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Butler Shearer Redfern Colhoun O'Kane Penny Morris Griffiths & Cullum 《Monthly notices of the Royal Astronomical Society》1998,296(2):379-391
The Galway/DIAS Image Sharpening Camera, TRIFFID, has been used to make observations in two colours of the centre of the post-core-collapse globular cluster M15. We present here our analysis of the photometry in B over two seasons. We have combined the complementary qualities of the HST 's high astrometric precision and TRIFFID's extended coverage and photometric precision, to perform crowded-field photometry in the innermost region of M15. Our technique virtually eliminates the problem of extreme crowding which has hitherto hampered studies of the variable star populations in globular cluster cores, and thereby provides an extension of the HST 's capability. Candidate variables detected with the HST have been confirmed and monitored over longer periods. We show that most of these are RR Lyrae stars, and that one is a short-period Type II Cepheid (the third to be discovered in M15). Our photometric study also produced evidence of a similar number of new variables. These also appear to be RR Lyrae stars, except for a possible eclipsing system. Further data from an upgraded version of TRIFFID have recently been obtained to help to refine the light curves of all these objects. 相似文献
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V. Kuhnel J. C. I. Dooge J. P. J. O'Kane R. J. Romanowicz 《Surveys in Geophysics》1991,12(1-3):221-247
Partial analysis is applied to the problem of predicting the moisture fluxes of infiltraton and evaporation at land surfaces. The discussion covers the widely different scales of the soil particle, a soil pedon, a field, a basin and a biome. It is suggested that simplified models can be used at these different scales to provide bounding solutions to the integrated behaviour of land surface fluxes of interest in linking hydrologic models and general circulation climate models. 相似文献
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A mathematically transparent model for long-term solute dynamics, based on an oscillating reference frame, is applied to the
analysis of the mixing process in estuaries. Classical tidally-averaged transport models for estuaries, all derived in some
way from the Fractional Freshwater Method of Ketchum (1951) are reinterpreted in this framework. We demonstrate that in these
models, the dispersion coefficients obtained from salinity profiles are not always a good representation of the mixing intensity
of other dissolved constituents. In contrast, the hypothesis of equal coefficients is always verified in our oscillating coordinate
system, which is almost devoid of tidal harmonics. The mathematical representation of the seaward boundary condition is also
investigated. In the tidally-averaged Eulerian models, a fixed Dirichlet boundary condition is usually imposed, a condition
that corresponds to an immediate, infinite dilution of the dissolved constituent beyond the fixed estuarine mouth. This mathematical
representation of the estuarine-coastal zone interface at a fixed location is compared with the case of an oscillating location,
which protrudes back and forth into the sea with the tide. Results demonstrate that the mathematical representation of the
seaward boundary condition has a significant influence on the resulting mixing curves. We also show how to apply our approach
to the prediction of mixing curves in real estuaries. 相似文献
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Charles M. Onasch William M. Dunne Jennie E. Cook Allyson O'Kane 《Journal of Structural Geology》2009,31(9):960
Previous studies [O'Kane, A., Onasch, C.M., Farver, J., 2007. The role of fluids in low-temperature, fault-related deformation of quartz arenite. Journal of Structural Geology 29, 819--836; Cook, J., Dunne, W.M., Onasch, C.M., 2006. Development of a dilatant damage zone along a thrust relay in a low-porosity quartz arenite, Journal of Structural Geology 28, 776–792] found that quartz arenite within two fault zones in the Appalachian foreland thrust belt displays very different structural styles and histories despite deforming at similar pressures and temperatures during the Alleghanian orogeny. A comparison of the grain-scale deformation and fluid histories using transmitted and cathodoluminescence microscopy and fluid inclusion microthermometry, shows that fluid composition was a controlling factor for causing these differences. The Cove fault zone deformed in the presence of aqueous fluids, first a CaCl2 brine and then an iron-rich fluid. The precipitation of quartz cement from the brine kept pace with brittle deformation, maintaining overall rock cohesion in the fault zone. The introduction of iron-rich fluids caused a switch from precipitation to dissolution of quartz, along with precipitation of goethite. In a damage zone along a backthrust in the Cave Mountain anticline, early deformation occurred in the presence of an aqueous fluid from which quartz was precipitated. The latest deformation, however, occurred in the presence of a methane-rich fluid, which inhibited the precipitation of quartz cement producing porous breccias and open fractures despite deformation at 6 km depth. Fluid composition not only affected cementation in the fault zones, but also the selection of grain-scale deformation mechanisms. Therefore, it is a controlling factor in determining the behavior and strength of these fault zones. 相似文献
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The purpose of this paper is to validate a new method that can be used by offshore platform designers to estimate the added mass and hydrodynamic damping coefficients of potential Tension Leg Platform hull configurations. These coefficients are critical to the determination of the platform response particularly to high frequency motions in heave caused by sum-frequency wave forcing i.e. “springing”. Previous research has developed the means by which offshore platform designers can extrapolate anticipated full-scale hydrodynamic coefficients based on the response of individual model scale component shapes. The work presented here further evaluates the component scaling laws for a single vertical cylinder and quantifies the effects due to hydrodynamic interaction. Hydrodynamic interaction effects are established through a direct comparison between the superposition of individual hull component coefficients and those evaluated directly from complete hull configuration models. The basis of this comparison is established by the experimental evaluation of the hydrodynamic coefficients for individual hull components as well as partial and complete platform models. The results indicate that hydrodynamic interaction effects between components are small in heave, and validate component scaling and superposition as an effective means for added mass and damping coefficient estimation of prototype platforms. It is found that the dependency of damping ratio with KC for a TLP is almost identical to that of a single column, thus offering a scaling methodology for prototype damping ratio values. 相似文献
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