A note on two-point paraxial travel times

Recently, several expressions for the two-point paraxial travel time in laterally varying, isotropic or anisotropic layered media were derived. The two-point paraxial travel time gives the travel time from point S′ to point R′, both these points being situated close to a known reference ray Ω, along which the ray-propagator matrix was calculated by dynamic ray tracing. The reference ray and the position of points S′ and R′ are specified in Cartesian coordinates. Two such expressions for the two-point paraxial travel time play an important role. The first is based on the 4 × 4 ray propagator matrix, computed by dynamic ray tracing along the reference ray in ray-centred coordinates. The second requires the knowledge of the 6 × 6 ray propagator matrix computed by dynamic ray tracing along the reference ray in Cartesian coordinates. Both expressions were derived fully independently, using different methods, and are expressed in quite different forms. In this paper we prove that the two expressions are fully equivalent and can be transformed into each other.     

Permafrost occurrence during the Last Permafrost Maximum in the Western Carpathian Mountains of Slovakia as inferred from cryogenic cave carbonate

Coarse crystalline cryogenic cave carbonate (CCC) forms during the slow freezing of standing water pools and represents indirect proof of freezing temperature in the past. The dating by U‐series of CCC deposits from nine caves in the Western Carpathians Mountains of Slovakia suggests that freezing conditions, and possible permafrost conditions, occurred during the Last Permafrost Maximum (LPM, c. 20–18 ka BP). The CCC deposits occur in caves at elevations of between 800 and 1800 m a.s.l. They point to widespread alpine permafrost, the lower limit of discontinuous/sporadic permafrost being approximately 800 m a.s.l. The thickness of permafrost probably varied between 30 and 180 m. In the Vysoké Tatry Mountains at altitudes of ～1800 m a.s.l., one occurrence of CCC suggests that subzero temperatures may have penetrated to a depth of over 285 m.     

Aspects of the long-term cosmic-ray modulation

To investigate the long-term modulation of galactic cosmic rays at the ground-based detector energies, the monthly values of the neutron monitor (Climax, Mt. Washington, Deep River, and Huancayo) and ionization chamber (Cheltenham/Fredericksburg, Huancayo, and Yakutsk) intensities have been correlated with the sunspot numbers (used as a proxy index for transient solar activity) for each phase of sunspot cycles 18 to 22. Systematic differences are found for results concerning odd and even sunspot cycles. During odd cycles (19 and 21) the onset time of cosmic-ray modulation is delayed when compared with the onset time of the sunspot cycle, while they are more similar during even (18, 20, and 22) cycles. Checking the green corona data, on a half-year basis, we found typical heliolatitudinal differences during ascending phases of consecutive sunspot cycles. This finding suggests a significant role of the latitudinal coronal behaviour in the heliospherical dynamics during a Hale cycle. Such effectiveness concerns not only the transient interplanetary perturbations but also the recurrent ones. In fact, when lag between cosmic-ray data and sunspot numbers is considered, the anticorrelation between both parameters is very high (correlation coefficient |r| > 0.9) for all the phases considered, except for the declining ones of cycles 20 and 21, when high-speed solar wind streams coming from coronal holes affect the cosmic-ray propagation, and theRz parameter is no longer the right proxy index for solar-induced effects in the interplanetary medium.     

Determination of origin of NASA stratospheric particles

Paper presents a reanalysis of four stratospheric particles registered in the Cosmic Dust Catalogs (CDC). Two particles have been classifed in the NASA Johnson Space Centre (JSC) in Houston as natural, terrestrial contaminants and the origin of the other two particles was found questionable, probably cosmic. Present study has confirmed these conclusions; however some new additional features in the chemical analysis have been found which can finally determine the classification of the particles with unclear origin.     

Analysis of the time profile of type III bursts at meter wavelengths

The time profile of two sets of isolated type III bursts, observed in the meter wavelength range at the Trieste Astronomical Observatory, was analyzed using a Fourier transform technique in order to accurately determine the decay constant of the exponential phase and to derive the exciter time profile. The decay constant () was found to be correlated with the exciter duration (D _e ), suggesting that the damping of plasma waves is not of collisional origin and confirming results obtained by previous authors at lower frequencies. In particular, two distributions can be identified in the ( – D _e ) plane and fitted by two nearly parallel lines, which could be the signature of different decay processes. Moreover, the damping constant observed at higher frequencies (327 and 408 MHz) has the same dependence on exciter duration as that at the lower frequency (237 MHz), also in disagreement with the collisional hypothesis.     

Primary compositional range and alteration trends of microlite from the yellowknife pegmatite field,Northwest territories,Canada

Summary Microlite occurs as a rare accessory mineral in beryl-columbite, beryl-columbitephosphate, complex spodumene, albite-spodumene and amblygonite type rare-element granitic pegmatites in the Archean Yellowknife pegmatite field of the Canadian Shield. The chemistry of microlite is variable but consistent with the accepted structural formula A_2–mB₂X₆Y_1–n pH₂O, where generally A = Ca,Na; B = Ta,Nb; X = O; Y = O,OH, F; m = 0 - 2; n = 0 - 1 and p = 0 - l. The chemistry of the Yellowknife microlite is dominated by Ca, Na, Ta, and Nb with minor amounts of U, Pb, Fe, Mn, and Ti. The compositions of microlite are interpreted to reflect primary variability and effects of late-stage alteration.Two principal types of microlite can be distinguished by their primary composition and alteration trends. U-poor microlite originated by the metasomatic replacement of pre-existing manganocolumbite, manganotantalite, and ferrotapiolite; with progressive alteration, its composition evolves from early Ca-rich, Fe,Mn-poor members to late Ca,Na-poor, Fe,Mn-enriched members. In contrast, U-bearing microlite formed from U-enriched, moderately fractionated pegmatitec fluids acting upon ferrocolumbite, manganocolumbite, and manganotantalite; with progressive alteration, its composition evolves from U,Ca,Na-enriched members to U,Ca,Na-poor, Fe,Mn-enriched members.

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Primärer zusammensetzungsbereich und umwandlungstrends der mikrolithe aus dem yellowknife pegmatitfeld, Northwest Territories, Kanada

Zusammenfassung Primärer Zusammensetzungsbereich und Umwandlungstrends der Mikrolithe aus dem Yellowknife Pegmatitfeld, Northwest Territories, Kanada Mikrolith kommt in den Beryll-Columbit-, Beryll-Columbit-Phosphat-, komplexen Spodumeri-, Albit-Spodumen- und Amblygonit-Typen der Seltene-Element-Granitpegmatite im archäischen Yellowknife Pegmatitfeld des Kanadischen Schildes als seltenes akzessorisches Mineral vor. Der Chemismus des Mikroliths variiert, ist aber mit der gebräuchlichen Strukturformel A_2–mB₂X_1–mY_1–n·pH₂O verträglich, mit im allgemeinen A = Ca,Na, B = Ta,Nb, X = O, m=0–2, n =O–1 und p=0–1. Der Chemismus des Yellowknife Mikroliths wird durch Ca, Na, Ta und Nb dominiert, U, Pb, Fe, Mn und Ti treten in kleineren Mengen auf. Die Zusammensetzungen des Mikroliths spiegeln die primäre Variabilität sowie die Auswirkungen späterer Umwand lungen wieder.Zwei Haupttypen des Mikroliths können nach ihrer primären Zusammensetzung und den Umwandlungstrends unterschieden werden. U-armer Mikrolith entstand durch metasomatischen Ersatz von früherem Manganocolumbit-Manganotantalit und Ferrotapiolith, mit fortschreitender Umwandlung entwickelt sich seine Zusammensetzung von frühen Ca-reichen, Fe,Mn-armen Gliedern zu späten Ca,Na-armen, Fe,Mn-angereicherten Gliedern. Im Gegensatz dazu bildete sich U-haltiger Mikrolith aus an U angerereicherten, mäßig fraktionierten pegmatitischen Fluiden, die auf Manganocolumbit-Manganotantalit einwirkten, mit fortschreitender Umwandlung entwickelt sich seine Zusammensetzung von U,Ca,Na-angereicherten Gliedern zu U,Ca,Na-armen, Mn,Feangereicherten Gliedern.

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With 9 Figures     

Radiation patterns of point sources situated close to structural interfaces and to the earth's surface

The seismic wave field is considerably influenced by local structures close to the source and to the receiver. This applies to sources and receivers situated close to localized inhomogeneities, to structural interfaces, to the earth's surface, etc. In this paper we concentrate our attention mainly to the ray-theoretical radiation patterns of point sources situated close to the structural interfaces and to the earth's surface. In numerical modeling of high-frequency seismic wave fields by the ray method, the interaction of the source with the earth's surface has not usually been taken into account.The proposed procedure of the computation of the radiation patterns of point sources situated directly on structural interfaces and on the earth's surface is based on the zero-order approximation of the ray method, assuming that the length of the ray between the source and the receiver is long. The derived equations are extended to point sources located close to structural interface, to the earth's surface and to thin transition layers using the hybrid ray-reflectivity method, seeervený (1989). The thin layer need not be homogeneous; it may include an arbitrary inner layering (transition layers, laminas, etc.) The only requirement is for the layer to be thin. Roughly speaking, we require its thickness to be less than one quarter of the prevailing wavelength. The hybrid ray-reflectivity method describes well even certain non-ray effects (tunneling.S ^* waves, etc.). Explicit analytical expressions for radiation patterns for all above listed point sources are found. These expression have a local character and may be easily implemented into computer codes designed for the routine computation of ray amplitudes and synthetic ray seismograms in 2-D and 3-D, laterally varying isotropic layered and block structures by the ray method.Numerical examples of radiation patterns ofP andS waves of point sources situated close to the earth's surface and to a thin low-velocity surface layer are presented and discussed. The explosive point source (center of dilatation) and the vertical and horizontal single force point sources are considered. It has been ascertained that the radiation patterns of point sources depend drastically on the depth of the source below the surface even if the depths vary within one quarter of the prevailing wavelength.     

The analysis of four cosmic dust particles

A set of four stratospheric particles was reanalysed. These particles registered in the NASA Cosmic Dust Catalogs (CDCs) were classified in the Houston Johnson Space Center (JSC) as the particles of cosmic origin (C). Present energy-dispersive X-ray (EDX) spectra confirmed previous classification and revealed additional features in the chemical composition of the cosmic dust particles.The particles are extremely fine-grained aggregates with bulk chondritic composition. Somewhat higher content of oxygen may indicate a presence of hydroxide containing minerals in their phase composition.     

Le développement de la géodésie et cartographie tchécoslovaque de 1945 a 1940

Sans résumé En collaboration avec les membres de la rédaction: prof. Ing. Ján Krajčí, Dr. Ing. Karel Kučera et Dr. Ing. Jan Kašpar. Adresse: Národní tř. 3, Praha 1.