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991.
矿物和玻璃中MgK-边X射线吸收光谱研究 总被引:1,自引:1,他引:0
我们利用同步辐射X射线吸收光谱已经研究了硅酸盐矿物、铝硅酸盐矿物和玻璃中的主要阴离子Si、AlK边X射线吸收光谱[1~5],指出随着压力变化而引起Si、AlK边向高能位移而配位数增大的规律。硅由4配位(如石英)变成6配位(如柯石英)。Al在矿物结构中的配位不同,如4配位的蓝晶石、5配位的红柱石、6配位的矽线石。这些矿物的局部结构不同,其键长、键角也不同,从而引起矿物的物理性质发生明显的变化。Mg不仅是地壳中广泛分布的造岩元素,而且也是组成地幔物相和未分异的原始岩浆的主要成分,是组成造岩矿物的… 相似文献
992.
Katja Henjes 《Boundary-Layer Meteorology》1999,91(3):367-384
For an extensive turbulent wind speed data set collected on the open ocean, the optimum sampling time is determined to calculate inertial-range spectra. Such spectra are widely used to estimate surface fluxes. The optimum sampling time corresponds to the turbulent memory time, the minimum period after which a given time series can be interpreted as a new independent measurement. In our case, this interval is found to be only about six seconds.Separate spectral levels are calculated from the three measured vector components of the wind. Their ratios are compatible with the assumption of an isotropic inertial subrange, but scatter considerably. Alignment factors are developed based on Kolmogorov's theory, and the aligned spectral levels coincide within a few percent. It is proposed that alignment might be a more reliable test than the ratio of the spectral levels to determine whether observations have taken place in a universal inertial subrange. It is recommended that all three wind components are used to estimate the dissipation rate. 相似文献
993.
实际雨滴谱微波辐射与衰减特征 总被引:1,自引:0,他引:1
对500份不同雨型雨滴谱谱进行分析,建立了Z-I、kt-I、ka-I、L-I等20各雨滴谱微波辐射特征量与雨滴谱本身特征量之间的统计模式,得到了一些有意义的结果。它在大气、信息等学科中有一定应用价值。 相似文献
994.
995.
M. N.?TaranEmail author A. N.?Tarashchan H.?Rager St.?Schott K.?Schürmann W.?Iwanuch 《Physics and Chemistry of Minerals》2003,30(9):546-555
Variously colored gem-quality topazes from Ouro Preto, Minas Gerais, Brazil, were studied by optical absorption spectroscopy and photoluminescence methods. In the near infrared range (750–2500 nm) the absorption spectra display an identical pattern of narrow intense absorption lines caused by overtones and combination vibrations of OH groups, which do not relate to the coloration of the topazes studied. Their colors were found to be caused by combination of three sets of absorption features, (1), (2), and (3) in the visible and near-UV range, which are due to different color center. (1) denotes a pair of broad split bands with maxima 18 000 and 25 000 cm–1 caused by electronic spin-allowed dd transitions of Cr3+ ions. They cause a light rose to deep violet color and characteristic pleochroism of Cr3+-containing topazes. Photoluminescence evidences of at least three different types of Cr3+ complexes which, most probably, differ by ligand surroundings, O4F2, O4F(OH) and O4(OH) (2) Corresponds to the intense weakly polarized UV absorption edge. Two different parts, the thermally stable one, caused by ligand-to-metal charge transfer, and the thermally unstable one, caused by some defect center(s), contribute to the edge. (3) denotes a system of two broad unstructured bands with maxima around 19 000 cm–1 (X>Y Z) and 24 000 cm–1 (Y Z
X). They cause the unique orange color and characteristic pleochroism of Brazilian Imperial topazes. Combinations of (1) and (3) absorption features cause various yellow-rose colors of the samples. Investigations of natural irradiated and thermally treated topazes show that the color centers (1) and (3) transform to each other at annealing and X- or gamma irradiation. The color of natural orange-red Imperial topazes is assumed to be caused by Cr4+, stabilized by other impurity ions and/or defect irradiation EPR centers. At T=300 °C Cr4+ reduces to Cr3+, the color of Imperial topazes changes to pale rose, caused by spin-allowed bands of Cr3+. In artificially irradiated crystals the (3)-center, Cr4+, may be induced according to the reaction 2Cr3+ Cr4+ + Cr2+, which involves chromium pairs in adjacent Al sites of the structure. Such artificially induced color is unstable at room temperature and in daylight. The process of the decay of (3)-centers may be described as a recombination Cr4++Cr2+ 2Cr3+ that results in vanishing of the (3)-bands accompanied by the appearance or increase in Cr3+
dd bands, the original orange color turning to a pale rose. 相似文献
996.
A Note on Velocity Spectra in the Marine Boundary Layer 总被引:1,自引:1,他引:0
Spectra of longitudinal and vertical velocity have been studied at a marine site, östergarnsholm, in the Baltic Sea during a period of six days with near-neutral or slightly unstable conditions, when the wave state gradually changed from pure wind sea to strong swell having approximately the same direction as the wind. During the pure wind sea phase, spectra are shown to adhere closely to general forms for the neutral atmospheric surface layer obtained from a new theory. As soon as the wave age goes slightly beyond that representative of pure wind sea conditions, the spectra deviate in shape from the ideal forms. The spectral modification appears to start at a frequency typical of the swell component. As the wave age increases, it progresses in frequency as a downscale cascade, which is particularly prominent in the spectrum of the vertical component but which is also observed in the longitudinal component. In addition, there is a strong effect in the low-frequency part of the spectra. It is interpreted as an indirect effect of large-scale inactive turbulence, which becomes progressively more important as wave-age increases. It is found that the ratio of the spectrum of the vertical component and the spectrum of the corresponding longitudinal component attains the theoretically predicted value of 4/3 for cases of developing sea (gale force wind) for frequencies above approximately 4 Hz but never much exceeds unity for cases with swell. It is argued that this is an indication of local anisotropy and that the inertial-dissipation method for determination of the momentum flux is inappropriate in the case of mixed seas or swell. 相似文献
997.
Michail N. Taran Monika Koch-Müller Klaus Langer 《Physics and Chemistry of Minerals》2005,32(3):175-188
Natural Fe2+, Fe3+-bearing spinel solid solutions from the spinel s.s.-hercynite and gahnite-hercynite series were analyzed and studied by electronic absorption spectroscopy in the spectral range 30000–3500 cm–1 in the temperature and pressure ranges 77 TK 600 and 10–4 PGPa 11.0. Two crystals were light-violet in color (type I) and six green or bluish-green (type II). The spectra of both types of spinels are dominated by an UV-absorption edge near 28000 to 24000 cm–1, depending on the iron contents, and a very intense band system in the NIR centered around 5000 cm–1, which is caused by spin-allowed dd-transition of tetrahedral Fe2+, derived from 5 E5 T2. The strong band is in all spinels studied, split into four sub-bands, which can only be observed in very thin platelets. Between the UV-edge and the high-energy wing of the NIR-band there occur a number of very weak bands in type I spinels while the green type II spinels show some of these with significantly enhanced intensity. The intensity of the very weak bands is nearly independent from temperature. Such bands are attributed to spin-forbidden electronic transitions of IVFe2+. Temperature and pressure dependence of the intensity enhanced bands of spinels type II indicate that they are caused by IVFe2+ and VIFe3+. They are attributed to spin-forbidden transitions 6A1g4A1g, 4Eg, 4T2g and 4T1g of VIFe3+, the two latter being strongly intensified by exchange-coupling interaction with adjacent IVFe2+. The pressure dependence of IVFe2+ dd-band system in the NIR caused by spin-allowed 5 E5 T2 transition noticeably differs from that of octahedral Fe2+, an effect which is attributed to a dynamic Jahn-Teller effect of IVFe2+ in the spinel structure.
相似文献
Monika Koch-MüllerEmail: Phone: +49-331-288-1492/1402Fax: +49-331-288-1492/1402 |
998.
Y.?ZaslavskyEmail author A.?Shapira M.?Gorstein M.?Kalmanovich V.?Giller N.?Perelman I.?Livshits D.?Giller I.?Dan 《Bulletin of Earthquake Engineering》2005,3(3):355-381
Throughout their long history, the towns of Lod and Ramle have been severely affected by strong earthquakes. The last destructive
earthquake occurred on July 11, 1927 and caused the destruction of large parts of these cities, reaching a seismic intensity
of VIII–IX on the MSK scale. Such a high intensity from a relatively distant earthquake (about 70 km) of magnitude 6.2 is
likely to be the result of local site effects of the sedimentary layers that may have significantly enhanced earthquake ground
motions.
This study is focused on estimating the seismic hazard to Lod and Ramle by implementing a three-step process (1) detailed
mapping of the characteristics of the H/V spectral ratios from ambient noise, (2) incorporating geological information and well data to construct subsurface models
for different sites within the investigated area and (3) estimating the seismic hazard in terms of uniform hazard site-specific
accelerations.
The horizontal-to-vertical spectral ratios of ambient noise were used to approximate the fundamental resonance frequencies
of the subsurface and their associated amplitudes. About 360 sites in Lod and Ramle were instrumented for varying periods.
The soil sites exhibits H/V peak amplitudes ranging from 4 to 6 in the frequency range 0.5–2.5 Hz. These data were used to constrain 1-D subsurface models
that were developed using geological data and borehole information. H/V spectral ratio observations were checked against theoretical subsurface transfer functions at locations where borehole information
is available farther constraint the range of possible Vs velocities of the different layers and thus, by means of trial an error it was possible to conclude a systematic spatial
distribution of the Vs velocity and thickness in the substrata that are also consistent with the spatial distribution of the fundamental resonance
frequencies of the soft sediments obtained by means of the H/V spectral ratios, and other geological and geophysical information available at different locations in the study area.
The evaluated subsurface models are introduced using the SEEH procedure of Shapira and van~Eck [(1993) Natural Hazards 8, 201–205] to assess Uniform Hazard Site-Specific Acceleration Spectra for different zones within the towns of Lod and Ramle.
These evaluations are very important for realistic assessment of the vulnerabilities of all types of existing and newly designed
structures and for urban and land use planning. 相似文献
999.
Ahmed Badawy 《Journal of Seismology》2000,4(1):49-58
On 29–30 September 1996, an earthquake sequence occurred in the Füzesgyarmat region in eastern Hungary. The main shock had a magnitude of ML = 3.2 and was felt with a maximum intensity 4 MSK. It was preceded by a foreshock with a magnitude of ML = 2.8 and was followed, within six hours, by five aftershocks with magnitudes 2.1ML 3.1. The dynamic source parameters of the Füzesgyarmat earthquake sequence have been derived from P-wave spectra of the Hungarian seismograph stations. The average of the obtained values at different stations shows that the main shock occurred on a fault length of 610 m, with relative displacement of 1.13 cm, stress drop of 7 bar and seismic moment of 3.96*1021 dyne.cm. The main shock was small to yield data for a full mechanism solution and no reliable single fault plane solution could be obtained due to the low signal to noise ratio at the recording stations. The parameters of the foreshock are fault length of 560m, seismic moment of 2.09*1021 dyne.cm, stress drop of 5.53 bar and relative displacement of 0.73 cm. The five aftershocks show source parameters similar to the foreshock stress drops (5.26 5.76 bar), fault lengths (415 L 600 m), seismic moments (8.36*1020 Mo 2.31*1021 dyne.cm) and relative displacements (0.52 0.91 cm). 相似文献
1000.
含Mg矿物和玻璃中Mg的局部结构研究 总被引:2,自引:1,他引:1
本文用同步辐射的MgK-边X射线近边结构谱(XANES)研究了9种含Mg矿物的MgK-边特征谱,其谱的能量位置随着配位数的增加而增大;建立了含Mg矿物中Mgk-边的能量与Mg-O键距的关系CaMgSi2O6(Di)-NaAlSi3O8(Ab)玻璃中MgK-边XANES的能量和Mg-O的键长的关系.在Di-Ab玻璃中的Mg-O键距是0.2±0.004nm.表明本方法可以作为研究含Mg矿物Mg的配位与局部结构新的结构探针. 相似文献