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排序方式: 共有315条查询结果,搜索用时 15 毫秒
91.
This paper summarises the development and principal results of fifty years of research on aerosols in the marine atmosphere at Mace Head Atmospheric Research Station on the west coast of Ireland. It concentrates on the sources, physico-chemical properties, number and mass concentrations, size range, volatility and chemical composition of aerosols in different air masses. It also examines optical properties of the aerosols and their long-range transport. 相似文献
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93.
Timothy J. Stubbs David A. Glenar Anthony Colaprete Denis T. Richard 《Planetary and Space Science》2010,58(5):830-1934
The Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft will orbit the Moon at an altitude of ≈50 km with a payload that includes the Ultraviolet Spectrometer (UVS) instrument, which will obtain high spectral resolution measurements at near-ultraviolet and visible wavelengths (≈231-826 nm). When LADEE/UVS observes the lunar limb from within the shadow of the Moon it is anticipated that it will detect a lunar horizon glow (LHG) due to sunlight scattered from submicron exospheric dust, as well as emission lines from exospheric gases (particularly sodium), in the presence of the bright coronal and zodiacal light (CZL) background. A modularized code has been developed at NMSU for simulations of scattered light sources as observed by orbiting instruments in lunar shadow. Predictions for the LADEE UVS and star tracker cameras indicate that LHG, sodium (Na) emission lines, and CZL can be distinguished based on spatial morphology and spectral characteristics, with LHG dominant at blue wavelengths (∼250-450 nm) and small tangent heights. If present, LHG should be readily detected by LADEE/UVS and distinguishable from other sources of optical scattering. Observations from UVS and the other instruments aboard LADEE will significantly advance our understanding of how the Moon interacts with the surrounding space environment; these new insights will be applicable to the many other airless bodies in the solar system. 相似文献
94.
Fifteen samples of (Mg,Fe)SiO3 majorite with varying Fe/Mg composition and one sample of (Mg,Fe)(Si,Al)O3 majorite were synthesized at high pressure and temperature under different conditions of oxygen fugacity using a multianvil press, and examined ex situ using X-ray diffraction and Mössbauer and optical absorption spectroscopy. The relative concentration of Fe3+ increases both with total iron content and increasing oxygen fugacity, but not with Al concentration. Optical absorption spectra indicate the presence of Fe2+–Fe3+ charge transfer, where band intensity increases with increasing Fe3+ concentration. Mössbauer data were used in conjunction with electron microprobe analyses to determine the site distribution of all cations. Both Al and Fe3+ substitute on the octahedral site, and charge balance occurs through the removal of Si. The degree of Mg/Si ordering on the octahedral sites in (Mg,Fe)SiO3 majorite, which affects both the c/a ratio and the unit cell volume, is influenced by the thermal history of the sample. The Fe3+ concentration of (Mg,Fe)(Si,Al)O3 majorite in the mantle will reflect prevailing redox conditions, which are believed to be relatively reducing in the transition zone. Exchange of material across the transition boundary to (Mg,Fe) (Si,Al)O3 perovskite would then require a mechanism to oxidize sufficient iron to satisfy crystal-chemical requirements of the lower-mantle perovskite phase. 相似文献
95.
Geochemical characterization, correlation, and optical dating of tephra in alluvial sequences of central western Argentina 总被引:1,自引:0,他引:1
The synthesis of paleoclimatic archives provided by loess and alluvial sequences of central Argentina has been hindered by the lack of a cohesive lithostratigraphic framework extending across the Chaco-Pampean plains and catchments of the Rios Desaguadero, Colorado, and Negro. This condition originates in part from the dearth of absolute chronological controls. The occurrence of discrete tephra layers across this region may provide an opportunity to address this deficiency if a tephrochronological framework can be established. The potential of such a project is assessed within the context of a pilot study constrained within alluvial sequences of central western Argentina proximal to potential source vents in the Southern Volcanic Zone. The intersite discrimination and correlation of tephra layers on a geochemical basis is examined, with indirect chronological control for the eruption of each generated by optical dating. Alluvial sediments on either side of each of five tephra units at a type site were dated using the optically stimulated luminescence of fine-silt-sized quartz, thus providing an age control on each tephra (ca. 24,000, 30,000, 32,000, 39,000, and 48,000 yr). The geochemical composition of each tephra was derived. Using these data, tephra layers at other sites in the study area were geochemically analyzed and, in instances of statistical concordance in major oxide structure, correlated to the type site and therefore ascribed ages. This methodology identified a further sixth volcanic event between ca. 24,000 and 30,000 yr not registered by type-site tephras. The extension of this initial tephrochronological framework beyond the alluvial sequences of central western Argentina is encouraged by the occurrence of geochemically distinct tephra verified and dated in this study. 相似文献
96.
本文扼要介绍了PMOE行星历表研究当前的进展和工作 ,给出了PMOE2 0 0 2与DE40 5历表的比较。 相似文献
97.
V. P. Solntsev E. G. Tsvetkov A. I. Alimpiev R. I. Mashkovtsev 《Physics and Chemistry of Minerals》2006,33(5):300-313
We have studied the polarized optical absorption and the EPR spectra of Ni-doped beryls grown by hydrothermal, flux and gas-transport methods, and chrysoberyl grown by the Czochralski and flux methods. In beryls, three groups of bands belonging to three various Ni centres were distinguished by analysis of the absorption band intensities. The first group, bands with maximums at 21740 (E ⊥ c), 17240 (E || c) and 9260 (E ⊥ + || c), 7140 (E || + ⊥ c) cm−1, are due to Ni3+ in octahedral Al3+ site. The second group is bands at 25640 (E ⊥ c), 22220 (E || c) and 13520 (E || + ⊥ c), 13160 (E ⊥+ || c) cm−1 and 8930 (E ⊥ + || c), 7460 (E || c) cm−1, which are caused by Ni2+ in octahedral Al3+ site. Weak wide bands at 17540 (E ⊥ c), 15500 (E || c) cm−1 and 6580 (E || + ⊥ c), 5950 (E || c) cm−1 are related to Ni2+ in tetrahedral Be2+ site. The occurrence of Ni ions in Be2+ site is proved by the EPR spectra of 1VNi+ in γ-irradiated samples. According to the spectra of optical absorption of Ni-doped chrysoberyl, two types of Ni centres have been established: Ni3+ and Ni2+ ions in octahedral Al3+ sites. From the EPR spectra of the X-ray irradiated crystals BeAl2O4: Ni, it follows that 68% of Ni+ ions occupy octahedral Al3+ sites with mirror symmetry and 32% are in Al3+ sites with inversion symmetry. In the approximation of trigonal field with regard to Trees correction, the energy levels of Ni3+ and Ni2+ have been calculated in octahedral and tetrahedral coordination. There is good agreement between the obtained experimental and calculated data. The polarization dependence of the optical absorption bands is well explained in terms of the spin–orbit interaction. 相似文献
98.
99.
100.
Integrated Sensible Heat Flux Measurements of a Two-Surface Composite Landscape using Scintillometry 总被引:1,自引:0,他引:1
J.-P. Lagouarde J.-M. Bonnefond Y. H. Kerr K. J. McAneney M. Irvine 《Boundary-Layer Meteorology》2002,105(1):5-35
The potential of the LAS (large aperture scintillometry) method for measuring sensible heat flux (H) directly integrated over a two-field composite surface is evaluated. We describe a field experiment performed within the Alpilles/ReSeDa project in the south-east of France over a composite surface made up of wheat and bare soil (451 and 216 m long respectively) using two 0.15-m diameter scintillometers mounted at heights of 2.05 and 4.54 m. When compared against reference values obtained by the eddy correlation technique, LAS-measured sensible heat flux reveals a systematic overestimation of about 10%. A simple model describing the integration of the scintillometer signal along the beam for a two-field composite surface is described. A simulation of the experiment confirms that the bias observed isrelated to non-linearities in the integration process in relation with thebell-shape sensitivity curve of the instrument to the structure parameter for the refractive index it measures. The model is used to test the sensitivity of the LAS-derived H values to the composition of the pathlength (ratio of both surfaces) and to the contrast in sensible heat flux and roughness length between the two fields. Sensitivity tests to the aggregation scheme for roughness length (two of them are tested) and to the measurement height are also presented. The composition of the surface in combination with the contrast in sensible heat flux (in direct relation with the contrast in latent heat flux) explains most of the bias, with possible deviations ranging from -50 up to 80 W m-2. A tentative semi-empirical method for correcting the bias is suggested, which only requires a crude estimate of the contrast in component sensible heat fluxes along the pathlength. 相似文献