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991.
992.
B. Růžek P. Hrubcová M. Novotný A. Špičák O. Karousová 《Studia Geophysica et Geodaetica》2007,51(1):141-164
A series of kinematic inversions based on robust non-linear optimization approach were performed using travel time data from
a series of seismic refraction experiments: CELEBRATION 2000, ALP 2002 and SUDETES 2003. These experiments were performed
in Central Europe from 2000 to 2003. Data from 8 profiles (CEL09, CEL10, Alp01, S01, S02, S03, S04 and S05) were processed
in this study. The goal of this work was to find seismic velocity models yielding travel times consistent with observed data.
Optimum 2D inhomogeneous isotropic P-wave velocity models were computed. We have developed and used a specialized two-step
inverse procedure. In the first “parametric” step, the velocity model contains interfaces whose shapes are defined by a number
of parameters. The velocity along each interface is supposed to be constant but may be different along the upper and lower
side of the interface. Linear vertical interpolation is used for points in between interfaces. All parameters are searched
for using robust non-linear optimization (Differential Evolution algorithm). Rays are continuously traced by the bending technique.
In the second “tomographic” step, small-scale velocity perturbations are introduced in a dense grid covering the currently
obtained velocity model. Rays are fixed in this step. Final velocity models yield travel time residuals comparable to typical
picking errors (RMS ∼ 0.1 s).
As a result, depth-velocity cross-sections of P waves along all processed profiles are obtained. The depth range of the models
is 35–50 km, the velocity varies in the range 3.5–8.2 km/s. Lowest velocities are detected in near-surface depth sections
crossing sedimentary formations. The middle crust is generally more homogeneous and has typical P wave velocity around 6 km/s.
Surprisingly the lower crust is less homogeneous and the computed velocity is in the range 6.5–7.5 km/s. The MOHO is detected
in the depth ≈30–45 km. 相似文献
993.
P. Šauli Z. Mošna J. Boška D. Kouba J. Laštovička D. Altadill 《Studia Geophysica et Geodaetica》2007,51(3):449-459
The changing state of the ionosphere is generally monitored by networks of vertical ionosondes that provide us with regular
ionospheric sounding. Many ionospheric applications require determination of the true-height electron density profiles. Therefore,
ionograms must be further inverted into real-height electron density profiles. The paper presents the comparison study of
the true-height electron density profiles inverted from ionograms using two different methods POLAN (Titheridge, 1985) and
NHPC (Huang and Reinish, 1996; Reinish et al., 2005), widely used by the ionospheric research community. Our results show
significant systematic differences between electron density profiles calculated by these two inversion methods.
pkn@ufa.cas.cz 相似文献
994.
Data concerning solar energetic events, published in 1996–2004 by the USAF/NOAA in the form of daily reports, have been collected.
The analysis of the particular event types indicates that the degree of their geoeffectiveness depends on their size and on
their solar disc location. The mere information that a solar X-flare (XRA) event or a Long Duration XRA Event (LDE) has occurred
on the solar disc is insufficient to produce a relevant forecast of geomagnetic disturbances. The probability increases if
the XRA is of class X which has occurred on the solar disk in central region (30 °E, 30 °W; 30 °S, 30 °N). XRAs associated
with metric type II and IV radio bursts (RSP II and RSP IV), which occurred on the solar disc in this region will very probably
cause a geomagnetic disturbance not only if X class are involved, but also M class and B–C class. The Disappearance of Solar
Filament (DSF) data cannot be used in forecasting geomagnetic disturbances. The geoeffective and nongeoeffective DSFs are
too disproportional.
jboch@ig.cas.cz
fridrich@geomag.sk 相似文献
995.
A forecasting scheme of geomagnetic activity is presented, based on the analysis of the geoeffectiveness of X-ray flares,
accompanied by Type II and/or Type IV radio bursts (RSP) observed on the solar disc in the years 1996–2004. The neural network
was used to construct this scheme enabling us to determine the probability, with which flares will be followed by a geomagnetic
response of a particular intensity. The successfulness of forecasts produced after the fact depended on the flare class and
on the combination of radio-burst types. In the case of RSP IV, 58% of the geomagnetic responses of X-ray flares of at least
B class were successful. If only RSP II was observed, the forecast was successful only for flares of the X class (67% of successful
forecasts). In the second step, a strong geomagnetic response was correctly forecast after geoeffective flares in 58% of the
cases. The results are in a good agreement with recent papers based on physical modelling.
fridrich@geomag.sk
ph@ig.cas.cz, jboch@ig.cas.cz 相似文献
996.
The seasonal variation of gravity wave activity at altitudes around 95 km is investigated using digital measurements of low-frequency nighttime radiowave absorption at Prhonice (50°N, 15°E) between 1989 and 1993. The analysis of 5 years of data allows two conclusions to be drawn: (1) under high solar activity conditions, there is no clearly detectable seasonal variation of gravity wave activity; (2) under medium solar activity conditions (1992, 1993), there is a tendency to a pronounced summer maximum. 相似文献
997.
998.
Jozef Klačka 《Earth, Moon, and Planets》1992,56(1):47-52
The dependence of the cumulative number of numbered asteroids (up to 3720) on their absolute magnitude is investigated. The differential mass index k is derived from these relations for fainter asteroids. A steeper slope (2.2 < k < 2.4) is found in the four most populous asteroid familes (Flora, Koronis, Eos and Themis) and a flatter slope (1.3 < k < 1.6) for non-family asteroids. This indicates that there are two different asteroid populations in the asteorid belt. Total masses of the asteroid families may be greater than it is commonly accepted. 相似文献
999.
1000.
Catherine Leyx J. Cornelis Van Miltenburg Christian Chopin Lado Cemič 《Physics and Chemistry of Minerals》2005,32(1):13-18
The low-temperature heat capacity of -Mg2PO4OH was measured between 10 and 400 K by adiabatic calorimetry. No phase transition was observed over this temperature range. A relative enthalpy increment of 22,119 J mol–1 and an absolute entropy value of 127.13±0.25 J mol–1 K–1 at 298.15 K are derived from the results. The low-temperature heat-capacity data are compared with the DSC data obtained from 143 K to 775 K and show marginal differences in the common temperature range. The latter data are fitted by the polynomial
which allows extrapolation to high temperatures.Software information: WINDOWS operating system, WORD word processing, SigmaPlot diagrams exported in tiff format. 相似文献