排序方式: 共有22条查询结果,搜索用时 15 毫秒
21.
Experimental metasomatism of monazite and xenotime: mineral stability, REE mobility and fluid composition 总被引:2,自引:0,他引:2
Callum J. Hetherington Daniel E. Harlov Bartosz Budzyń 《Mineralogy and Petrology》2010,99(3-4):165-184
In this study a Th-bearing monazite from a Brazil beach sand, a low Th monazite from a Malawi carbonatite, and a xenotime from a pegmatite in northern Pakistan were experimentally metasomatised in a series of common metamorphic and igneous fluids at 600°C/500 MPa and 900°C/1000 MPa. Fluids included H2O, NaCl, and KCl brines, CaF2?+?H2O, 1m and 2m HCl, 1m and 2m H2SO4, 1m NaOH, and Na2Si2O5?+?H2O. The monazite show a variety of responses to the fluids ranging from no reaction (KCl?+?H2O) to small compositional changes and partial replacement of the monazite grain rim by Th-enriched monazite in the NaOH and (Na2Si2O5?+?H2O) experiments respectively. The other acid and brine fluids induced varying degrees of partial dissolution in the monazite and xenotime, but no compositional alteration. Partial replacement of monazite grain rims by Th-enriched monazite occurred only in the alkaline fluids as the result of a coupled dissolution-reprecipitation process. 相似文献
22.
Bartosz Lew 《Experimental Astronomy》2018,45(1):81-105
Over the last few years a number of software and hardware improvements have been implemented to the 32-m Cassegrain radio telescope located near Toruń. The 19-bit angle encoders have been upgraded to 29-bit in azimuth and elevation axes. The control system has been substantially improved, in order to account for a number of previously-neglected, astrometric effects that are relevant for milli-degree pointing. In the summer 2015, as a result of maintenance works, the orientation of the secondary mirror has been slightly altered, which resulted in worsening of the pointing precision, much below the nominal telescope capabilities. In preparation for observations at the highest available frequency of 30-GHz, we use One Centimeter Receiver Array (OCRA), to take the most accurate pointing data ever collected with the telescope, and we analyze it in order to improve the pointing precision. We introduce a new generalized pointing model that, for the first time, accounts for the rail irregularities, and we show that the telescope can have root mean square pointing accuracy at the level <?8″ and <?12″ in azimuth and elevation respectively. Finally, we discuss the implemented pointing improvements in the light of effects that may influence their long-term stability. 相似文献