Energy balance of simple elastodynamic sources

Complete relations are derived for energy and energy flux of elastic waves generated by an isotropic and double-couple source in a perfectly elastic, homogeneous, isotropic, and unbounded medium. In the energy balance of elastodynamic sources near-field waves play an essential role, transforming static energy into wave energy, andvice versa. For explosive and dislocation sources, the sources surface radiates a positive wave energy that is partially distributed to the medium transforming into static energy. For implosive and antidislocation sources, the source surface generates elastic waves, but it does not necessarily imply that it also radiates a positive wave energy. The energy transported by waves can originate in gradual transformation of the static-to-wave energy during propagation of waves through a stressed medium.On leave from Geophysical Institute, Czech Academy of Sciences, Boní II/1401, 41 31, Praha 4 Czech Republic     

Dynamics of the plasmasphere in the dusk sector as observed in the outer ionosphere

Summary Direct measurements of the thermal plasma parameters in the topside ionosphere reveal variations of the plasmasphere boundary in the dusk sector. The ACTIVE satellite's near-polar orbits at altitudes of 500 – 1800 km around winter solstice 1989 were used to study the bulge region of the plasmasphere during intervals with different levels of geomagnetic agitation. The narrow, sharply defined trough in electron concentration corresponding to the plasmapause under quiet conditions situated at L = 6 – 7 moved to lower L-values with increasing geomagnetic activity. This narrow trough can be found in all main ion constituents. During periods of moderate geomagnetic activity, following the onset of a weak magnetic storm, a portion of the plasmaspheric bulge region was separated from the main plasmaspheric body. This can be seen in the outer ionosphere as an inner narrow trough at lower L-value. Troughs in light ions need no longer coincide with this in electron concentration. He⁺ is the most sensitive constituent reflecting the dusk sector plasmaspheric situation at this altitude.Dedicated to the Memory of Professor Karel P     

Ab initio calculated electron densities for tetrahedral sheet [H2Si2O5]∞ in phyllosilicates

Periodic ab initio Hartree-Fock LCAO calculations have been carried out on the two dimensional sheet of SiO₄ tetrahedra, representing one of the basic constituting units of layer silicates, using Huzinaga's DZP basis sets. The influence of the basis set on the chemical bonding picture is characterized by Mulliken atomic charges and by electron density maps. Silicon atomic charges +1.6 ¦e¦ are more realistic than those +2.4 ¦e¦ reported for smaller basis sets. The silicon d orbital population is found to be 0.6 in close agreement with molecular data. Electron density maps indicate the absence of charge density in the center of the ditrigonal cavity. The charge buildup of nonbonding basal oxygen orbitals is directed mainly downwards perpendicular to the sheet plane.     

Geomagnetic activity as a possible cause of changes in the middle atmosphere and troposphere; observations made in Prague in the years 1932–1987

Summary A possible relation between the 10-day, 1-month, and 2-month geomagnetic as well as solar activity, characterized by Kp and Wolf's number R, and temperatures measured at the Prague-Klementinum meteorological station in January–February of the years 1932–1987 was sought. It was found that:1) Kp correlates with the temperature in Prague better than Wolf's number R.2) If the QBO phase is taken into account, the correlations improve.3) Even if the correlations improves with increasing length of the subintervals into which the individual winter periods (January-February) were derived, their statistical significance declines.     

Fossil carotenoids and paleolimnology of meromictic Mahoney Lake,British Columbia,Canada

Vertical distribution of fossil carotenoids in a sediment core from meromictic Mahoney Lake was studied. Besides okenone and demethylated okenone, lutein and zeaxanthin and-carotene isomers were identified. No carotenoids typical for purple nonsulfur or green sulfur bacteria were detected. The ratio of zeaxanthin to lutein (above 1:1 in all samples) indicates a dominance of cyanobacteria over green algae in the phytoplankton assemblages of the past. Okenone, which is found exclusively in Chromatiaceae, was the dominating carotenoid in all sediment zones.The oldest sediment layers containing okenone were deposited 11 000 years ago. Between 9000 and 7000 and since 3000 years b.p., Chromatiaceae reached a considerable biomass in the lake. Vertical changes in okenone concentration were not related to changes of paleotemperatures. In contrast, okenone concentrations decreased during periods of volcanic ash input. During most of the lake history, however, mean okenone concentrations were positively correlated with sedimentation rates. This indicates that vertical changes of okenone concentration in the sediment reflect past changes of purple sulfur bacterial biomass in the lake.According to these results, the past limnology of Mahoney Lake resembled that of the present with a sulfide-containing monimolimnion and a well-developed population of okenone-bearing purple sulfur bacteria.     

Dust particle and solar radiation

Influence of the solar radiation (electromagnetic and corpuscular - solar wind) on the motion of the interplanetary dust particle is investigated. The ratio time of inspiralling toward the Sun: time of inspiralling neglecting the change of mass of the particle is presented as a function of initial eccentricities.     

Urban disasters and megacities in a Risk society

Cities like London, New York and Los Angeles possess complex urban environments that, despite their technological sophistication, present their citizens with a multiplicity of risks. This paper presents a discussion of the effects of physical and social trends on the creation of risk and vulnerability to hazard in such cities. The interplay between physical hazards and perceived risks in late modern, or Risk, urban societies is considered, and the impact of this process on adjustment to hazard.     

Problems connected with the tangential metric coefficient in the Schwarzschild metric: A possible solution

Four situations are shown where the Schwarzschild metric cannot be used or is subject to unsurmountable problems. The first is the question of a metric useful for PPN-formalism checking different gravitational theories. The second problem occurs in connection with Mach's principle, when the flatness of the spacetime inside a massive hollow sphere is a generally accepted solution. The metrical discontinuity on the same spherical shell is a third problem. The fourth one is the anisotropy of the mass-energy of a test particle in the gravitational field. Three principles for solution are proposed:

1. The space is not dilated, but rather contracted, in the gravitational field; then the measurement-rods are shorter and measured distances have greater magnitudes.
2. The potential energy is to be related to a potential level where a stationary observer is placed and the general relativistic potential must be used.
3. A new metric must be introduced which is distinct from the Schwarzschild metric, so that the space in the gravitational field is warped isotropically.

Then the problems stated are shown to be easily solvable.     

TheoreticalPKIKP magnitude determination

Summary The estimation of the theoretical magnitude for deep foci based on the vertica component of medium-period PKIKP waves, Earth model PREM and source spectra is presented. The given graphs are valid for period T ranging from 1·6 s to 10 s, source depth of 25 km to 600 km and distance range of 16 500 km to 19 800 km. A simplified method of representing calibration curves is used.     

Investigation of the instability of graveyard orbits due to the earth's gravitational perturbations

Summary The Banach theorem is applied to the Lagrange planetary equation for the semimajor axis of a geostationary satellite orbit to estimate the stability of near-geostationary satellite orbits. To achieve a graveyard (disposal) orbit, which will not interfere (=cross) the initial geostationary orbit, the geostationary semi-major axis a_g have to be increased at least by 50 km. Numerical results for a variety of graveyard orbits show that the increase of a_g by about 100 km will yield sufficiently stable orbits (accounting for the Earth's gravitational perturbations only) during the next 150 years.Dedicated to the 75th Birthday of Professor Academician Tibor Kolbenheyer