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41.
The geological record of the Western Andean Escarpment (WARP) reveals episodes of uplift, erosion, volcanism and sedimentation. The lithological sequence at 18°S comprises a thick pile of Azapa Conglomerates (25–19 Ma), an overlying series of widespread rhyodacitic Oxaya Ignimbrites (up to 900 m thick, ca. 19 Ma), which are in turn covered by a series of mafic andesite shield volcanoes. Between 19 and 12 Ma, the surface of the Oxaya Ignimbrites evolved into a large monocline on the western slope of the Andes. A giant antithetically rotated block (Oxaya Block, 80 km×20 km) formed on this slope at about 10–12 Ma and resulted in an easterly dip and a reversed drainage on the block's surface. Morphology, topography and stratigraphic observations argue for a gravitational cause of this rotation. A “secondary” gravitational collapse (50 km3), extending 25 km to the west occurred on the steep western front of the Oxaya Block. Alluvial and fluvial sediments (11–2.7 Ma) accumulated in a half graben to the east of the tilted block and were later thrust over by the rocks of the escarpment wall, indicating further shortening between 8 and 6 Ma. Flatlying Upper Miocene sediments (<5.5 Ma) and the 2.7 Ma Lauca–Peréz Ignimbrite have not been significantly shortened since 6 Ma, suggesting that recent uplift is at least partly caused by regional tilting of the Western Andean slope. 相似文献
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Hartmut W. Hoeness Rudolf Mueller Erich W. Rodeck Friedrich B. Siebers 《Astrophysics and Space Science》1989,160(1-2):193-197
For about 20 years SCHOTT has been supplying the glass ceramic ZERODUR, a material with very low thermal expansion. Besides many other applications, ZERODUR is excellently suited for the manufacture of mirror substrates for telescopes. About 80% of all telescopes in the western world with mirror diameters >1.8 m have been equipped with ZERODUR during the last 10 years. The development of modern astronomical telescopes is aimed at larger primary mirrors and lighter secondary mirrors.New techniques have been developed by SCHOTT for manufacture of thin monolithic mirror blanks of more than 8 m in diameter. The development of thin meniscus shaped shells using the spin-casting technique was successfully completed last year. During a test production several mirror substrates up to 4.1 m in diameter and down to 57 mm in thickness could be produced. The know-how has been acquired for the fabrication of mirror substrates of more than 8 m in diameter by the spin-casting technique.SCHOTT has also performed considerable developmental work in the field of lightweighted ZERODUR mirror substrates which can be generated using different techniques: forming of the lightweighted structure during casting, fusion of individual components to a total structure and lightweighting of a massive block by various mechanical machining methods.Paper presented at the Symposium on the JNLT and Related Engineering Developments, Tokyo, November 29–December 2, 1988.Registered trademark of SCHOTT Glaswerke, Mainz. 相似文献
44.
The impact of thermally induced microfractures on the stress‐sensitive elastic wave properties of aeolian Rotliegend sandstone samples is analysed. It is found that to identify the effects of the microfracture contribution accurately, a correction must first be made to account for water loss (representing a mass loss of 4–6%) from the pore throats and clays due to the heating process, despite care being taken to ensure that the thermally fractured samples re‐adsorb room moisture. Both the original and thermally fractured rocks are stress‐sensitive at the ultrasonic wave frequencies of the laboratory. However, a distinct shift in the estimated distribution of internal rock compliance indicates that the population of thermal microfractures differs in nature from that caused solely by core‐plug extraction damage. In particular, the ratio of normal to tangential compliance is observed to be higher for the thermally generated microfractures than for the broken grain‐grain contacts created by extraction unloading. This can be explained by the intragranular thermal‐fracture surfaces being smoother when compared to the intergranular boundaries. Mechanical hysteresis is observed between the up‐ and downgoing test cycles for both the original and, to a greater extent, the thermally fractured rock. This indicates that there is compaction‐induced movement of the fractures in the samples during application of stress in the laboratory. 相似文献
45.
The photospheric barium spectrum: Solar abundance and collision broadening of Baii lines by hydrogen
A study of the solar Ba ii spectrum leads to a solar abundance of barium of log
ba = = 2.11±0.12, on the scale log
h = 12. The observed asymmetry of the resonance line 4554 is consistent with an isotopic abundance ratio equal to the terrestrial one. The meteoritic Ba/Si abundance ratio found in carbonaceous chondrites appears to exceed the solar ratio by 0.1 to 0.2 dex (Section 5).The broadening by collisions with hydrogen atoms is determined from the solar spectrum (Section 4). Damping half-widths,
h, of the three stronger Ba ii lines turn out to be larger by a factor of about 3.0 than predicted from pure van der Waals interaction of dipoles.
Departures from LTE appear to be present in the cores of the resonance lines and of the lines arising from the metastable 5D levels (Section 6). The equivalent widths, however, remain practically unaffected.Equivalent widths of neutral barium lines are predicted and some new identifications of photospheric Ba i lines are suggested (Section 7). 相似文献
46.
Using a single drop experiment, the uptake of NO3 radicals on aqueous solutions of the dye Alizarin Red S and NaCl was measured at 293 K. Uptake coefficients in the range
(1.7–3.1) ⋅ 10− 3 were measured on Alizarin Red S solutions. The uptake coefficients measured on NaCl solutions were in the range of (1.1–2.0)
⋅ 10−3 depending on the salt concentration. Both experiments lead to a consistent result for the mass accommodation coefficient
of αNO3 = (4.2− 1.7+2.2)⋅ 10−3.
The product H(Dl kCl−II)0.5 for the NO3 radical was determined to be (1.9 ± 0.2) M atm− 1 cm s−0.5 M−0.5 s−0.5 by fitting the uptake data for the NaCl solutions to the so-called resistance model.
The yield of the chemical NO3 radical source was characterized using UV-VIS and FT-IR spectroscopy. The amount of gas-phase NO3 radicals measured at elevated humidities was less than expected. Instead, a rise of the gas-phase HNO3 concentration was found indicating a conversion of gas-phase NO3 radicals to gas-phase HNO3 on the moist reactor walls. 相似文献
47.
Hartmut Grassl 《Surveys in Geophysics》2011,32(4-5):319-328
Anthropogenic climate change has emerged as one of the major challenges for mankind in the centuries to come. The strongly modified composition of the atmosphere, due to emissions of greenhouse gases and aerosol particles, leads to an enhanced greenhouse effect and also intensified backscattering of solar radiation by aerosol particles. The resulting global mean warming will have a major impact on the entire cryosphere, with global consequences via mean sea level rise and redistributed precipitation. This introductory presentation will summarize the emergence of the topic, its already observed consequences for the cryosphere, and it will also discuss issues in climate policy making when dealing with the climate change challenge. 相似文献
48.
Analysis of lightning-induced forest fires in Austria 总被引:1,自引:0,他引:1
Mortimer M. Müller Harald Vacik Gerhard Diendorfer Alexander Arpaci Herbert Formayer Hartmut Gossow 《Theoretical and Applied Climatology》2013,111(1-2):183-193
Besides human-caused fires, lightning is the major reason for forest fire ignition in Austria. In order to analyse the causes of ignition and to characterise lightning-induced forest fires, fire records were compared with the real appearance of lightning events by using the Austrian Lightning Detection and Information System for the period from 1993 to 2010. A probability was estimated for each forest fire being caused by lightning by using a decision tree and decision matrices based on flash characteristics (e.g. amplitude, time, location). It could be shown that 15 % of documented forest fires were lightning-caused. Nearly all lightning-caused fires were found during the summer months, whereas almost 40 % of all fires occurring from June to August were naturally caused. Most lightning-caused fires took place in the south and east of Austria. Lightning fires were more frequent at higher altitudes and primarily affected conifer forests. The median burned area was lower than that for anthropogenic forest fires. 相似文献
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