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排序方式: 共有162条查询结果,搜索用时 15 毫秒
51.
Addi BISCHOFF Miha JERSEK Thomas GRAU Breda MIRTIC Ulrich OTT Jan KUČERA Marian HORSTMANN Matthias LAUBENSTEIN Siegfried HERRMANN Zdeněk ŘANDA Marc WEBER Gerd HEUSSER 《Meteoritics & planetary science》2011,46(6):793-804
Abstract– On April 9, 2009, at 3:00 CEST, a very bright fireball appeared over Carinthia and the Karavanke Mountains. The meteoroid entered the atmosphere at a very steep angle and disintegrated into a large number of objects. Two main objects were seen as separate fireballs up to an altitude of approximately 5 km, and witnesses reported loud explosions. Three stones were found with a total weight of approximately 3.611 kg. The measured activity of short‐lived cosmogenic radionuclides clearly indicates that two specimens result from a very recent meteorite fall. All cosmogenic radionuclide concentrations suggest a rather small preatmospheric radius of <20 cm; a nominal cosmic‐ray exposure age based on 21Ne is approximately 4 Ma, but the noble gas and radionuclide results in combination indicate a complex irradiation. Jesenice is a highly recrystallized rock with only a few relic chondrules visible in hand specimen and thin section. The texture, the large grain size of plagioclase, and the homogeneous compositions of olivines and pyroxenes clearly indicate that Jesenice is a L6 chondrite. The bulk composition of Jesenice is very close to the published average element concentration for L ordinary chondrites. The chondrite is weakly shocked (S3) as indicated by the undulatory extinction in olivine and plagioclase and the presence of planar fractures in olivine. Being weakly shocked and with gas retention ages of >1.7 Ga (4He) and approximately 4.3 Ga (40Ar), Jesenice seems not to have been strongly affected by the catastrophic disruption of the L‐chondrite parent body approximately 500 Ma ago. 相似文献
52.
Marian Marschalko Işık Yilmaz Veronika Křístková Matěj Fuka Martin Bednarik Karel Kubečka 《Engineering Geology》2012
This study deals with the determination of the actual limit angles in the long-term formed subsidence basin in the Czech part of the Upper Silesian Basin (the remaining part lays in Poland). Here there was the most extensive underground exploitation of black coal in the north-east of the Czech Republic. A limit angle is absolutely decisive in the determination of deep mining influences in relation to the current and future utilisation of this territory. The two CSM and Paskov mine localities on the edge of the subsidence basin were selected for this study, since they could not have been affected by mining in neighbouring mines. On the grounds of the long-term levelling monitoring of points on the surface which started prior to mining, the horizontal distance between the mined out area and the undisturbed ground surface was identified. The impact of limit angle on the surface was calculated by means of the horizontal distance and the established mining depth. Such identified actual limit angles reached the values of 36° at the CSM Mine and 25° for the Paskov Mine. The calculated values are significantly lower when compared with the currently applied empirical values of 57° for the CSM Mine and 56° for the Paskov Mine. This means that the extent of the undermining effects is unambiguously wider by 611 m at the CSM Mine and by 883 m at the Paskov Mine. This study thus establishes the existence of a significantly vaster area influenced by coal deep mining than previously expected. The identified facts lead to the conclusion that regular revisions and follow-up updates of the empirically determined parameters are recommended. 相似文献
53.
Marian?B.?HolnessEmail authorView authors OrcID profile Robert?Farr Jerome?A.?Neufeld 《Contributions to Mineralogy and Petrology》2017,172(1):7
The 168 m-thick Shiant Isles Main Sill is a composite body, dominated by an early, 24 m-thick, picrite sill formed by the intrusion of a highly olivine-phyric magma, and a later 135 m-thick intrusion of olivine-phyric magma that split the earlier picrite into a 22 m-thick lower part and a 2 m-thick upper part, forming the picrodolerite/crinanite unit (PCU). The high crystal load in the early picrite prevented effective settling of the olivine crystals, which retain their initial stratigraphic distribution. In contrast, the position of the most evolved rocks of the PCU at a level ~80% of its total height point to significant accumulation of crystals on the floor, as evident by the high olivine mode at the base of the PCU. Crystal accumulation on the PCU floor occurred in two stages. During the first, most of the crystal load settled to the floor to form a modally and size-sorted accumulation dominated by olivine, leaving only the very smallest olivine grains still in suspension. The second stage is recorded by the coarsening-upwards of individual olivine grains in the picrodolerite, and their amalgamation into clusters which become both larger and better sintered with increasing stratigraphic height. Large clusters of olivine are present at the roof, forming a foreshortened mirror image of the coarsening-upwards component of the floor accumulation. The coarsening-upwards sequence records the growth of olivine crystals while in suspension in a convecting magma, and their aggregation into clusters, followed by settling over a prolonged period (with limited trapping at the roof). As olivine was progressively lost from the convecting magma, crystal accumulation on the (contemporaneous) floor of the PCU was increasingly dominated by plagioclase, most likely forming clusters and aggregates with augite and olivine, both of which form large poikilitic grains in the crinanite. While the PCU is unusual in being underlain by an earlier, still hot, intrusion that would have enhanced any driving force for convection, we conclude from comparison with microstructures in other sills that convection is likely in tabular bodies >100 m thickness. 相似文献
54.
55.
Elisabetta Boaretto Charlotte Bryant Israel Carmi Gordon Cook Steinar Gulliksen Doug Harkness Jan Heinemeier John McClure Edward McGee Philip Naysmith Goran Possnert Marian Scott Hans van der Plicht Mark van Strydonck 《第四纪科学杂志》2002,17(7):633-637
Interlaboratory comparisons have been widely used in applied radiocarbon science. These are an important part of ongoing quality assurance (QA) programmes, which are vital to the appropriate interpretation of the evidence provided by the 14C record in Quaternary applications (including climate change and environmental reconstruction). International comparisons of laboratory performance are an essential component of the quality assurance process in radiocarbon dating. If the user community is to have confidence in radiocarbon results, it needs to be assured that laboratories world wide are producing measurements that are reliable and in accordance with ‘good practice’. The findings from the most recent (completed in 2001) and extensive (more than 90 participating laboratories) radiocarbon intercomparison (FIRI) are reported here. This study was designed (i) to assess comparability, or otherwise, of the results from different laboratories and (ii) to quantify the extent and possible causes of any interlaboratory variation. The results demonstrate that there are no significant differences amongst the main measurement techniques (gas proportional counting, liquid scintillation counting and accelerator mass spectrometry (AMS)) but there is evidence of small laboratory offsets relative to known age samples for some laboratories. There is also evidence in some cases of underestimation of measurement precision. Approximately 10% of all results were classified as extreme (outliers) and these results were generated by 14% of the laboratories. Overall, the evidence supports the fact that radiocarbon laboratories are generally accurate and precise but that, notwithstanding internal QA procedures, some problems still occur, which can best be detected by participation in independent intercomparisons such as FIRI, where the results allow individual laboratories to assess their performance and to take remedial measures where necessary. The results from FIRI are significant in that they show a broad measure of agreement between measurements made in different laboratories on a wide range of materials and they also demonstrate no statistically significant difference between measurements made by radiometric or AMS techniques. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
56.
We performed a statistical analysis of the dm-spikes that were present for an exceptionally long period (more than 10 min) during the 15 June 1991 flare. We realized that the polarization degree, the duration and the mutual delay of the R- and L-components were nearly the same for both CW and ACW cases. CW (ACW) means the clockwise (anti-clockwise) sense of the loop in the R–L versus L+R plots, when the data of a single spike are considered according to the time sequence. The presence of such a loop is determined by the delay of the weaker (stronger) polarimetric component in respect to the other one. The increase of the polarization percentage started first at 610, then at 408 and afterwards at 327 MHz. It was found that the duration of spikes was almost completely independent from the polarization degree. The mean duration of spikes at different frequencies corresponds to that computed using the formula of Güdel and Benz. Like the mean duration, also the mean delay decreased with increasing frequency. The CW/ACW ratio varied simultaneously for the frequencies we recorded during an interval of about three minutes. Spikes were considered as the radio manifestation of superthermal electrons accelerated in the MHD cascading waves. The evolution of spikes and their parameters were qualitatively interpreted within the flare reconnection model with turbulent plasma outflows. 相似文献
57.
We present observations of optical spectra of a flare in which blue line asymmetry was seen for more than 4 min close to the flare onset. The maximum blue asymmetry coincided with the maximum of a hard X-ray and microwave burst. We discuss possible interpretations of the blue asymmetry and conclude that the most plausible one is electron-beam heating with return current. Although this process predicts downflows in the lower transition region and upper chromosphere, its ultimate effect on the line profiles can be blue asymmetry: the upper layers moving away from us absorb the radiation of the red peak thus lowering its intensity in comparison to the blue one. 相似文献
58.
Jan Wiszniowski Marian Hościłowicz Andrzej Skrzyński Jerzy Suchcicki Krzysztof P. Teisseyre 《Acta Geophysica》2008,56(2):391-407
A method of correcting the seismometers’ responses discrepancy for differential measurements of strains and rotations in the
seismic far field is proposed. The method concerns differential calibration of the whole seismometers’ array by electric current.
A model of corrective filtering of the obtained differential signals in the Z domain is given. Two methods of the filter parameters’
estimation are introduced; they are based on the seismometers response to the calibration.
A practical test of the methods — an analysis of a recorded seismic event — is added. Significant reduction of differences
between simultaneous seismic recordings was obtained, which is interpreted as cleaning of differential signal from spurious
elements. 相似文献
59.
Vratislav Hurai Marian Janák Rainer Thomas 《Contributions to Mineralogy and Petrology》2010,160(2):203-218
Fluid inclusions in garnet combined with element X-ray mapping, phase equilibrium modelling and conventional thermobarometry
have been used to constrain the metamorphic evolution of metapelitic gneiss from the HP/UHP metamorphic terrane of Pohorje
Mountains in the Eastern Alps, Slovenia. Retrograde P–T trajectory from ~2.75 GPa and 780°C is constrained by the composition of matrix phengite (6.66 apfu Si) coexisting with garnet
cores, kyanite and quartz. The intersection of the X
Prp = 0.25 isopleth for the garnet with the upper stability boundary for K-feldspar in the matrix indicates near-isothermal decompression
to ~0.9 GPa at 720°C. Temperatures over 650°C during this stage are corroborated by the high degree of ordering of graphite
inclusions associated with Zn, Mg-rich staurolite and phlogopite in the Mg-rich (X
Prp = 0.22–0.25) garnet cores. Majority of garnet porphyroblasts are depleted in Mg (down to X
Prp = 0.09) and enriched in Mn (up to X
Sps = 0.12) along cracks and at their margins. The associated retrograde mineral assemblage comprises Zn, Mg-poor staurolite,
muscovite, biotite–siderophyllite, sillimanite and quartz. The onset of the retrogression and the compositional modification
of the garnet porphyroblasts were accompanied by the addition of fluid-deposited graphite around older graphite inclusions,
probably due to removal of water from a graphite-buffered COH fluid by dissolution in partial silicic melt. Instantaneous
expulsion of water near the melt solidus (640°C, max. 0.45 GPa) caused dissolution of the graphite at redox conditions corresponding
to 0.25–1.25 logfO2 units below the QFM buffer, giving rise to a H2O–CO2–CH4 fluid trapped in primary inclusions in Mn-rich, Mg-poor, almandine garnet that reprecipitated within the retrogressed domains.
The absence of re-equilibration textures and consistent densities of the fluid inclusions reflect a near-isochoric cooling
postdating the near-isothermal decompression. Bulk water content in the metapelite attained 2 wt% during this stage. The low-degree
partial melting and extensive hydration due to the release of the internally derived, low-pressure aqueous fluids led to the
reset of peak-pressure mineral assemblage. 相似文献
60.
Marian Družkowski 《Environmental Geology》2000,40(1-2):90-98
Research into the patterns of natural underground water effluents has been conducted in a small catchment basin (Wierzbanówka)
that is representative of the Carpathian foothills. The aim of this study was to understand the long-term dynamics of the
effluents and their responses to natural and artificial factors in order to estimate groundwater resources. High variability
of the effluent patterns in the Carpathian foothills is a result of precipitation fluctuations, low ground retention capacity,
a low rate of absorption in the flysch rock formation areas, and of the Quaternary covers. In addition, the dominance of agricultural
land use, low forest coverage, and poor hydrological management are the main causes of this variability. Any local increase
in underground water resources would only be possible if forests were planted on some of the agricultural land and changes
were made to water management.
Received: 16 August 1999 · Accepted: 12 January 2000 相似文献