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121.
During March 20, 1993, from 12:00 to 16:00 UT, repeated radio burst activity was observed in the 0.8–1.2 GHz frequency range. Periods in intervals 0.1–0.5, 0.7–1.0, 2.8–3.9, 75–170 s, and 15–25 min were recognized. This long-lasting narrowband activity consisted mainly of pulsations and continua. In some intervals it was accompanied not only by spikes, broadband pulsations, and fibers in the 1–2 GHz frequency range, but also by type III and U burst activity at lower frequencies as well as by hard X-ray bursts. From several radio bursts, two characterized by different fine structures were selected and compared. The observed differences are explained by different distribution functions of superthermal electrons. The position of the 0.8–1.2 GHz radio source above the photosphere and the magnetic field in the fiber burst source were estimated to be 66 000–75 000 km and 120–135 G, respectively.Presented at te CESRA-Workshop on Coronal Magnetic Energy Release at Caputh near Potsdam in May 1994.  相似文献   
122.
This work examines the environmental and geochemical impact of recycled aggregate concrete produc-tion with properties representative for structural applications.The environmental influence of cement content,aggregate production,transportation,and waste landfilling is analysed by undertaking a life cycle assessment and considering a life cycle inventory largely specific for the region.To obtain a detailed insight into the optimum life cycle parameters,a sensitivity study is carried out in which supplementary cementitious materials,different values of natural-to-recycled aggregate content ratio and case-specific transportation distances were considered.The results show that carbon emissions were between 323 and 332 kgCO2e per cubic metre of cement only natural aggregate concrete.These values can be reduced by up to 17%by replacing 25%of the cement with fly ash.By contrast,carbon emissions can increase when natural coarse aggregates are replaced by recycled aggregates in proportions of 50%and 100%,and trans-portation is not included in analysis.However,the concrete with 50%recycled aggregate presented lower increase,only 0.3%and 3.4%for normal and high strength concrete,respectively.In some cases,the rel-ative contribution of transportation to the total carbon emissions increased when cement was replaced by fly ash in proportions of 25%,and case-specific transportation distances were considered.In absolute values,the concrete mixes with 100%recycled aggregates and 25%fly ash had lower carbon emissions than concrete with cement and natural aggregates only.Higher environmental benefits can be obtained when the transportation distances of fly ash are relatively short(15-25 km)and the cement replacement by fly ash is equal or higher than 25%,considering that the mechanical properties are adequate for prac-tical application.The observations from this paper show that recycled aggregate concrete with strength characteristics representative for structural members can have lower carbon emissions than conventional concrete,recommending them as an alternative to achieving global sustainability standards in construction.  相似文献   
123.
The clinopyroxene–plagioclase–plagioclase dihedralangle, cpp, in gabbroic cumulates records the time-integratedthermal history in the sub-solidus and provides a measure oftextural maturity. Variations in cpp through the Layered Seriesof the Skaergaard intrusion, East Greenland, demonstrate thatthe onset of crystallization of clinopyroxene (within LZa),Fe–Ti oxides (at the base of LZc) and apatite (at thebase of UZb) as liquidus phases in the bulk magma is recordedby a stepwise increase in textural maturity, related to an increasein the contribution of latent heat to the total heat loss tothe surroundings and a reduction in the specific cooling rateat the crystallization front of the intrusion. The onset ofboth liquidus Fe–Ti oxide and apatite crystallizationis marked by a transient increase in textural maturity, probablylinked to overstepping before nucleation. Textural maturationat pyroxene–plagioclase–plagioclase triple junctionseffectively ceases in the uppermost parts of the Layered Seriesas a result of the entire pluton cooling below the closure temperaturefor dihedral angle change, which is 1075°C. Solidificationof the Layered Series of the Skaergaard intrusion occurred viathe upwards propagation of a mush zone only a few metres thick. KEY WORDS: magma; partial melting; asthenosphere; olivine; mantle  相似文献   
124.
125.
The Seve Nappe Complex of the Scandinavian Caledonides is thought to be derived from the distal passive margin of Baltica which collided with Laurentia in the Scandian Phase of the Caledonian Orogeny at 430–400 Ma. Parts of the Seve Nappe Complex were affected by pre-Scandian high- and ultrahigh-pressure metamorphism, in a tectonic framework that is still unclear, partly due to uncertainties about the exact timing. Previous age determinations yielded between ~ 505 and ~ 446 Ma, with a general trend of older ages in the North (Norrbotten) than in the South (Jämtland). New age determinations were performed on eclogite and garnet–phengite gneiss at Tjeliken in northern Jämtland. Thermodynamic modelling yielded peak metamorphic conditions of 25–27 kbar/680–760 °C for the garnet–phengite gneiss, similar to published peak metamorphic conditions of the eclogite (25–26 kbar/650–700 °C). Metamorphic rims of zircons from the garnet–phengite gneiss were dated using secondary ion mass spectrometry and yielded a concordia age of 458.9 ± 2.5 Ma. Lu–Hf garnet-whole rock dating yielded 458 ± 1.0 Ma for the eclogite. Garnet in the eclogite shows prograde major-element zoning and concentration of Lu in the cores, indicating that this age is related to garnet growth during pressure increase, i.e. subduction. The identical ages from both rock types, coinciding with published Sm–Nd ages from the eclogite, confirm subduction of the Seve Nappe Complex in Northern Jämtland during the Middle Ordovician in a fast subduction–exhumation cycle.  相似文献   
126.
The thickness of the crystal mush on magma chamber floors can be constrained using the offset between the step-change in the median value of dihedral angles formed at the junctions between two grains of plagioclase and a grain of another phase (typically clinopyroxene, but also orthopyroxene and olivine) and the first appearance or disappearance of the liquidus phase associated with the step-change in median dihedral angle. We determined the mush thickness in the Rustenburg Layered Suite of the Bushveld Complex at clinopyroxene-in (in Lower Main Zone) and magnetite-in (in Upper Zone). We also examined an intermittent appearance of cumulus apatite in Upper Zone, using both the appearance and disappearance of cumulus apatite. In all cases, the mush thickness does not exceed 4 m. These values are consistent with field observations of a mechanically rigid mush at the bases of both magnetitite and chromitite layers overlying anorthosite. Mush thickness of the order of a few metres suggests that neither gravitationally-driven compaction nor compositional convection within the mush layer is likely to have been important processes during solidification: adcumulates in the Bushveld are most likely to have formed at the top of the mush during primary crystallisation. Similarly, it is unlikely either that migration of reactive liquids occurs through large stretches of stratigraphy, or that layering is formed by mechanisms other than primary accumulation.  相似文献   
127.
Lachhab A  Zhang YK  Muste MV 《Ground water》2008,46(6):865-872
A low-cost, noninvasive, three-dimensional (3D), particle tracking velocimetry system was designed and built to investigate particle movement in match-index-refraction porous media. Both a uniform load of the glass beads of the same diameter and a binary load of the glass beads of two diameters were used. The purpose of the experiments is to study the effect of the two loads on the trajectories, velocity distribution, and spreading of small physical particles. A total of 35 particles were released and tracked in the uniform load and 46 in the binary load. The 3D trajectory of each particle was recorded with two video camcorders and analyzed. It is found that the particle's velocity, trajectory, and spreading are very sensitive to its initial location and that the smaller pore size or heterogeneity in the binary load increases the particles' velocity and enhances their spreading as compared with the uniform load. The experiments also verified the previous finding that the distribution of the particle velocities are lognormal in the longitudinal direction and Gaussian in two transverse directions and that the particle spreading is much larger along the longitudinal direction than along the traverse directions.  相似文献   
128.
The Ballachulish Igneous Complex consists of an outer quartz diorite and an inner granite, emplaced at about 300 MPa, initially at 1000 to 1050 °C. The contact aureole (0.5–2 km wide) occurs in metapelites and metapsammites plus minor graphitic slates, carbonate rocks and metaquartzites. A textural examination of the arkosic Appin Quartzite, which was previously believed to have melted only within a few metres of the intrusion, demonstrates that partial melting occurred up to 500 m away from the vertical eastern contact. Coupling petrographic observations with Qtz-Ab-Or-H2O phase relations, we determined both the amounts of actual melt and the maximum possible amounts of melt in the samples. Melting efficiency was everywhere less than 100% and decreased with distance from the intrusion. Though perhaps not the only possible source of fluid throughout the aureole, simple models demonstrate that H2O evolution from the pluton would have been volumetrically sufficient and persisted long enough to account for the observed partial melting. A time-integrated fluid flux of 7000 kg/m2 from the pluton is necessary to account for the observed amounts of partial melt in the Appin Quartzite. From its inefficiency, we infer that infiltration of the Appin Quartzite cannot have occurred along interconnected grain-edge channels. Rather, it was controlled by hydraulic fracturing, with fracture density determining melting efficiency. Bulk-rock permeability is calculated to be 10−20 m2, an order of magnitude lower than that necessary to permit pervasive flow of all the fluid exsolving from the pluton. There is little difference between the calculated time-integrated fluid flux through the Appin Quartzite on the eastern flank and an estimate of the infiltrating flux through the pelitic Leven Schist on the western flank in the time interval during which both rock types were above their solidus temperature, despite differences in their equilibrium quartz-H2O dihedral angles at temperatures immediately below the solidus, and differences in the attitude of the contact. The rates of H2O expulsion from the cooling pluton are consistent with highly efficient fracture-dominated flow, allowing insufficient time for textural equilibration. Received: 26 March 1998 / Accepted: 8 March 1999  相似文献   
129.
Drifting pulsation structures (DPSs) are considered to be radio signatures of the plasmoids formed during magnetic reconnection in the impulsive phase of solar flares. In the present paper we analyze oscillations and waves in seven examples of drifting pulsation structures, observed by the 800?–?2000 MHz Ond?ejov Radiospectrograph. For their analysis we use a new type of oscillation maps, which give us much more information as regards processes in DPSs than that in previous analyses. Based on these oscillation maps, made from radio spectra by the wavelet technique, we recognized quasi-periodic oscillations with periods ranging from about 1 to 108 s in all studied DPSs. This strongly supports the idea that DPSs are generated during a fragmented magnetic reconnection. Phases of most the oscillations in DPSs, especially for the period around 1 s, are synchronized (“infinite” frequency drift) in the whole frequency range of DPSs. For longer periods in some DPSs we found that the phases of the oscillations drift with the frequency drift in the interval from ?17 to \(+287~\mbox{MHz}\,\mbox{s}^{-1}\). We propose that these drifting phases can be caused (a) by the fast or slow magnetosonic waves generated during the magnetic reconnection and propagating through the plasmoid, (b) by a quasi-periodic structure in the plasma inflowing to the reconnection forming a plasmoid, and (c) by a quasi-periodically varying reconnection rate in the X-point of the reconnection close to the plasmoid.  相似文献   
130.
Particulate matter from the nepheloid layer and from regions of clearer water have been examined under the light microscope to determine particle concentration, size and composition. The total count of suspended particles is a basic difference between water samples from nepheloid layers of the North American and Brazil basins, and samples from the clearer water over the Mid-Atlantic Ridge in both the North and South Atlantic. The nepheloid layer of the North American Basin has four times, and the Brazil Basin three times the particle density of clearer water over the mid-ocean ridge. A greater percentage of particles of < 2 μ size prevails in nepheloid water ranging from 85–96% as compared to a range of 76–87% in the clear water. Non-opaque mineral grains form the major constituent.  相似文献   
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