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951.
On glacial time scales, the waxing and waning of the Eurasian and North American ice sheets depend largely on variations in atmospheric temperature. As global sea level is primarily determined by the volume of these ice sheets, there is a direct (yet complex) relation between global sea level and the northern hemispheric (NH) temperature. This relation is essentially represented by a model of the NH ice sheets. We use a thermomechanical ice-sheet–ice shelf–bedrock model in conjunction with an inverse method to deduce a time series of NH temperature (from 120 kyr BP until present) that is consistent with the observed global sea level record. The advantage of this method is that it provides the annual mean surface air temperature averaged over the NH continents north of 40°N. The results reveal that ice age temperatures were 4–10°C lower than today, which agrees with other temperature reconstructions. However, reconstructed temperatures are comparitively low during the early stages of the glacial, a feature that is consistent with the rapid growth of the ice sheets. The sensitivity of the results for uncertainties in precipitation rate, in observed sea level and in some other model parameters is examined to quantify the error in reconstructed temperature. During the glacial period (120–15 kyr BP), surface air temperatures in the NH (north of 40°N) were 7.2±1.5°C lower than todays (interglacial) temperatures.  相似文献   
952.
Investigation of the Pleistocene sequence of the Gediz River, Western Turkey, has revealed a record of Early Pleistocene river terraces. Eleven terraces spanning the interval from 1.67 to 1.245 million years ago (MIS 59–37) are preserved beneath basaltic lava flows. The high number of terraces over this short time period reflects high-frequency sedimentation/incision cycles preserved due to the fortuitous combination of relatively high uplift rates (0.16 mm yr−1) and progressive southwards valley migration. Comparison of this record with ODP967 from the Eastern Mediterranean Basin suggests a link between the production of terraces and obliquity-driven 41,000 year climate cycles in the Early Pleistocene.  相似文献   
953.
Kawah Putih is a summit crater of Patuha volcano, West Java, Indonesia, which contains a shallow, 300 m-wide lake with strongly mineralized acid–sulfate–chloride water. The lake water has a temperature of 26–34°C, pH=<0.5–1.3, Stot=2500–4600 ppm and Cl=5300–12 600 ppm, and floating sulfur globules with sulfide inclusions are common. Sulfur oxyanion concentrations are unusually high, with S4O62−+S5O62−+S6O62−=2400 – 4200 ppm. Subaerial fumaroles (<93°C) on the lake shore have low molar SO2/H2S ratios (<2), which is a favorable condition to produce the observed distribution of sulfur oxyanion species. Sulfur isotope data of dissolved sulfate and native sulfur show a significant 34S fractionation (ΔSO4–Se of 20‰), probably the result of SO2 disproportionation in or below the lake. The lake waters show strong enrichments in 18O and D relative to local meteoric waters, a result of the combined effects of mixing between isotopically heavy fluids of deep origin and meteoric water, and evaporation-induced fractionation at the lake surface. The stable-isotope systematics combined with energy-balance considerations support very rapid fluid cycling through the lake system. Lake levels and element concentrations show strong seasonal fluctuations, indicative of a short water residence time in the lake as well.Thermodynamic modeling of the lake fluids indicates that the lake water is saturated with silica phases, barite, pyrite and various Pb, Sb, Cu, As, Bi-bearing sulfides when sulfur saturation is assumed. Precipitating phases predicted by the model calculations are consistent with the bulk chemistry of the sulfur-rich bottom sediments and their identified mineral phases. Much of the lake water chemistry can be explained by congruent rock dissolution in combination with preferential enrichments from entering fumarolic gases or brines and element removal by precipitating mineral phases, as indicated by a comparison of the fluids, volcanic rocks and lake bed sediment.Flank springs on the mountain at different elevations vary in composition, and are consistent with local rock dissolution as a dominant factor and pH-dependent element mobility. Discharges of warm sulfate- and chloride-rich water at the highest elevation and a near-neutral spring at lower level may contain a small contribution of crater-lake water. The acid fluid-induced processes at Patuha have led to the accumulation of elements that are commonly associated with volcano-hosted epithermal ore deposits. The dispersal of heavy metals and other potentially toxic elements from the volcano via the local drainage system is a matter of serious environmental concern.  相似文献   
954.
Incoherent scatter radars measure ionosphere parameters using modified Thomson scatter from free electrons in the target (see e.g. Hagfors, 1997). The integrated cross section of the ionospheric scatterers is extremely small and the measurements can easily be disturbed by signals returned by unwanted targets. Ground clutter signals, entering via the antenna side lobes, can render measurements at the nearest target ranges totally impossible. The EISCAT Svalbard Radar (ESR), which started measurements in 1996, suffers from severe ground clutter and the ionosphere cannot be measured in any simple manner at ranges less than about 120–150 km, depending on the modulation employed. If the target and clutter signals have different, and clearly identifiable, properties then, in principle, there are always ways to eliminate the clutter. In incoherent scatter measurements, differences in the coherence times of the wanted and unwanted signals can be used for clutter cancellation. The clutter cancellation must be applied to all modulations, usually alternating codes in modern experiments, used for shorter ranges. Excellent results have been obtained at the ESR using a simple pulse-to-pulse clutter subtraction method, but there are also other possibilities.  相似文献   
955.
From early modern times until the present, Russia (temporarily extended to the USSR) had two capital cities: Moscow and Petersburg. Moscow was the original capital, it was succeeded by Petersburg from the beginning of the 18th century. From the early 20th century onward Moscow again became the capital, but it became a different kind of capital at the end of the 20th century. The paper describes the evolution of the representation of the state function in the appearance of the capital cities by way of the state buildings, the monuments, the street names. In addition it analyses the fate of the former capitals (first Moscow, then Petersburg) in terms of their symbolic functions. Petersburg originated as a capital turned to the outside emphasizing Russia's European vocation, while Moscow was at first the inward looking capital city representing the distinctive spiritual values of Russia. Changes had to do with the changes in the nature of the successive political regimes and with the changing roles of the two cities within those regimes.  相似文献   
956.
Stalin and Hitler planned major changes in the townscapes of their capital cities. These plans were part of their effort to install highly mobilized despotic regimes that needed a wide-ranging set of symbols to focus allegiance and to impress awe. These plans remained to some extent paper exercises but part of it left significant traces in the contemporary cities, particularly in Moscow. The intended changes showed similarities in their megalomania expressed in plans for a gigantic dome surrounded by a huge public square in the core of the city. There were also differences as regards the type of symbols used due to both dictotors' different roles within their regimes, the degree of didactic intent due to the nature of the commanding ideologies and the level of modernization of both countries, and the diverging versions of antimodernist building style (which they shared with many others elsewhere at the time).  相似文献   
957.
This paper characterizes late Holocene basalts and basaltic andesites at Medicine Lake volcano that contain high pre-eruptive H2O contents inherited from a subduction related hydrous component in the mantle. The basaltic andesite of Paint Pot Crater and the compositionally zoned basaltic to andesitic lavas of the Callahan flow erupted approximately 1000 14C years Before Present (14C years b.p.). Petrologic, geochemical and isotopic evidence indicates that this late Holocene mafic magmatism was characterized by H2O contents of 3 to 6 wt% H2O and elevated abundances of large ion lithophile elements (LILE). These hydrous mafic inputs contrast with the preceding episodes of mafic magmatism (from 10,600 to ∼3000 14C years b.p.) that was characterized by the eruption of primitive high alumina olivine tholeiite (HAOT) with low H2O (<0.2 wt%), lower LILE abundance and different isotopic characteristics. Thus, the mantle-derived inputs into the Medicine Lake system have not always been low H2O, primitive HAOT, but have alternated between HAOT and hydrous subduction related, calc-alkaline basalt. This influx of hydrous mafic magma coincides temporally and spatially with rhyolite eruption at Glass Mountain and Little Glass Mountain. The rhyolites contain quenched magmatic inclusions similar in character to the mafic lavas at Callahan and Paint Pot Crater. The influence of H2O on fractional crystallization of hydrous mafic magma and melting of pre-existing granite crust beneath the volcano combined to produce the rhyolite. Fractionation under hydrous conditions at upper crustal pressures leads to the early crystallization of Fe-Mg silicates and the suppression of plagioclase as an early crystallizing phase. In addition, H2O lowers the saturation temperature of Fe and Mg silicates, and brings the temperature of oxide crystallization closer to the liquidus. These combined effects generate SiO2-enrichment that leads to rhyodacitic differentiated lavas. In contrast, low H2O HAOT magmas at Medicine Lake differentiate to iron-rich basaltic liquids. When these Fe-enriched basalts mix with melted granitic crust, the result is an andesitic magma. Since mid-Holocene time, mafic volcanism has been dominated primarily by hydrous basaltic andesite and andesite at Medicine Lake Volcano. However, during the late Holocene, H2O-poor mafic magmas continued to be erupted along with hydrous mafic magmas, although in significantly smaller volumes. Received: 4 January 1999 / Accepted: 30 August 1999  相似文献   
958.
In this paper we study a one-dimensional model for oil recovery by steamdrive. This model consists of two parts: a (global) interface model and a (local) steam condensation/capillary diffusion model. In the interface model a steam condensation front (SCF) is present as an internal boundary between the hot steam zone (containing water, oil and steam) and the cold liquid zone (containing only water and oil). Disregarding capillary pressure away from the SCF, a 2× 2 hyperbolic system arises for the water and steam saturation. This system cannot be solved uniquely without additional conditions at the SCF. To find such conditions we blow up the SCF and consider a parabolic transition model, including capillary diffusion. We study in detail the existence conditions for traveling wave solutions. These conditions provide the missing matching conditions at the SCF in the hyperbolic limit. We show that different transition models yield different matching conditions, and thus different solutions of the interface model. We also give a relatively straightforward approximation and investigate its validity for certain ranges of model parameters. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
959.
960.
2 O contents, which can be attributed to the Alpine source supplying fresh, sodic plagioclase-rich material instead of the local, strongly weathered sediments. Increasing K2O/Al2O3 can be attributed to a similar decrease in degree of weathering. However, this trend is disturbed by the loss of K from clay minerals during weathering in organic-rich layers. Local high TiO2 anomalies, caused by preferential sorting and concentration, are found in most Pliocene sections, but they are absent in the Upper Pliocene and Lower Pleistocene Alpine-derived deposits. This change is probably due to a change in the energy of the fluvial system. Finally, (pyrite-) S contents drop (siderite-) Fe contents rise. Micromorphological observations indicate that the Pliocene pyrite was formed when freshwater deposits were flooded with seawater during short-term events. The decrease in S, and the increase in siderite-Fe, can be attributed to decreasing marine influence, as a result of the marine regression at the Pliocene–Pleistocene transition. Received: 28 August 1999 / Accepted: 2 November 1999  相似文献   
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