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

A. Abrami  M. Messerotti  P. Zlobec  M. Karlický 《Solar physics》1990,130(1-2):131-138

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.  相似文献   

Tunneling of seismic body waves through thin high-velocity layers in complex structures     

Vlastislav Červený  Paulo R. A. Aranha 《Studia Geophysica et Geodaetica》1992,36(2):115-138

Summary The hybrid ray-reflectivity method is applied to the problem of the transmission of the reflected wave field through a thin high-velocity layer (or through a thin stack of high velocity layers), situated in the overburden of the reflector. In the hybrid ray-reflectivity method, the standard ray method is applied in the smooth parts of the model, and the reflectivity method is used locally at the thin high-velocity layer. With the exception of small epicentral distances, the standard ray method itself fails in such computations. The reason is that a considerable part of the energy for overcritical angles of incidence may be tunneled through the thin high-velocity layer along complex ray-paths, corresponding to inhomogeneous waves. The reflectivity method, applied locally at the thin high-velocity layer, automatically includes all inhomogeneous wave contributions. Thus, the hybrid ray-reflectivity method removes fully the limitations of the standard ray method, but still retains its main advantages, such as its applicability to 2-D and 3-D complex layered structures, flexibility, and low-cost computations. In the numerical examples, the hybrid ray-reflectivity synthetic seismograms are compared with standard ray synthetic seismograms and with full reflectivity computations. The numerical examples show that the hybrid ray-reflectivity method describes the tunneling of seismic energy through a thin high-velocity layer with sufficient accuracy.  相似文献   

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

M. A. Wise  P. Černý 《Mineralogy and Petrology》1990,43(2):83-98

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  相似文献   

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

Pert Jílek  Vlastislav Červený 《Pure and Applied Geophysics》1996,148(1-2):175-225

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.  相似文献   

The analysis of four cosmic dust particles     

I. Kapišinský  V. Figusch  A. Hajduk  J. Ivan  K. Iždinský 《Earth, Moon, and Planets》1995,68(1-3):347-360

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.  相似文献   

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

Josef Ryšavý 《Studia Geophysica et Geodaetica》1960,4(2):119-129

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.  相似文献   

A note on the problem of choosing a model of the Universe,III     

Vladimír Skalský 《Astrophysics and Space Science》1989,162(1):171-173

From the analysis of relativistic and quantum-mechanical processes at the creation of the expansive evolution phase of the Universe it follows that the Universe can expand only by the limit velocity of signal propagationc.  相似文献   

Cosmogenic radionuclides and mineralogical properties of the Chelyabinsk (LL5) meteorite: What do we learn about the meteoroid?          下载免费PDF全文

Pavel P. Povinec  Matthias Laubenstein  A. J. Timothy Jull  Ludovic Ferrière  Franz Brandstätter  Ivan Sýkora  Jozef Masarik  Juraj Beňo  Andrej Kováčik  Dan Topa  Christian Koeberl 《Meteoritics & planetary science》2015,50(2):273-286

On February 15, 2013, after the observation of a brilliant fireball and a spectacular airburst over the southern Ural region (Russia), thousands of stones fell and were rapidly recovered, bringing some extremely fresh material for scientific investigations. We undertook a multidisciplinary study of a dozen stones of the Chelyabinsk meteorite, including petrographic and microprobe investigations to unravel intrinsic characteristics of this meteorite. We also study the short and long‐lived cosmogenic radionuclides to characterize the initial meteoroid size and exposure age. Petrographic observations, as well as the mineral compositions obtained by electron microprobe analyses, allow us to confirm the classification of the Chelyabinsk meteorite as an LL5 chondrite. The fragments studied, a few of which are impact melt rocks, contain abundant shock melt veins and melt pockets. It is likely that the catastrophic explosion and fragmentation of the Chelyabinsk meteoroid into thousands of stones was in part determined by the initial state of the meteoroid. The radionuclide results obtained show a wide range of concentrations of ¹⁴C, ²²Na, ²⁶Al, ⁵⁴Mn, ⁵⁷Co, ⁵⁸Co, and ⁶⁰Co, which indicate that the pre‐atmospheric object had a radius >5 m, consistent with other size estimates based on the magnitude of the airburst caused by the atmospheric entry and breakup of the Chelyabinsk meteoroid. Considering the observed ²⁶Al activities of the investigated samples, Monte Carlo simulations, and taking into account the ²⁶Al half‐life (0.717 Myr), the cosmic‐ray exposure age of the Chelyabinsk meteorite is estimated to be 1.2 ± 0.2 Myr. In contrast to the other radionuclides, ¹⁴C showed a very large range only consistent with most samples having been exposed to anthropogenic sources of ¹⁴C, which we associate with radioactive contamination of the Chelyabinsk region by past nuclear accidents and waste disposal, which has also been confirmed by elevated levels of anthropogenic ¹³⁷Cs and primordial ⁴⁰K in some of the Chelyabinsk fragments.  相似文献   

The model of a flat (Euclidean) expansive homogeneous and isotropic relativistic Universe in the light of the Wilkinson Microwave Anisotropy Probe (WMAP) observations     

Vladimír Skalský 《Astrophysics and Space Science》2009,324(1):1-4

The Wilkinson Microwave Anisotropy Probe (WMAP) confirmed the model of a flat (Euclidean) expansive homogeneous and isotropic relativistic universe with the total zero mass (energy), which describes the properties of our observed expansive homogeneous and isotropic relativistic Universe in the first (linear, Newtonian or classical-mechanical) approximation.  相似文献   

The computation of the elastic constants of an anisotropic medium from the velocities of body waves     

Karel Klíma  Reviewer V. Červený 《Studia Geophysica et Geodaetica》1973,17(2):115-122

¶rt;m n¶rt;u nu nm n m . m¶rt; n¶rt;am nuuu am uma au muna (6) u (10). amua aumnu m m nn unam u u, m nmu ama mm (u. 2). uu nu nm ¶rt;u am mu n¶rt; uua 15mu anau u mu u nn uua mu anau. u unauu m nn ¶rt;u am mu n¶rt; uua ¶rt; 21 anau.

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Dedicated to 90th Birthday of Professor Frantiek Fiala  相似文献