Laboratory investigations on fault plane induced tensile cracks     

Jan Kozák  Jan Šílený  Ludvík Waniek  Reviewer V. Červený 《Studia Geophysica et Geodaetica》1981,25(4):332-342

Summary Tensile cracks induced by stress concentration around a fault plane in physical models under uniaxial load were analyzed. The results characterizing the decisive role of the fault plane inclination to the the stress direction are presented. Two stages of tensile crack life were determined, i.e. the first, seismoactive stage, accompanied by seismic energy release and the second aseismic one characterized by low velocity of crack propagation. Results obtained seem to be relevant to a better understanding of the character and regime of actual seismoactive faults.  相似文献   

Anomalous behaviour of seismic waves at an interface between anisotropic media     

Jan Šílený  Reviewer V. Červený 《Studia Geophysica et Geodaetica》1981,25(2):152-159

Summary An account of possible anomalous effects in reflection and refraction of elastic waves at an interface between anisotropic media is presented. These effects are due to anisotropy and they cannot occur at an interface between isotropic media. The shape of the slowness surface (its local deviations from spherical symmetry) is the decisive factor for appearance of these effects. A numerical example of such anomalous behaviour of elastic waves at a free boundary of the crystal of spinel is presented.  相似文献   

Book reviews     

B. Valníček  Zdeněk Švestka 《Solar physics》1984,94(2):427-427

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Coronal interconnection of two active regions observed in 3.5–8.0 keV X-rays     

František Fárník  H. Frank Van Beek  Zdeněk Švestka 《Solar physics》1986,104(2):321-332

Using HXIS data, we have studied the further development of the coronal arch extending towards the SE above active region No. 17255 in November 1980. The arch, studied originally by vestka (1984) disappeared on 10 November (after pronounced revival), but since 9 November HXIS revealed another arch-like structure towards the SW. We have studied the development of this new structure which appeared to be most likely an arch interconnecting AR 17255 with AR 17251, located nearly 30° to the west. This interconnection revived many times during the following days with intensity varying with the activity in both active regions. We have estimated the physical characteristics in this coronal structure and compared them with observations of interconnecting loops made at lower energies by Skylab in 1973. The temperature (maximum values 7.5–14 × 10⁶ K) and the density (1.1–5.0 × 10⁹ cm^–3) are found to be higher than in the Skylab loops (a result that could be expected because the HXIS energy range was harder than that of Skylab) and similar to the values deduced for the earlier arch system extending to the SE. However, much shorter decay times of the brightness variations indicate the presence of conduction in contrast to the SE arch in which conduction was clearly inhibited. This supports the assumption that the SE and SW coronal structures were two different phenomena.Presently at Delft Institute of Technology, Landbergstraat 3, 2628 CE Delft, The Netherlands.  相似文献   

Preliminary study on the mineral magnetic properties of sediments from Kůlna Cave (Moravian Karst), Czech Republic     

P. Šroubek  J. F. Diehl  J. Kadlec  K. Valoch 《Studia Geophysica et Geodaetica》1996,40(3):301-312

Summary Magnetic property variations in marine, lacustrine and loess-paleosol sequences have proved to be useful proxies in climate change studies. However in order to correctly interpret the record of the magnetic property variations it is absolutely necessary to have a good understanding of the cause of the observed variations. Most of the ambiguity in loess-paleosol studies is in distinguishing the role of pedogenesis from other climatic factors. Studying the mineral magnetic properties of the protected cave sediments which have not undergone pedogenesis allows us to determine the degree to which detrital input is climatically driven. These results will help us better understand the variations observed in the surficial loess-paleosol sequences. This study reports mineral magnetic data collected from entrance facies sediments deposited during the early Wurmian glacial stage in the Kůlna Cave. The entrance facies sediments consist of loess-like silts with varying amount of talus. The magnetic susceptibility record from these sediments shows higher values in layers originating in colder climates which is different to that commonly observed in surficial loess deposits. Higher values of magnetic susceptibility in Kůlna sediments are probably due to higher concentrations of ferromagnetic minerals (magnetite and maghemite) and due to an increased proportion of superparamagnetic grains. The magnetic mineralogy and the grainsize distribution (grains larger than superparamagnetic) appear not to change throughout the studied profiles. Higher magnetic susceptibility accompanied by an increase in the superparamagnetic fraction observed in the sediments deposited during colder periods can be explained by an increased input from a pedogenic source when the vegetation cover was reduced and the erosion rate increased.  相似文献   

20th-CENTURY CHANGES OF TEMPERATURE IN THE MOUNTAIN REGIONS OF CENTRAL EUROPE     

RUDOLF O. WEBER  PETER TALKNER  INGEBORG AUER  REINHARD BÖHM  MARJANA GAJIĆ-ČAPKA  KSENIJA ZANINOVIĆ  RUDOLF BRÁZDIL  PAVEL FAŠKO 《Climatic change》1997,36(3-4):327-344

Daily maximum and minimum temperatures from 29 low-lying and mountain stations of 7 countries in Central Europe were analyzed. The analysis of the annual variation of diurnal temperature range helps to distinguish unique climatic characteristics of high and low altitude stations. A comparison of the time series of extreme daily temperatures as well as mean temperature shows a good agreement between the low-lying stations and the mountain stations. Many of the pronounced warm and cold periods are present in all time series and are therefore representative for the whole region. A linear trend analysis of the station data for the period 1901–1990 (19 stations) and 1951–1990 (all 29 stations) shows spatial patterns of similar changes in maximum and minimum daily temperatures and diurnal temperature range. Mountain stations show only small changes of the diurnal temperature range over the 1901–1990 period, whereas the low-lying stations in the western part of the Alps show a significant decrease of diurnal temperature range, caused by strong increase of the minimum temperature. For the shorter period 1951–1990, the diurnal temperature range decreases at the western low-lying stations, mainly in spring, whereas it remains roughly constant at the mountain stations. The decrease of diurnal temperature range is stronger in the western part than in the eastern part of the Alps.  相似文献   

Post-flare coronal arches observed with the SMM/XRP Flat Crystal Spectrometer     

Paul Hick  Zdeněk Švestka  Kermit L. Smith  Keith T. Strong 《Solar physics》1987,114(2):329-345

The phenomenon of post-flare coronal arches, initially discovered with the Hard X-Ray Imaging Spectrometer (HXIS), was investigated using observations made with the SMM Flat Crystal Spectrometer (FCS) on 20 through 23 January, 1985. Since these observations were made with a different type of instrument from HXIS, they provide independent information on the physical characteristics of the arch phenomenon and extend our knowledge to lower coronal temperatures.Conspicuous arch activity was observed after three flares and after a disturbance which could not be identified. (1) A dynamic flare starting on 20 January at 20: 39 UT was responsible for the formation of the primary arch structure. (2) An arch revival, showing characteristics very similar to those of the arch revivals observed with HXIS, took place after the dynamic flare starting on 21 January at 23: 50 UT. The most conspicious difference relates to the moving thermal disturbance observed very shortly after the onset of the parent flare, in particular to its propagation velocity. This difference in the arch revival is probably related to the different range of plasma temperatures covered by the FCS observations (3 × 10⁶ K through 6 × 10⁶ K) and the HXIS observations (>10⁷ K) and the consequently more important effects of radiative cooling in the FCS arch revival. (3) More arch activity was observed after a (possibly dynamic) flare starting at 03: 40 UT on 21 January and (4) after an unidentified event with estimated time of occurrence near 23: 00 UT on 22 January. Similar to the arch revival, this activity was primarily characterized by the energization of (i.e., input of energy to) a pre-existing arch structure. The activity after the unidentified event suggests the existence of a mode of arch activation which is different from the typical flare-associated revival and is characterized by the absence of significant activity at chromospheric levels.  相似文献   

Mass transfer and line profiles — WZ Sge     

Z. Šima  P. Hadrava 《Astrophysics and Space Science》1987,130(1-2):151-156

The calculation of a gas stream offers two modes of the stream. In any case the stream cannot be detected optically. The calculated line profiles caused by the disc are demonstrated.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986  相似文献   

ON THE POSSIBLE CHANGES OF THE SOLAR DIFFERENTIAL ROTATION DURING THE ACTIVITY CYCLE DETERMINED USING MICROWAVE LOW-BRIGHTNESS-TEMPERATURE REGIONS AND Hα FILAMENTS AS TRACERS     

BRAJŠA  R.  RUŽDJAK  V.  VRŠNAK  B.  POHJOLAINEN  S.  URPO  S.  SCHROLL  A.  WÖHL  H. 《Solar physics》1997,171(1):1-34

The solar rotation rate obtained using the microwave Low-brightness-Temperature Regions (LTRs) as tracers in the heliographic range ± 55° from the years 1979–1980, 1981–1982, 1987–1988, and 1989–1991 varied from 3% to 4% in medium latitudes, and below 1% at the equator. Using H filaments as tracers at higher latitudes from the years 1979, 1980, 1982, 1984, and 1987, the solar rotation rate variation was between 2% and 8%. This represents an upper limit on the rotation rate variation during the solar activity cycle. Such changes could be caused by short-lived, large-scale velocity patterns on the solar surface. The Sun revealed a higher rotation rate on the average during the maxima of the solar activity cycles 21 and 22, i.e., in the periods 1979–1980 and 1989–1991, respectively, which differs from the rotation rates (lower on the average) in some years, 1981–1982 and 1987–1988, between the activity maximum and minimum (LTR data). Simultaneous comparison of rotation rates from LTRs and H filament tracings was possible in very limited time intervals and latitude bands only, and no systematic relationship was found, although the rotation rates determined by LTRs were mostly smaller than the rotation rates determined by H filaments. The errors obtained by applying different fitting procedures of the LTR data were analyzed, as well as the influence of the height correction. Finally, the north–south asymmetry in the rotation rate investigated by LTRs indicates that the southern solar hemisphere rotated slower in the periods under consideration, the difference being about 1%. The reliability of all obtained results is discussed and a comparison with other related studies was performed.  相似文献   

Large-Scale Active Coronal Phenomena in YOHKOH SXT Images. III. Enhanced Post-Flare Streamer     

Švestka  Zdeněk  Fárník  František  Hick  Paul  Hudson  Hugh S.  Uchida  Yutaka 《Solar physics》1997,176(2):355-371

We demonstrate several events where an eruptive flare close to the limb gave rise to a transient coronal streamer visible in X-rays in Yohkoh SXT images, and analyze one of these events, on 28–29 October 1992, in detail. A coronal helmet streamer began to appear 2 hours after the flare, high above rising post-flare loops; the streamer became progressively narrower, reaching its minimum width 7–12 hours after the flare, and widened again thereafter, until it eventually disappeared. Several other events behaved in a similar way. We suggest that the minimum width indicates the time when the streamer became fully developed. All the time the temperature in the helmet streamer structure was decreasing, which can explain the subsequent fictitious widening of the X-ray streamer. It is suggested that we may see here two systems of reconnection on widely different altitudes, one giving rise to the post-flare loops while the other creates (or re-forms) the coronal helmet streamer. A similar interpretation was suggested in 1990 by Kopp and Polettofor post-flare giant arches observed on board the SMM; indeed, there are some similarities between these post-flare helmet streamers and giant arches and, with the low spatial resolution of SMM instruments, it is possible that some helmet streamers could have been considered to be a kind of a giant arch.  相似文献