more on the low-frequency geopotential model, which currently offers the best source of this information. Received: 11 August 1997 / Accepted: 18 August 1998  相似文献   

Inelastic spectra for infilled reinforced concrete frames     

Matja Dol&#x;ek  Peter Fajfar 《地震工程与结构动力学》2004,33(15):1395-1416

In two companion papers a simplified non‐linear analysis procedure for infilled reinforced concrete frames is introduced. In this paper a simple relation between strength reduction factor, ductility and period (R–µ–T relation) is presented. It is intended to be used for the determination of inelastic displacement ratios and of inelastic spectra in conjunction with idealized elastic spectra. The R–µ–T relation was developed from results of an extensive parametric study employing a SDOF mathematical model composed of structural elements representing the frame and infill. The structural parameters, used in the proposed R–µ–T relation, in addition to the parameters used in a usual (e.g. elasto‐plastic) system, are ductility at the beginning of strength degradation, and the reduction of strength after the failure of the infills. Formulae depend also on the corner periods of the elastic spectrum. The proposed equations were validated by comparing results in terms of the reduction factors, inelastic displacement ratios, and inelastic spectra in the acceleration–displacement format, with those obtained by non‐linear dynamic analyses for three sets of recorded and semi‐artificial ground motions. A new approach was used for generating semi‐artificial ground motions compatible with the target spectrum. This approach preserves the basic characteristics of individual ground motions, whereas the mean spectrum of the whole ground motion set fits the target spectrum excellently. In the parametric study, the R–µ–T relation was determined by assuming a constant reduction factor, while the corresponding ductility was calculated for different ground motions. The mean values proved to be noticeably different from the mean values determined based on a constant ductility approach, while the median values determined by the different procedures were between the two means. The approach employed in the study yields a R–µ–T relation which is conservative both for design and performance assessment (compared with a relation based on median values). Copyright © 2004 John Wiley & Sons, Ltd.  相似文献