Age of the Laschamp paleomagnetic excursion revisited

The reverse paleomagnetism of the lava flows of Laschamp and Olby, already discovered by Bonhommet and Babkine, is confirmed. The ages of these flows, measured by¹⁴C, thermoluminescence and K-Ar dating are respectively36,000 ± 4000 and42,000 ± 5000years. VGP's comparison of the “Laschamp event” with those of the 30,000-year Lake Mungo excursion does not show evidence of coincidence between these two events.     

Permanganate oxidation products of algal humic-like substances

Algal humic-like substances were oxidized with KMnO₄. The oxidation products were analyzed by GC-MS. Normal and branched fatty acids, dicarboxylic and benzene carboxylic acids were identified. Aliphatic acids were by far the most prominent compounds. Similarities between humic and fulvic acids of both Fucus and Laminaria algae were apparent. Fucus humic acids, however, showed a more aromatic structure than their Laminaria counterpart. The contribution of algae to marine sedimentary humus is discussed.     

A comment on the effect of discretization on dispersion

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Numerical properties of low-frequency expansions for the reflection and transmission coefficients from transition layers

Summary The numerical properties of the low-frequency expansions for the reflection and transmission coefficients of SH-waves from transition layers, derived in [1], are studied. It is shown that the expansions are suitable for computations only when the thickness d of the transition layer is small in comparison with the wavelength of the incident wave (d0.5). For thicker transition layers, certain modifications of the method are suggested.     

Relation between the monthly sums of sunshine and global radiation

Summary The statistical treatment of the dependence of monthly sums of global radiation on the monthly sums of sunshine at the stations of Hradec Králové, Bratislava — Koliba and Hurbanovo is presented. The parameters of linear and quadratic regression are derived for the said stations and for the individual months of the year. Drawing on the statistical analysis of the initial data sets, the accuracy and reliability of the mentioned regression relations are critically evaluated.     

Macroseismic observations of earthquake in Yugoslavia (April 15, 1979, 06h21m gmt), on the territory of Czechoslovakia

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Subgrain boundaries in quartz theoretical analysis and microscopic observations

At moderate temperature (T≈1/3 T _Melt) recovery processes become very active in wet quartz and many subgrain boundaries (sgb's) are formed which still contain interesting information on the deformation mechanisms. In particular, the geometrical characteristics of a sgb (normal, rotation axis) depend upon the glide systems which have been activated. Possible sgb's in quartz are studied from a theoretical point of view with the help of the Frank formula. The predictions are compared with observations by optical microscopy and by transmission electron microscopy (TEM) on naturally deformed quartz samples. Most of the predicted sgb's are effectively observed and there is an excellent agreement between theory and observation. This allows a rapid characterization of sgb's in tem to be performed by standard stereographic methods: only the directions of the dislocations and the plane of the sgb are determined; they are compared to a table deduced from geometrical considerations and the glide systems which have been activated during the deformation (at least the last stage of deformation) can be deduced. This method is very important for the case of quartz because the rapid irradiation of this material under the electron beam renders very difficult the characterization of the Burgers vectors of free dislocations. A similar method can be developed for observations in optical microscopy when the crystallographic orientation of the studied thin sections can be determined.