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11.
Experimental solidification of anhydrous latitic and trachytic melts at different cooling rates: The role of nucleation kinetics 总被引:1,自引:0,他引:1
Gianluca Iezzi Silvio Mollo Guido Ventura Andrea Cavallo Claudia Romano 《Chemical Geology》2008,253(3-4):91-101
Two sets of cooling experiments were run at atmospheric conditions for two anhydrous starting latitic and trachytic melts: 1) five cooling rates (25, 12.5, 3, 0.5, and 0.125 °C/min) between 1300° and 800 °C, and 2) a 0.5 °C/min cooling rate from 1300 °C with quench temperatures at 1200°, 1100°, 1000° and 900 °C. Trachytic run-products are invariably glassy. Nucleation is also suppressed in the latitic run-products at the three highest cooling rates. Conversely, in the 0.5 and 0.125 °C/min runs, latites have a crystal content of 90 vol.%. The phases are: plagioclase, clinopyroxene, glass and iron-bearing oxide (in order of abundance). The variable quench temperatures, investigated by coupling experiments with Pt wire and Pt capsule sample containers in set 2, again did not produce crystallization of trachyte, whereas latitic samples are characterized by 10 vol.% of oxides, pyroxenes and plagioclase (in order of appearance), at temperature < 1000 °C. Effects of (preferential) heterogeneous nucleation on sample holders, of superheating degree, and chemical species loss during cooling are absent for both melt compositions. The difference of solidification paths between these two silicate melts can be ascribed only to their small chemical differences. In comparison with calculated equilibrium conditions all the experimental latitic and trachytic run-products revealed strong kinetic effects, interpretable in the light of the nucleation theory. The glass-forming ability (GFA) of trachyte is higher, whereas their critical cooling rate (Rc) is lower (< 0.125 °C/min), in comparison to latitic melts (Rc > 0.5 °C/min). The experimental results carried out in this study can be applied to lava flows and domes; trachytic lavas are able to flow for longer period with respect to latitic ones in a metastable condition. Glass-rich terrestrial lavas, i.e. obsidians, can be the result of sluggish nucleation kinetics due to the relative high polymerisation of evolved silicate melts. 相似文献
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Simona Regenspurg Mashal Alawi Guido Blöcher Maria Börger Stefan Kranz Ben Norden Ali Saadat Traugott Scheytt Lioba Virchow Andrea Vieth-Hillebrand 《Environmental Earth Sciences》2018,77(13):516
After completion of an exploration well, sandstones of the Exter Formation were hydraulically tested to determine the hydraulic properties and to evaluate chemical and microbial processes caused by drilling and water production. The aim was to determine the suitability of the formation as a reservoir for aquifer thermal energy storage. The tests revealed a hydraulic conductivity of 1–2 E-5 m/s of the reservoir, resulting in a productivity index of 0.6–1 m3/h/bar. A hydraulic connection of the Exter Formation to the overlaying, artesian “Rupelbasissand” cannot be excluded. Water samples were collected for chemical and microbiological analyses. The water was similarly composed as sea water with a maximum salinity of 24.9 g/L, dominated by NaCl (15.6 g/L Cl and 7.8 g/L Na). Until the end of the tests, the water was affected by drilling mud as indicated by the high pH (8.9) and high bicarbonate concentration (359 mg/L) that both resulted from the impact of sodium carbonate (Na2CO3) additives. The high amount of dissolved organic matter (>?58 mg/L) and its molecular-weight distribution pattern indicated that residues of cellulose, an ingredient of the drilling mud, were still present at the end of the tests. Clear evidence of this contamination gave the measured uranine that was added as a tracer into the drilling mud. During fluid production, the microbial community structure and abundance changed and correlated with the content of drilling mud. Eight taxa of sulfate-reducing bacteria, key organisms in processes like bio-corrosion and bio-clogging, were identified. It can be assumed that their activity will be affected during usage of the reservoir. 相似文献
14.
ABSTRACTThere is a lack of suitable methods for creating precipitation scenarios that can be used to realistically estimate peak discharges with very low probabilities. On the one hand, existing methods are methodically questionable when it comes to physical system boundaries. On the other hand, the spatio-temporal representativeness of precipitation patterns as system input is limited. In response, this paper proposes a method of deriving spatio-temporal precipitation patterns and presents a step towards making methodically correct estimations of infrequent floods by using a worst-case approach. A Monte Carlo approach allows for the generation of a wide range of different spatio-temporal distributions of an extreme precipitation event that can be tested with a rainfall–runoff model that generates a hydrograph for each of these distributions. Out of these numerous hydrographs and their corresponding peak discharges, the physically plausible spatio-temporal distributions that lead to the highest peak discharges are identified and can eventually be used for further investigations.
Editor A. Castellarin; Associate editor E. Volpi 相似文献
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Bas van Geel Daniel C. Fisher Adam N. Rountrey Jan van Arkel Joost F. Duivenvoorden Aline M. Nieman Guido B.A. van Reenen Alexei N. Tikhonov Bernard Buigues Barbara Gravendeel 《Quaternary Science Reviews》2011,30(27-28):3935-3946
Intestinal samples from the one-month-old Siberian mammoth calf ‘Lyuba’ were studied using light microscopy and ancient DNA to reconstruct its palaeo-environment and diet. The palynological record indicates a ‘mammoth steppe’. At least some pollen of arboreal taxa was reworked, and thus the presence of trees on the landscape is uncertain. In addition to visual comparison of 11 microfossil spectra, a PCA analysis contributed to diet reconstruction. This yielded two clusters: one of samples from the small intestine and the other of large-intestine samples, indicating compositional differences in food remains along the intestinal tract, possibly reflecting different episodes of ingestion. Based on observed morphological damage we conclude that the cyperaceous plant remains and some remains of dwarf willows were originally eaten by a mature mammoth, most likely Lyuba’s mother. The mammoth calf probably unintentionally swallowed well-preserved mosses and mineral particles while eating fecal material deposited on a soil surface covered with mosses. Coprophagy may have been a common habit for mammoths, and we therefore propose that fecal material should not be used to infer season of death of mammoths. DNA sequences of trnL and rbcL genes amplified from ancient DNA extracted from intestinal samples confirmed and supplemented plant identifications based on microfossils and macro-remains. Results from different extraction methods and barcoding markers complemented each other and show the value of longer protocols in addition to fast and commercially available extraction kits. 相似文献
17.
Guido G Weigend 《Geoforum》1975,6(2):151-161
The Danube River, Europe's longest west of the Soviet Union, connects central and southeastern Europe. It flows through areas of great diversity of climates and land forms. Navigation has, in fact, been hindered by fluctuating water levels, ice, and defiles. Primarily for political reasons the river, prior to the middle of the 20th century, had never been a viable link of transportation and communication. Since the second world war, however, effective internationalization of the river, extensive navigation improvement projects, construction of dams and hydroelectric power plants, and greatly accelerated economic development in the Danube River basin in general, all point toward the river becoming one of Europe's principal axes and regional bonds. 相似文献
18.
Computations of concentrations of minor stratospheric gases using a two-dimensional model of the stratosphere are reported. The model includes Rayleigh scattering. This results in an increase in the photodissociation rate computation time by a factor of 1.5. The effect of ground albedo is assessed by comparing our results with a calculation of photolysis rates for a constant albedo with latitude. Comparison of results with a reference model including only molecular absorption are also made. The largest differences (50%) occur in NO and OH. An approximate expression for including the effects of Rayleigh scattering and surface reflectance in multi-dimensional models is suggested. 相似文献
19.
Gianluigi Di Paola Pietro Patrizio Ciro Aucelli Guido Benassai Germán Rodríguez 《Natural Hazards》2014,71(3):1795-1819
This paper presents a new method for coastal vulnerability assessment (CVA), which relies upon three indicators: run-up distance (as a measurement of coastal inundation), beach retreat (as a measurement of potential erosion), and beach erosion rate (obtained through the shoreline positions in different periods). The coastal vulnerability analysis of Sele Coastal Plain to storm impacts is examined along a number of beach profiles realized between 2008 and 2009. This particular study area has been selected due to its low-lying topography and high erosion propensity. Results are given in terms of an impact index, performed by combining the response due to coastal inundation, storm erosion, and beach erosion rate. This analysis is implemented on the basis of morphosedimentary characteristics of the beach, wave climate evaluation, and examination of multitemporal aerial photographs and topographic maps. The analysis of the final results evidences different coastal responses as a function of the beach width and slope, which in turn depend on the local anthropization level. The comparison of this method with a Coastal Vulnerability Index method evidences the better attitude of CVA index to take into account the different beach features to explain the experienced damages in specific stretches of the coastline considered. 相似文献
20.
Ferraro G Bernardini A David M Meyer-Roux S Muellenhoff O Perkovic M Tarchi D Topouzelis K 《Marine pollution bulletin》2007,54(4):403-422
Studies of operational pollution carried out by European commission - Joint Research Centre in the Mediterranean Sea for the years 1999-2004 are briefly introduced. The specific analysis of the Adriatic Sea for the same period demonstrates that this area has been characterized by a relevant number of illegal discharges from ships. After setting the historical background of the project AESOP (aerial and satellite surveillance of operational pollution in the Adriatic Sea), the content, partners and aim of the project are presented. Finally, the results of the first phase of the AESOP project are presented. The results seem very encouraging. For the first time in the Adriatic, real time detection of oil spills in satellite images and an immediate verification by the Coast Guard has been undertaken. An exploratory activity has also been carried out in collaboration with the University of Ljubljana to use automatic information system (AIS) to identify the ships detected in the satellite images. 相似文献