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61.
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It is shown that even very slightly ionized clouds of matter and anti-matter can interpenetrate only a little on collision. Initial interpenetration produces fast electrons and positrons from annihilation. These, in turn, produce strong magneto-hydrodynamic shocks which give the small ionized component enough energy to ionize the neutral fraction and produce a Leidenfrost layer in about ten years after which interpenetration stops.  相似文献   
63.
Airborne infrared and synthetic aperture radar imagery collected over the Gulf Stream are used to examine the surface patterns of small-scale thermal convection and wind-driven Langmuir circulation. These patterns have a thermal contrast of ~0.25 °C, which is roughly an order of magnitude larger than predicted by large-eddy simulations but consistent with the effect on surface temperature of surfactant accumulations induced by mixed-layer eddies.  相似文献   
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We present a model that simulates the growth of a metropolitan area on a 2D lattice. The model is dynamic and based on microeconomics. Households show preferences for nearby open spaces and neighbourhood density. They compete on the land market. They travel along a road network to access the CBD. A planner ensures the connectedness and maintenance of the road network. The spatial pattern of houses, green spaces and road network self-organises, emerging from agents individualistic decisions. We perform several simulations and vary residential preferences. Our results show morphologies and transition phases that are similar to Dieletric Breakdown Models (DBM). Such similarities were observed earlier by other authors, but we show here that it can be deducted from the functioning of the land market and thus explicitly connected to urban economic theory.  相似文献   
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Geoffrey D. Gooch 《Geoforum》1995,26(4):429-443
For most people, both in the West and the former Soviet empire, the mass media is an important source of information about the environment, but little has been known about the ways in which environmental issues are treated in the mass media in the former communist states of East Europe. In this paper, articles dealing with environmental issues in the Estonian and Latvian press during 1992 and 1993 were analysed, and the type of problems dealt with in the articles, the sources of information used and the locations of the places referred to were examined. The results of this study show that a majority of the articles in the Estonian and Latvian press were concerned with environmental issues that were concentrated in a few places within these countries, and that when international issues were treated, these were localized to nearby European countries. Despite the existence of problems with air pollution, especially in the north-east of Estonia, these were seldom mentioned in the press. The main sources of information used in the articles were the authorities.  相似文献   
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Assessing nitrogen dynamics in the estuarine landscape is challenging given the unique effects of individual habitats on nitrogen dynamics. We measured net N2 fluxes, sediment oxygen demand, and fluxes of ammonium and nitrate seasonally from five major estuarine habitats: salt marshes, seagrass beds (SAV), oyster reefs, and intertidal and subtidal flats. Net N2 fluxes ranged from 332?±?116 μmol?N-N2?m?2?h?1 from oyster reef sediments in the summer to ?67?±?4 μmol?N-N2?m?2?h?1 from SAV in the winter. Oyster reef sediments had the highest rate of N2 production of all habitats. Dissimilatory nitrate reduction to ammonium (DNRA) was measured during the summer and winter. DNRA was low during the winter and ranged from 4.5?±?3.0 in subtidal flats to 104?±?34 μmol?15NH 4 + ?m?2?h?1 in oyster reefs during the summer. Annual denitrification, accounting for seasonal differences in inundation and light, ranged from 161.1?±?19.2 mmol?N-N2?m?2?year?1 for marsh sediments to 509.9?±?122.7 mmol?N-N2?m?2?year?1 for SAV sediments. Given the current habitat distribution in our study system, an estimated 28.3?×?106?mol of N are removed per year or 76 % of estimated watershed nitrogen load. These results indicate that changes in the area and distribution of habitats in the estuarine landscape will impact ecosystem function and services.  相似文献   
69.
The Dublin Gulch intrusion is a member of the Tombstone plutonic suite, a linear belt of middle Cretaceous intrusions that extend across the Yukon Territory. Like many of the intrusions in this suite, the Dublin Gulch intrusion is associated with several different zones of gold and tungsten mineralization, within and immediately adjacent to the intrusion. The Eagle zone (50.3 Mt @ 0.93 g/t gold), located in the southwestern part of the Dublin Gulch intrusion, hosts the most significant concentration of gold in the area. The gold occurs in a broadly east-west-striking, steeply south-dipping series of sheeted veins. The veins consist of early quartz-scheelite-pyrrhotite-pyrite-arsenopyrite, and are associated with K-feldspar-albite alteration envelopes. These grade out to and are overprinted by sericite-carbonate-chlorite alteration. The same assemblage also occurs in veinlets that refracture sheeted quartz veins and contain the majority of the gold. The gold occurs with molybdenite, lead-bismuth-antimony sulfosalts, galena, and bismuthinite. Gold correlates strongly with bismuth (r2=0.9), a relationship common to several intrusion-related gold deposits, but has a poor correlation with all other elements. Tungsten and molybdenum have a weak inter-element correlation (r2=0.55) and paragenetically pre-date the majority of gold precipitation. Lead, zinc, copper, silver, antimony, and arsenic have moderate to strong inter-element correlations (0.58 to 0.93). The change from tungsten-bearing mineralization through to gold-bismuth-rich ores with elevated syn- to post-ore lead, zinc, copper, silver, antimony, and arsenic can be grossly correlated with a change in hydrothermal fluid composition. Early scheelite-bearing quartz contains primary CO2-rich fluid inclusions, which are post-dated by secondary inclusions with higher salinities (up to 15 wt% NaCl equiv.) and less CO2. These latter inclusions are interpreted to coincide with the later gold-bismuth and base metal mineralization. The favored genetic model is one in which early CO2-rich fluids exsolved from a magma with an initially high CO2 content, but progressively became more saline and H2O-rich as the system evolved.  相似文献   
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