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281.
The latest eruption of Haruna volcano at Futatsudake took placein the middle of the sixth century, starting with a Plinianfall, followed by pyroclastic flows, and ending with lava domeformation. Gray pumices found in the first Plinian phase (lowerfall) and the dome lavas are the products of mixing betweenfelsic (andesitic) magma having 50 vol. % phenocrysts and maficmagma. The mafic magma was aphyric in the initial phase, whereasit was relatively phyric during the final phase. The aphyricmagma is chemically equivalent to the melt part of the phyricmafic magma and probably resulted from the separation of phenocrystsat their storage depth of 15 km. The major part of the felsicmagma erupted as white pumice, without mixing and heating priorto the eruption, after the mixed magma (gray pumice) and heatedfelsic magma (white pumice) of the lower fall deposit. Althoughthe mafic magma was injected into the felsic magma reservoir(at 7 km depth), part of the product (lower fall ejecta) precedederuption of the felsic reservoir magma, as a consequence ofupward dragging by the convecting reservoir of felsic magma.The mafic magma injection made the nearly rigid felsic magmaerupt, letting low-viscosity mixed and heated magmas open theconduit and vent. Indeed the lower fall white pumices preservea record of syneruptive slow ascent of magma to 2 km depth,probably associated with conduit formation. KEY WORDS: high-crystallinity felsic magma; magma plumbing system; multistage magma mixing; upward dragging of injected magma; vent opening by low-viscosity magma 相似文献
282.
Applying the infinite Prandtl number approximation, a semi-analytical solution for computing 2-D axisymmetric viscous Stokes flow in a model consisting of two eccentrically nested spheres of different viscosities is derived. Since numerical codes based on spectral or finite techniques for modelling mantle flow in a spherical geometry in the presence of lateral viscosity variation are becoming more and more popular, reliable examples for testing and validating such codes are extremely useful. The eccentrically nested sphere solution was used to test a numerical algorithm based on a mixed spherical-harmonic finite-element formulation of the Stokes problem, and good agreement was obtained. 相似文献
283.
284.
开放式层次化物理实验教学体系网络管理平台建设 总被引:2,自引:0,他引:2
开放式层次化物理实验教学系统的建立和运行需要一个功能强大的网络管理平台支持和保障.介绍了开放式层次化的物理实验教学体系内涵,重点介绍其网络管理平台的设计、功能、使用效果和应用前景. 相似文献
285.
J.?Miku?kaEmail author R.?Pa?teka J.?Mrlina I.?Maru?iak 《Studia Geophysica et Geodaetica》2008,52(3):381-396
We analyzed the gravitational effect of topography and bathymetry beyond the angular distance of approximately 1.5 degrees
(referred to as the distant relief effect or DRE), and its impact on measured gravity values in the region of the former Czechoslovakia.
Our work was strongly motivated by the contents of the pioneering contribution of outstanding Czech geophysicists Miloš Pick,
Jan Pícha and Vincenc Vyskočil, which appeared at the turn of the 1950’s and 1960’s. Our numerical calculations were based
upon the direct evaluation of the gravitational effects of compartments of a spherical layer, while the respective heights
and depths were obtained from the 2 × 2 minutes digital elevation model (DEM) ETOPO2, taking into consideration also the influence
of distant bathymetry. Our results are in close agreement with, but not identical to, those of the above cited authors. We
also analyzed the influence of the grid cell size of the involved DEM upon the calculation results. We introduced an approximation
of the analyzed effect, based on a simple linear relationship between the calculation point height, the DRE and its vertical
gradient (VGDRE). Since when calculated at zero elevation the involved quantities DRE and VGDRE are smooth functions of latitude
and longitude and can be easily interpolated, the approximation gives acceptable results in terms of desired accuracy of several
μGal (1 μGal = 10−8 m/s2). In general, we can state that within the territories of the Czech and Slovak Republics the studied distant relief effect
has negligible impact upon local gravity survey data. However, when applied to regional gravity studies, there could be a
question of its possible influence in the form of a quasilinear W-E trend ranging approximately from −106.6 to −102.5 mGal
within the territory of former Czechoslovakia. If we wanted to correct for this phenomenon, we should subtract this negative
quantity from the standard Bouguer anomalies as they have been defined in the recent geophysical literature, thereby considerably
increasing their values. But, instead of straightforward correcting the Bouguer anomalies for DRE only, we would rather recommend
to wait until after the crustal and even lithospheric effects have been studied more carefully based upon the present day
independent knowledge about the deep seated sources of those effects. 相似文献
286.
Non-longitudinal drifts of the Earth's magnetic field 总被引:1,自引:0,他引:1
Juliusz A. Ostrowski 《Geophysical Journal International》1988,92(1):149-163
287.
288.
289.
Fourier transform summation of Legendre series and D-functions 总被引:4,自引:1,他引:3
T. Risbo 《Journal of Geodesy》1996,70(7):383-396
The relation between D- and d-functions, spherical harmonic functions and Legendre functions is reviewed. Dmatrices and irreducible representations of the rotation group O(3) and SU(2) group are briefly reviewed. Two new recursive methods for calculations of D-matrices are presented. Legendre functions are evaluated as part of this scheme. Vector spherical harmonics in the form af generalized spherical harmonics are also included as well as derivatives of the spherical harmonics. The special dmatrices evaluated for argument equal to/2 offer a simple method of calculating the Fourier coefficients of Legendre functions, derivatives of Legendre functions and vector spherical harmonics. Summation of a Legendre series or a full synthesis on the unit sphere of a field can then be performed by transforming the spherical harmonic coefficients to Fourier coefficients and making the summation by an inverse FFT (Fast Fourier Transform). The procedure is general and can also be applied to evaluate derivatives of a field and components of vector and tensor fields. 相似文献
290.
丁世荣 《地球科学与环境学报》1998,20(2):2
对于时谐电磁场,推导出求解矢位的球面波函数展开式,应用该展开式可计算电流分布区域外部和内部的时谐电磁场,给出了用文中公式求解时谐电磁场的具体例子。 相似文献