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排序方式: 共有210条查询结果,搜索用时 15 毫秒
111.
Energy Optimization of Well Fields 总被引:1,自引:0,他引:1
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Henrik Stendal Sadrack Flix Toteu Robert Frei Joseph Penaye Urbain Olivier Njel Jean Bassahak Jean Nni Boniface Kankeu Vincent Ngako Joseph Victor Hell 《Journal of African Earth Sciences》2006,44(4-5):443
Rutile, as an important component in alluvial or eluvial heavy mineral deposits, is known in southern Cameroon. These deposits are underlain by the Neoproterozoic low- to high-grade Yaoundé Group. Geochemical, thermometric, fluid inclusion and Pb isotopic studies of the rutile from alluvial and eluvial concentrates and from medium-grade micaschist from the nearby Yaoundé region permit the following conclusions: (1) alluvial and eluvial rutile of the Yaoundé region are derived from the degradation of metapelites, metamafic rocks and pegmatites of the nearby Yaoundé Group; (2) rutile in the Yaoundé Group formed during the Pan-African metamorphism, or was inherited as detrital rutile from a 900 Ma source. The study also shows that the rutile can be used to trace the history of the Pan-African belt north of the Congo craton. 相似文献
115.
This paper addresses the fine-scale axisymmetric structure exhibited in Saturn's A and B-rings. We aim to explain both the periodic microstructure on 150-220 m, revealed by the Cassini UVIS and RSS instruments, and the irregular variations in brightness on 1-10 km, reported by the Cassini ISS. We propose that the former structures correspond to the peaks and troughs of the nonlinear wavetrains that form naturally in a viscously overstable disk. The latter variations on longer scales may correspond to modulations and defects in the wavetrains' amplitudes and wavelength. We explore these ideas using a simple hydrodynamical model which captures the correct qualitative behaviour of a disk of inelastically colliding particles, while also permitting us to make progress with analytic and semi-analytic techniques. Specifically, we calculate a family of travelling nonlinear density waves and determine their stability properties. Detailed numerical simulations that confirm our basic results will appear in a following paper. 相似文献
116.
The Huygens entry probe descended through the atmosphere of Titan and provided an excellent set of observations of the atmosphere and the surface of Titan. During the 150-min descent the Huygens Atmospheric Structure Instrument (HASI) observed a comprehensive set of variables, including pressure, temperature, density and atmospheric electricity. The atmospheric pressure profile was recorded by the Pressure Profile Instrument (PPI), provided by Finnish Meteorological Institute (FMI). The instrument started measurements at an altitude of 150 km, and produced about 28 bits of data per second. Data were also obtained through the time of 31 min beyond the time of surface impact. The first-order scientific analysis of the PPI results has been performed. The observations together with hydrostatic assumption and in combination with other measurements have provided the first atmospheric pressure profile and the surface pressure (of approximately ) for Titan's atmosphere. To carry out the pressure profile reconstruction we developed a real gas formulation, which is applicable also for other Titan atmospheric investigations. The altitude versus time speed of the descent was calculated and the results were compared with the direct altitude observations by the radar altimeter during the last 40 km of the descent. The fit was excellent demonstrating the high-quality level of the PPI observations as well as the utilized investigation methods. 相似文献
117.
We discuss various strategies for parallelizing streamline simulators and present a single-phase shared memory implementation.
The choice of a shared memory programming model is motivated by its suitability for streamline simulation, as well as the
rapid advance of multicore processors, which are readily available at low-cost. We show that streamline-based methods are
easily parallelizable on shared memory architectures through their decomposition of the multidimensional transport equations
into a large set of independent 1D transport solves. We tested both a specialized explicit load balancing algorithm that optimizes
the streamline load distribution across threads to minimize the time that any of the threads are idle, and the dynamic load
balancing algorithms provided by OpenMP on the shared memory machines. Our results clearly indicate that built-in schedulers
are competitive with specialized load balancing strategies as long as the number of streamlines per thread is sufficiently
high, which is the case in field applications. The average workload per thread is nominally insensitive to workload variations
between individual streamlines, and any load balancing advantage offered by explicit strategies is not sufficient to overcome
associated computational and parallel overhead. In terms of the allocation of streamlines or streamline segments to threads,
we investigated both the distributed approach, in which threads are assigned streamline segments, and the owner approach,
in which threads own complete streamlines. We found that the owner approach is most suitable. The slight advantage that the
distributed approach has in terms of load balancing is not enough to compensate for the additional overheads. Moreover, the
owner approach allows straightforward re-use of existing sequential codes, which is not the case for the distributed approach
in case of implicit or adaptive implicit solution strategies. The tracing and mapping stages in streamline simulation have
low parallel efficiency. However, in real-field models, the computational burden of the streamline solves is significantly
heavier than that of the tracing and mapping stages, and therefore, the impact of these stages is limited. We tested the parallelization
on three shared memory systems: a 24 dual-core processor Sun SPARC server; an eight-way Sun Opteron server, representative
of the state-of-the-art shared memory systems in use in the industry; and the very recently released Sun Niagara II multicore
machine that has eight floating point compute units on the chip. We test a single-phase flow problem on three heterogeneous
reservoirs with varying well placements (this system gives the worst case scenario as the tracing and mapping costs are not
negligible compared to the transport costs). For the SPARC and Opteron system, we find parallel efficiencies ranging between
60 and 75 for the tracer flow problems. The sublinear speedup is mostly due to communication overheads in the tracing and
mapping stages. In applications with more complex physics, the relative contributions of these stages will decrease significantly,
and we predict the parallel performance to be nearly linear. On the Niagara II, we obtain almost perfect linear scalability
even for the single-phase flow problem thanks to the lowered communication costs on these architectures that have a shared
cache. This result is all the more satisfactory considering that future server designs will be akin to this system. 相似文献
118.
Lucas R.D. Jensen Henrik Friis Erling Fundal Per Møller Mads Jespersen 《Engineering Geology》2010,110(3-4):43-50
Four dense Scandinavian limestones were analyzed to determine their mechanical properties. The generation of dust (? 10 μm) and fines (? 90 μm) during a closed circuit vertical roller mill comminution process was correlated with the calcite crystal size distributions of each limestone. Thin sections were analyzed and by means of stereology the calcite crystal size distributions for each limestone was measured. The dust generation of limestones is governed by a surface abrasive mechanism (R2 = 0.99) and the production of fines is governed by the mechanical strength of limestones (R2 = 0.99). The overall limestone degradation mechanism is predominantly controlled by the calcite cleavage planes which reduce the power consumption during the comminution process. This study is the first step in determining the influence of limestone texture on the wear rates in heterogenous raw mixes used in closed circuit comminution equipment. 相似文献
119.
Hassane El Mkami Henrik Friis Adrian A. Finch G. M. Smith 《Physics and Chemistry of Minerals》2010,37(8):519-528
The location and coordination of Mn2+ paramagnetic luminescent centres in three natural samples of leucophanite (ideally, NaCaBeSi2O6F) have been investigated by electron paramagnetic resonance (EPR) and electron spin-echo envelope modulation (ESEEM) spectroscopy.
Continuous wave (cw)-EPR was carried out at multiple frequencies (9, 94 and 188 GHz) which allowed the precise determination
of the spin Hamiltonian parameters. The simulation of the cw-EPR spectra shows that the signal originates from one manganese
located in a single distorted site. This distortion was close to axial symmetry with a slight rhombicity and was consistent
with an eight coordinated Mn2+ substituting for Ca2+. Spectral differences between the samples could be attributed mainly to D-strain effect. Three-pulse ESEEM spectroscopy was
also used to investigate the coordination environment of the manganese and showed weak coupling between the manganese and
beryllium (9Be), sodium (23Na) and fluorine (19F) nuclei in the second and subsequent coordination spheres. The Mn ligand distances estimated from the ESEEM data are in
good agreement with bond distances estimated from X-ray diffraction data. To our best knowledge, only few ESEEM studies have
been reported so far in Earth science and this is believed to be the first detailed ESEEM study of Mn2+ in a natural mineral system. 相似文献
120.