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排序方式: 共有253条查询结果,搜索用时 15 毫秒
11.
12.
Reinhard Kanne 《洁净——土壤、空气、水》1995,23(3):140-140
13.
Friedemann Freund Heinz Wengeler Reinhard Martens 《Geochimica et cosmochimica acta》1982,46(10):1821-1829
Water dissolved in a nominally anhydrous oxide like MgO forms not only OH? ions, as is usually assumed, but also molecular H2 and peroxy anions O22?. The specific lattice site where this reaction occurs has been identified for the model-type MgO structure: it is the fully OH? compensated cation vacancy. In partially deuterated synthetic MgO, molecular D2 forms preferentially to H2, by a factor of the order of 4. Three methods have been used to study this very large D/H fractionation experimentally: mass spectrometry, electron spin resonance and infrared spectroscopy. All give consistent results and confirm that internal D/H fractionation occurs and is a function of the temperature. Theoretically the D/H fractionation is explained by the lower zeropoint energy of D2 with respect to H2, amplified by secondary processes through which the molecular hydrogen species become mobilized and eventually lost via diffusion. The possible consequences of such internal D/H fractionation processes are indicated for the interpretation of water and hydrogen release patterns, with varying D/H ratios, from terrestrial and extraterrestrial samples. 相似文献
14.
Recent climate change: Rethinking drought in the context of Forest Fire Research in Ticino, South of Switzerland 总被引:3,自引:1,他引:3
Summary We analyse trends over the past 32 years in drought variables in the context of forest fire research and climate change in Ticino, Southern Switzerland. January to April and in particular the month of March have become drier. This is the time of the year when forest fires are most frequent. Our results show an increasing trend in all climatic variables favourable to drought and forest fires, including the length of episodes without precipitation, sunshine duration and temperature, and a decrease in relative humidity. The only exception is the number of “foehn” days, which have not significantly increased. 相似文献
15.
Philipp Strauss Michael Wagreich Kurt Decker Reinhard F. Sachsenhofer 《International Journal of Earth Sciences》2001,90(3):549-559
The Miocene intramontane Fohnsdorf-Seckau Basin is situated at the junction of the sinistral Mur-Mürz-fault system and the dextral Pöls-Lavanttal fault system. The basin comprises a 2,400-m-thick coal-bearing fluviodeltaic-lacustrine succession (Lower to Middle Miocene, Upper Karpatian?/Lower Badenian) which is overlain by a 1,000-m-thick alluvio-deltaic conglomeratic succession (Apfelberg Formation, ?Middle/Upper Badenian) in the south. A three-stage model for the basin evolution has been reconstructed from structural analysis and basin fill geometries. During a first pull-apart phase, subsidence occurred along ENE-trending, sinistral strike-slip faults of the Mur-Mürz fault system and NE-SW to N-S-trending normal faults, forming a composite pull-apart basin between overstepping en-echelon strike-slip faults. The Seckau and Fohnsdorf sub-basins are considered as two adjacent pull-aparts which merged into one basin. During the second phase, N-S to NNW-SSE extension and normal faulting along the southern basin margin fault formed a half-graben, filled by wedge-shaped alluvial strata (Apfelberg Formation). During the third phase, after the end of basin sedimentation, the dextral Pöls-Lavanttal fault system reshaped the western basin margin into a positive flower structure. 相似文献
16.
Reinhard F. Sachsenhofer 《International Journal of Earth Sciences》2001,90(3):579-592
The heat flow evolution of a continental collisional zone is exemplified by the Eastern Alps. Heat flow maps for the syn-collision (Oligocene), syn-extrusion (Early/Middle Miocene), and post-extrusion (Late Miocene, Recent) stages are presented, and are discussed in relation to the orogenic evolution. Continental collision during Paleogene time was characterized by extremely low heat flow (<40 mW/m2) along the orogenetic front, and very high heat flow (>150 mW/m2) a few hundred kilometers south of it. The former was a result of crustal thickening and of thermal blanketing due to rapid sedimentation and nappe stacking. The latter was caused by slab break-off and magmatic activity. The Early/Middle Miocene syn-extrusion stage was characterized by rapid exhumation of metamorphic core complexes (Tauern and Rechnitz Windows), and by magmatic activity (Styrian Basin). Both mechanisms caused extremely high heat flow (>200 mW/m2). In contrast, the orogenetic front remained cold. Thereafter, magmatic activity ended and uplift rates decreased. Thus, Late Miocene heat flow is characterized by low to moderately high values. Heat flow values >75 mW/m2 were restricted to the transition zone of the Pannonian Basin characterized by thinned crust, and to the Tauern Window area. Recent temperature data indicate a subtle post-Miocene increase in heat flow. 相似文献
17.
Martin Gast Wolfgang Schaaf Joerg Scherzer Rudolf Wilden Bernd U. Schneider Reinhard F. Hüttl 《Journal of Geochemical Exploration》2001,73(2):196
To analyze the development of pine ecosystems on lignite and pyrite containing mine soils, four pine stands with ages of 3–35 years were investigated in a chronosequence approach. Bulk precipitation, throughfall and soil solution in depths of 20, 40, 70 and 100 cm were studied over a three-year period to determine element fluxes in these forest ecosystems on extreme acidic and saline soils.Element budgets are controlled by the processes induced by pyrite oxidation such as intensive weathering of primary minerals, precipitation and leaching of secondary phases.Despite low water fluxes, element outputs can reach extraordinary high values due to very high concentrations in the soil solution. Although element outputs decrease drastically with stand age, respectively, site age, they exceed those of comparable pine stands on non-mine sites. Nitrogen release from the lignite fraction represents a special characteristic of the examined substrates. Nitrogen losses beneath the rooted zone can be 34 kg N ha−1 yr−1 in 100 cm depth. Element input and output in the examined ecosystems are far from balance. Closed cycling of nutrients seems to be recognizable in the case of potassium. 相似文献
18.
19.
Detailed facies analysis of hyaloclastites and associated lavas from eight table mountains and similar "hyaloclastite volcanoes"
in the Icelandic rift zone contradict a rapid and continuous, "monogenetic", entirely subglacial evolution of most volcanoes
studied. The majority of the exposed hyaloclastite deposits formed in large, stable lakes as indicated by widespread, up to
300-m-thick, continuous sections of deep water, shallow water and emergent facies. Salient features include extensively layered
or bedded successions comprising mainly debris flow deposits, turbidites, base surge and fallout deposits consisting of texturally
and compositionally variable, slightly altered hyaloclastites, as well as sheet and pillow lavas. In contrast, chaotic assemblages
of coarser-grained, more poorly sorted and more strongly palagonitized hyaloclastite tuffs and breccias, as well as scoria
and lava are interpreted to have formed under sub- or englacial conditions in small, chimney-like ice cavities or ice-bound
lakes. Irregularly shaped and erratically arranged hyaloclastite bodies produced at variable water levels appear to have resulted
mainly from rapid changes of the eruptive environment due to repeated build-up and drainage of ice-bound lakes as well as
the restricted space between the ice walls. We distinguish a "deep water" facies formed during high water levels of the lake,
a hydroclastic shallow water and emergent facies (leakage of the lake or growth of the volcano above the water surface). Our
model implies the temporary existence of large, stable lakes in Iceland probably formed by climatically induced ice melting.
The highly complex edifices of many table mountains and similar volcanoes were constructed during several eruptive periods
in changing environments characterized by contrasting volcanic and sedimentary processes.
Received: 10 June 1997 / Accepted: 28 July 1998 相似文献
20.
Reinhard Beer 《Icarus》1976,29(2):193-199
The “cosmic” abundance of boron is one of the least well known of all the 92 natural elements even thought it can appear in substantial concentrations on the Earth's surface. It is suggested that Jupiter might be a suitable place to search for boron because it forms numerous stable, volatile compounds with hydrogen and other abundant elements whose presence might be sought either spectroscopically or by entry devices. 相似文献