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811.
812.
813.
Calculation of electromagnetic sensitivities in the time domain 总被引:1,自引:0,他引:1
Andreas Hördt 《Geophysical Journal International》1998,133(3):713-720
The speed of calculating sensitivities for 3-D conductivity structures for time- domain electromagnetic methods is significantly improved by applying the reciprocity theorem directly in the time domain. The sensitivities are obtained by convolving the electric field in the subsurface due to a transmitter at the surface with the electric field impulse response due to another transmitter, which replaces the original receiver. The acceleration compared to the classical perturbation method is approximately P/R , where P is the number of model parameters and R is the number of receiver positions. If the sensitivity has to be calculated very close to the receiver, approximate sensitivities can be obtained using an integral condition. Comparisons with the classical perturbation approach show that the method gives accurate results. Examples using transmitter–receiver configurations from a long-offset transient electromagnetics survey demonstrate the usefulness of sensitivities for the evaluation of resolution properties. 相似文献
814.
815.
Thor H. Hansteen Andreas Klügel Hans-Ulrich Schmincke 《Contributions to Mineralogy and Petrology》1998,132(1):48-64
Gabbroic and ultramafic xenoliths and olivine and clinopyroxene phenocrysts in basaltic rocks from Gran Canaria, La Palma,
El Hierro, Lanzarote and La Gomera (Canary Islands) contain abundant CO2-dominated fluid inclusions. Inclusion densities are strikingly similar on a regional scale. Histogram maxima correspond to
one or more of the following pressures: (1) minimum 0.55 to 1.0 GPa (within the upper mantle); (2) between 0.2 and 0.4 GPa
(the Moho or the lower crust); (3) at about 0.1 GPa (upper crust). Fluid inclusions in several rocks show a bimodal density
distribution, the lower-density maximum comprising both texturally early and late inclusions. This is taken as evidence for
an incomplete resetting of inclusion densities, and simultaneous formation of young inclusions, at well-defined magma stagnation
levels. For Gran Canaria, pressure estimates for early inclusions in harzburgite and dunite xenoliths and olivine phenocrysts
in the host basanites overlap at 0.9 to 1.0 GPa, indicating that such magma reservoir depths coincide with levels of xenolith
entrainment into the magmas. Magma chamber pressures within the mantle, inferred to represent levels of mantle xenolith entrainment,
are 0.65–0.95 GPa for El Hierro, 0.60–0.68 GPa for La Palma, and 0.55–0.75 GPa for Lanzarote. The highest-density fluid inclusions
in many Canary Island mantle xenoliths have probably survived in-situ near-isobaric heating at the depth of xenolith entrainment.
Inclusion data from all islands indicate ponding of basaltic magmas at Moho or lower crustal depths, and possibly at an additional
higher level, strongly suggestive of two main crustal accumulation levels beneath each island. We emphasize that repeated
magmatic underplating of primitive magmas, and therefore intrusive accretion, are important growth mechanisms for the Canary
Islands, and by analogy, for other ocean islands. Comparable fluid inclusion data from primitive rocks in other tectonic settings,
including Iceland, Etna and continental rift systems (Hungary, South Norway), indicate that magma accumulation close to Moho
depths shortly before eruption is not, however, restricted to oceanic intraplate volcanoes. Lower crustal ponding and crystallization
prior to eruption may be the rule rather than the exception, independent of the tectonic setting.
Received: 30 May 1997 / Accepted: 6 February 1998 相似文献
816.
Liquidus temperatures and phase compositions in the system Qz-Ab-Or at 5 kbar and very low water activities 总被引:1,自引:0,他引:1
Andreas Becker Francois Holtz Wilhelm Johannes 《Contributions to Mineralogy and Petrology》1998,130(3-4):213-224
Liquidus phase relations have been experimentally determined in the systems Qz-Ab-Or-(H2O), Qz-Ab-(H2O) and Qz-Or-(H2O) at H2O-undersaturated conditions (a
H2O = 0.07) and P = 5 kbar. Starting materials were homogeneous synthetic glasses containing 1 wt% H2O. The liquidus temperatures were bracketed by crystallization and dissolution experiments. The results of kinetic studies
showed that crushed glasses are the best starting materials to overcome undercooling and to minimize the temperature difference
between the lowest temperature of complete dissolution (melting) and the highest temperature at which crystallization can
be observed. At P = 5 kbar and a
H2O = 0.07, the Qz-Ab eutectic composition is Qz32Ab68 at 1095 °C (±10 °C) and the Qz-Or eutectic is Qz38Or62 at 1030 °C (±10 °C). The minimum temperature of the ternary system Qz-Ab-Or is 990 °C (±10 °C) and the minimum composition
is Qz32Ab35‐ Or33. The Qz content of the minimum composition in the system Qz-Ab-Or-H2O remains constant with changing a
H2O. The normative Or content, however, increases by approximately 10 wt% with decreasing a
H2O from 1 to 0.07. Such an increase has already been observed in the system Qz-Ab-Or-H2O-CO2 at high a
H2O and it is concluded that the use of CO2 to reduce water activities does not influence the composition of the minima in quartz-feldspar systems. The determined liquidus
temperature in melts with 1 wt% H2O is very similar to that obtained in previous nominally “dry” experiments. This discrepancy is interpreted to be due to problems
in obtaining absolutely dry conditions. Thus, the hitherto published solidus and liquidus temperatures for “dry” conditions
are probably underestimated.
Received: 27 March 1997 / Accepted: 1 October 1997 相似文献
817.
A synthesis has been undertaken based on regionally compiled data from the post early Eocene foreland basin succession of Svalbard. The aim has been to generate an updated depositional model and link this to controlling factors. The more than kilometer thick progradational succession includes the offshore shales of the Gilsonryggen Member of the Frysjaodden Formation, the shallow marine sandstones of the Battfjellet Formation and the predominantly heterolithic Aspelintoppen Formation, together recording the progressive eastwards infill of the foredeep flanking the West Spitsbergen fold‐and‐thrust belt. Here we present a summary of the paleo‐environmental depositional systems across the basin, their facies and regional distribution and link these together in an updated depositional model. The basin‐margin system prograded with an ascending shelf‐edge trajectory in the order of 1°. The basin fill was bipartite, with offset stacked shelf and shelf‐edge deltas, slope clinothems and basin floor fans in the western and deepest part and a simpler architecture of stacked shelf‐deltas in the shallower eastern part. We suggest a foredeep setting governed by flexural loading, likely influenced by buckling, and potentially developing into a wedge top basin in the mature stage of basin filling. High‐subsidence rates probably counteracted eustatic falls with the result that relative sea‐level falls were uncommon. Distance to the source terrain was small and sedimentation rates was temporarily high. Time‐equivalent deposits can be found outbound of Stappen High in the Vestbakken Volcanic Province and the Sørvestsnaget Basin 300 km further south on the Barents Shelf margin. We cannot see any direct evidence of coupling between these more southerly systems and the studied one; southerly diversion of the sediment‐routing, if any, may have taken place beyond the limit of the preserved deposits. 相似文献
818.
Andreas Ballot Stephan PflugmacherClaudia Wiegand Kiplagat KotutLothar Krienitz 《Limnologica》2003,33(1):2-9
This paper presents data on the first identification, characterization and quantification of hepatotoxic microcystins and neurotoxic anatoxin-a in water samples of Lake Baringo, Kenya. The shallow turbid Lake Baringo was investigated five times between June 2001 and May 2002. The phytoplankton community was mainly dominated by the cyanobacterium Microcystis aeruginosa. Due to the high turbidity the phytoplankton biomass was low, ranging between 1.5 and 8.2 mg L−1. High mean total phosphorus concentration (1.0 mg L−1) and mean total nitrogen concentration (2.8 mg L−1) typical for hypertrophic lakes were found. Using HPLC technique the hepatotoxins microcystin-LR, -RR and -YR and the neurotoxin anatoxin-a were detected in the water samples. The microcystin concentrations varied from 310 to 19800 μg microcystin-LR equivalents g−1 DW and the anatoxin-a concentration ranged from 270 to 1260 μg g−1 DW. To our knowledge this is the first evidence of cyanobacterial toxins in Lake Baringo. 相似文献
819.
Rolf S. Arvidson Inci Evren Ertan Andreas Luttge 《Geochimica et cosmochimica acta》2003,67(9):1623-1634
A comparison of published calcite dissolution rates measured far from equilibrium at a pH of ∼ 6 and above shows well over an order of magnitude in variation. Recently published AFM step velocities extend this range further still. In an effort to understand the source of this variation, and to provide additional constraint from a new analytical approach, we have measured dissolution rates by vertical scanning interferometry. In areas of the calcite cleavage surface dominated by etch pits, our measured dissolution rate is 10−10.95 mol/cm2/s (PCO2 10−3.41 atm, pH 8.82), 5 to ∼100 times slower than published rates derived from bulk powder experiments, although similar to rates derived from AFM step velocities. On cleavage surfaces free of local etch pit development, dissolution is limited by a slow, “global” rate (10−11.68 mol/cm2/s). Although these differences confirm the importance of etch pit (defect) distribution as a controlling mechanism in calcite dissolution, they also suggest that “bulk” calcite dissolution rates observed in powder experiments may derive substantial enhancement from grain boundaries having high step and kink density. We also observed significant rate inhibition by introduction of dissolved manganese. At 2.0 μM Mn, the rate diminished to 10−12.4 mol/cm2/s, and the well formed rhombic etch pits that characterized dissolution in pure solution were absent. These results are in good agreement with the pattern of manganese inhibition in published AFM step velocities, assuming a step density on smooth terraces of ∼9 μm−1. 相似文献
820.
AbstractDetecting and describing movement of vehicles in established transportation infrastructures is an important task. It helps to predict periodical traffic patterns for optimizing traffic regulations and extending the functions of established transportation infrastructures. The detection of traffic patterns consists not only of analyses of arrangement patterns of multiple vehicle trajectories, but also of the inspection of the embedded geographical context. In this paper, we introduce a method for intersecting vehicle trajectories and extracting their intersection points for selected rush hours in urban environments. Those vehicle trajectory intersection points (TIP) are frequently visited locations within urban road networks and are subsequently formed into density-connected clusters, which are then represented as polygons. For representing temporal variations of the created polygons, we enrich these with vehicle trajectories of other times of the day and additional road network information. In a case study, we test our approach on massive taxi Floating Car Data (FCD) from Shanghai and road network data from the OpenStreetMap (OSM) project. The first test results show strong correlations with periodical traffic events in Shanghai. Based on these results, we reason out the usefulness of polygons representing frequently visited locations for analyses in urban planning and traffic engineering. 相似文献