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排序方式: 共有87条查询结果,搜索用时 15 毫秒
31.
A regional analysis of the anisotropy of the magnetic susceptibility on low-grade metamorphic, chloritoid-bearing slates of the Paleozoic in Central Armorica (Brittany, France) revealed very high values for the degree of anisotropy (up to 1.43). Nonetheless, high-field torque magnetometry indicates that the magnetic fabric is dominantly paramagnetic. Chloritoid's intrinsic degree of anisotropy of 1.47 ± 0.06, suggests that chloritoid-bearing slates can have a high degree of anisotropy without the need of invoking a significant contribution of strongly anisotropic ferromagnetic (s.l.) minerals. To validate this assumption we performed a texture analysis on a representative sample of the chloritoid-bearing slates using hard X-ray synchrotron diffraction. The preferred orientation patterns of both muscovite and chloritoid are extremely strong (∼38.6 m.r.d. for muscovite, 20.9 m.r.d. for chloritoid) and display roughly axial symmetry about the minimum magnetic susceptibility axis, indeed suggesting that chloritoid may have a profound impact on the magnetic fabric of chloritoid-bearing rocks. However, modeling the anisotropy of magnetic susceptibility by averaging single crystal properties indicates that the CPO of chloritoid only partially explains the slate's anisotropy. 相似文献
32.
Valentina Vanghi Andrea Borsato Silvia Frisia Daryl L. Howard Gertruida Gloy John Hellstrom Petra Bajo 《Sedimentology》2019,66(7):2661-2685
Synchrotron high‐resolution and micro‐X‐ray fluorescence elemental mapping of two coeval coralloid speleothems from Lamalunga Cave (Italy) are complemented with petrographic, morphological and microstratigraphic studies. The importance of these speleothems relies on their direct and indirect association with a complete Neanderthal skeleton (‘Altamura Man’) found inside the cave. The coralloids grew discontinuously between 64·6 ka and the Holocene and reveal exceptionally high concentrations of Mg, Sr and Si, particularly on convex surfaces, where evaporation is more intense. The incorporation of trace elements depends on several factors including location, shape and geometrical evolution during their growth, as well as climate and environmental parameters. This resulted in calcite precipitation with Sr compositions from 100 to 1200 ppm and an average concentration of 7000 ppm Mg. An unusually high Si content (up to 16%) is possibly derived from volcanic ash transported as particulate and in solution inside the cave. The most common fabrics observed consist of non‐fluorescent elongated columnar calcite forming clean isopachous bands and fluorescent fibre‐like crystals associated with laminated, lenticular bands high in Sr, Mg and Si. Variability in Sr, Mg and Si concentrations appears to induce fabric changes in the coralloids. Elongation and lattice distortion of the crystals was found to coincide with high Mg concentrations. The transition from compact elongated to open to fibre‐like, is here interpreted as due to high concentrations of Si and Sr, which are preferentially incorporated in the speleothem at crystal boundaries and intra‐laminae. It is here inferred that coralloid fabric changes and their elemental content potentially record local rainfall variations through time, with the clean compact calcite marking high infiltration and open fibre‐like and micrite fabrics recording dry periods. 相似文献
33.
利用同步辐射能量色散X射线衍射(EDXD)方法和金刚石对顶砧(DAC)高压技术对采于四川平武的锡石进行原位高压(达24.0 GPa)结构研究发现:压力加载过程中,锡石在13.8 GPa时发生了从金红石型结构(P 42/m nm)到C aC l2型结构(P nnm)的位移式相变;在19.9 GPa时又由C aC l2型结构相变为黄铁矿型结构(P a3),此相变为重构式相变。对于第Ⅳ主族元素氧化物(S iO2,G eO2,SnO2和PbO2)及过渡金属氧化物(M nO2和R uO2)的高压行为进行了讨论,它们具有相似的高压相变序列,这些成果对与斯石英同构氧化物的高压行为研究提供了有价值的参考。 相似文献
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35.
应用同步辐射技术解析黄色-红色石英质玉石中的致色矿物 总被引:1,自引:1,他引:0
质地细腻、颜色多彩的隐晶质-微粒脉石英在我国珠宝行业称为石英质玉石,颜色是石英质玉石价值判断的主要因素之一,揭示其致色矿物及致色机理对于研究石英质玉石的颜色评价指标和矿床成因具有重要意义,但前人并未直接获得致色矿物的准确信息。本文运用上海光源(SSRF)BL15U1线站的同步辐射硬X射线,使用μ-XRF和μ-XRD技术对黄色和红色隐晶质-微粒脉石英中的致色矿物进行了研究。结果表明,黄色石英质玉石由赋存于石英颗粒间或微裂纹中的针铁矿(特征衍射峰0.49574、0.41594、0.26887、0.25705、0.25189、0.24510、0.21806、0.17133 nm)或其集合体致色,红色石英质玉石由赋存于石英颗粒间或微裂纹中的赤铁矿(特征衍射峰0.36774、0.27091、0.25200 nm)或其集合体致色,黄色-红色石英质玉的颜色由针铁矿和赤铁矿共同致色,赤铁矿的显色能力要高于针铁矿。本文获得了石英质玉石中致色矿物的直接数据,为玉石结晶温度与致色机理的探讨、石英质玉石的品质评价提供了依据。 相似文献
36.
37.
利用同步辐射X射线荧光技术,对人工合成金刚石以及产自山东、辽宁、湖南的天然金刚石进行了微量元素的测试分析。结果表明,在合成金刚石中,检测到了第四周期的元素(除As、Ge、Kr和Br外)和Pb;其中Fe、Co、Ni相对含量高,可能是合成时触媒的混入引起的。天然金刚石中检测到的微量元素有Ca、Ti、Cr、Mn、Fe、Co、Ni、Cu、Zn、W、Au和Pb,但相对含量比合成金刚石中相应的微量元素相对含量低。不同产地的天然金刚石中的微量元素种类及含量存在差异,反映了金刚石地幔生长环境的不同及岩浆对金刚石生长过程的影响。 相似文献
38.
By now there is no doubt that the gamma-ray bursts (GRB) have a cosmological origin. This allows to regard GRB as the most
powerful known energy sources, ε∼ 1054 erg (with a total number of gamma quanta N_γ∼ 1060). A plausible mechanism of coherent synchrotron radiation (CSR) of relativistic electrons driven by a local magnetic field
is studied in this paper. We consider relativistic electrons arising in the Compton scattering of a GRB in directions close
to that of the ray from the source to a ground-based observer. The synchrotron pulses from Compton electrons located at different
points on the line between the GRB source and the observer arrive at the observation point simultaneously. This simultaneity
ensures the coherence of the detected radiation. Both molecular clouds in the host galaxy of the GRB and our own Galaxy, as
well as the Earth atmosphere are assumed to be scatterers of the GRB radiation. Signals of each scatterer reach the Earth
surface, and can be detected at radio wavelengths. We estimate the characteristics of this radiation. The comparison of GRB
data with the corresponding information on CSR pulses offers a way to determine some global characteristics of the medium
between the Earth and the GRB source. 相似文献
39.
An explicit formula is developed to explore the mechanism of the synchrotron radiation by using a bi-modal loss-cone distribution function. The variation of the distribution function along the field line is modeled in detail and the evaluation of the total power in the synchrotron radiation is presented. The variance of synchrotron radiation with latitude depends on the electron anisotropy; for low anisotropy, synchrotron radiation increases with latitude and reaches a maximum at the particle mirror points; for high anisotropy, it decreases with latitude and maximizes at the equator. A bi-modal population is therefore suggested to explain the radiation intensity which peaks both at the equator and at high latitude. 相似文献
40.