The ducting of acoustic gravity waves by the thermosphere: An analytic solution     

Gerald M. Daniels 《地球物理与天体物理流体动力学》2013,107(4):359-382

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Gravitational signature of rotationally distorted Jupiter caused by deep zonal winds     

Dali Kong  Xinhao Liao  Keke Zhang  Gerald Schubert 《Icarus》2013

Both deep zonal winds, if they exist, and the basic rotational distortion of Jupiter contribute to its zonal gravity coefficients J_n for n ? 2. In order to capture the gravitational signature of Jupiter that is caused solely by its deep zonal winds, one must take into account the full effect of rotational distortion by computing the coefficients J_n in non-spherical geometry. This represents a difficult and challenging problem because the widely-used spherical-harmonic-expansion method becomes no longer suitable. Based on the model of a polytropic Jupiter with index unity, we compute Jupiter’s gravity coefficients J₂, J₄, J₆, … , J₁₂ taking into account the full effect of rotational distortion of the gaseous planet using a finite element method. For the model of deep zonal winds on cylinders parallel to the rotation axis, we also compute the variation of the gravity coefficients ΔJ₂, ΔJ₄, ΔJ₆, … , ΔJ₁₂ caused solely by the effect of the winds in non-spherical geometry. It is found that the effect of the zonal winds on lower-order coefficients is weak, ∣ΔJ_n/J_n∣ < 1%, for n = 2, 4, 6, but it is substantial for the high-degree coefficients with n ? 8.  相似文献   

Strength Behavior of Naturally Cemented Marine Clay Due to Change in Ground Water Level     

G. Gerald Moses  S. Narasimha Rao 《Marine Georesources & Geotechnology》2013,31(3):160-171

The change in strength and deformation behavior of a typical marine clay deposit formed under shallow water is presented and discussed for the conditions of changing water table. This is a costal marine clay deposit with moderate carbonates along the east coast of India. The soil samples were taken from tidal flats where the sea had receded some time back, and the behavior of this deposit had been studied for the conditions of 1976, with high water table, and for the conditions of 2001, with depleted water table. Undisturbed soil samples were taken from sheeted open test pits. Standard consolidation and triaxial shear tests were conducted. Consolidation tests conducted on the samples taken for 1976 conditions with high water contents indicate that cementation effect are erased out under moderate stresses. Beyond this stress range, it behaves like soft, normally consolidated clay. In contrast, the results obtained from samples taken during 2001, with depleted water table, clearly indicate that the soil behaves like an over-consolidated one, and the improvement in the system is due to the chemical bonding and desiccation.  相似文献   

A Tribute to William M. Kaula     

Gerald Schubert 《Celestial Mechanics and Dynamical Astronomy》2000,77(4):239-240

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Grain misorientations in partially molten olivine aggregates: an electron backscatter diffraction study     

Ulrich H. Faul  John D. Fitz Gerald 《Physics and Chemistry of Minerals》1999,26(3):187-197

In polycrystalline aggregates of olivine with mean grain sizes above 35 μm plus a low basaltic melt fraction, both wetted and melt-free grain boundaries are observed after equilibration times at high pressures and temperatures of between 15 and 25 days. In order to assess a possible dependence of the wetting behaviour on the relative orientation of neighbouring grains, a SEM based technique, electron backscatter diffraction (EBSD), is used to determine grain orientations. From the grain orientations relative orientations of neighbouring grains are calculated, which are expressed as misorientation axis/angle pairs. The distribution of misorientation angles and axes of melt-free grain boundaries differ significantly from a purely random distribution, whereas those of wetted grain boundaries are statistically indistinguishable from the random distribution. The relative orientation of two neighbouring grains therefore influences the character of their common grain boundary. However, no clustering towards special (coincident site lattice) misorientation axes is observed, with the inference that the energy differences between special and general misorientations are too small to lead to the development of preferred misorientations during grain growth. Received: 8 December 1997 / Revised, accepted: 6 April 1998  相似文献   

GPS Antenna Calibration at the National Geodetic Survey   总被引：15，自引：2，他引：13  

Gerald L. Mader 《GPS Solutions》1999,3(1):50-58

The precise point whose position is being measured when a GPS baseline is determined is generally assumed to be the phase center of the GPS antenna. However, the phase center of a GPS antenna is neither a physical point nor a stable point. For any given GPS antenna, the phase center will change with the changing direction of the signal from a satellite. Ideally, most of this phase center variation depends on satellite elevation. Azimuthal effects are only introduced by the local environment around each individual antenna site. These phase center variations affect the antenna offsets that are needed to connect GPS measurements to physical monuments. Ignoring these phase center variations can lead to serious (up to 10 cm) vertical errors. This article will describe the procedure by which the National Geodetic Survey is calibrating GPS antennas and how this information may be obtained and used to avoid problems from these antenna variations. ? 1999 John Wiley & Sons, Inc.  相似文献   

The influence of bank strength on channel geometry: an integrated analysis of some observations     

He Qing Huang  Gerald C. Nanson 《地球表面变化过程与地形》1998,23(10):865-876

Bank strength exerts a significant influence on river channel geometry, but quantification of this relationship has been limited to only a few specific circumstances. This is due to both the complex nature of bank strength and the difficulty in incorporating its influence in river channel geometry relations. In order to undertake an integrated analysis of wide-ranging field observations, this study applies a recently developed multivariate model of channel geometry. When the banks of a number of laterally stable streams are categorized on the basis of the bank sediment and vegetation, the multivariate model yields numerical indices of bank strength. Within the range of the data analysed, bank strength can produce a three-fold change in channel width and a two-fold change in depth corresponding to about a 1·6-fold change in cross-sectional area. © 1998 John Wiley & Sons, Ltd.  相似文献   

The effect of the equatorially symmetric zonal winds of Saturn on its gravitational field     

Dali Kong  Keke Zhang  Gerald Schubert  John D.Anderson 《天文和天体物理学研究(英文版)》2018,(4)

The penetration depth of Saturn’s cloud-level winds into its interior is unknown.A possible way of estimating the depth is through measurement of the effect of the winds on the planet’s gravitational field.We use a self-consistent perturbation approach to study how the equatorially symmetric zonal winds of Saturn contribute to its gravitational field.An important advantage of this approach is that the variation of its gravitational field solely caused by the winds can be isolated and identified because the leading-order problem accounts exactly for rotational distortion,thereby determining the irregular shape and internal structure of the hydrostatic Saturn.We assume that(i)the zonal winds are maintained by thermal convection in the form of non-axisymmetric columnar rolls and(ii)the internal structure of the winds,because of the Taylor-Proundman theorem,can be uniquely determined by the observed cloud-level winds.We calculate both the variation △J_n,n=2,4,6...of the axisymmetric gravitational coefficients J_n caused by the zonal winds and the non-axisymmetric gravitational coefficients △J_(nm) produced by the columnar rolls,where m is the azimuthal wavenumber of the rolls.We consider three different cases characterized by the penetration depth 0.36 R_S,0.2 R_S and 0.1 R_S,where R_S is the equatorial radius of Saturn at the 1-bar pressure level.We find that the high-degree gravitational coefficient ( J_(12)+△J_(12)) is dominated,in all the three cases,by the effect of the zonal flow with |△J_(12)/J_(12)|100%and that the size of the non-axisymmetric coefficientsdirectly reflects the depth and scale of the flow taking place in the Saturnian interior.  相似文献   

Perturbation of gene expression and steroidogenesis with in vitro exposure of fathead minnow ovaries to ketoconazole     

Perkins EJ  Garcia-Reyero N  Villeneuve DL  Martinovic D  Brasfield SM  Blake LS  Brodin JD  Denslow ND  Ankley GT 《Marine environmental research》2008,66(1):113-115

Ketoconazole is a fungicidal drug that inhibits function of cytochrome P450s in the synthesis of steroids. To examine if inhibition of P450 function affects gene expression in a dynamic manner, we conducted in vitro exposures of ovary tissue from fathead minnows (Pimephales promelas) to 0.5 microM ketoconazole to investigate effects on steroid production and gene expression over time. Expression of four key steroidogenesis genes was examined at 1, 6, and 12h of exposure. 11 beta- and 20 beta-hydroxysteroid dehydrogenases were down regulated at 1h and Cytochrome P450 17 was down-regulated at 12h, consistent with the absence of steroid production. In contrast, cytochrome P450 19A was up-regulated at 6h, indicating feedback regulation. Microarray analysis of 12h exposures indicated enrichment of biological processes involved in neurotransmitter secretion, lymphocyte cell activation, sodium ion transport, and embryonic development. These data suggest that, with the exception of cytochrome P450 19A, these steroid metabolic genes are regulated in a feed forward manner and that the effects of ketoconazole may be broader than anticipated based on the mechanism of action alone.  相似文献   

Book Review: Image Interpretation in Geology, 2nd edn,by S.A. Drury. Chapman & Hall,London, 1993. No. of pages: 283. Price: £24.95 (paperback). ISBN 0 412 4880 9     

Gerald R. Lucas 《Geological Journal》1996,31(2):198-200

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