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81.
The spatial distribution of snow cover on the central Arctic sea ice is investigated here based on the observations made during the Third Chinese Arctic Expedition. Six types of snow were observed during the expedition: new/recent snow, melt-freeze crust, icy layer, depth hoar, coarse-grained, and chains of depth hoar. Across most measurement areas, the snow surface was covered by a melt-freeze crust 2-3 cm thick, which was produced by alternate strong solar radiation and the sharp temperature decrease over the summer Arctic Ocean. There was an intermittent layer of snow and ice at the base of the snow pack. The mean bulk density of the snow was 304.01±29.00 kg/m3 along the expedition line, and the surface values were generally smaller than those of the subsurface, confirming the principle of snow densification. In addition, the thicknesses and water equivalents of the new/recent and total-layer snow showed a decreasing trend with latitude, suggesting that the amount of snow cover and its spatial variations were mainly determined by precipitation. Snow temperature also presented significant variations in the vertical profile, and ablation and evaporation were not the primary factors in the snow assessment in late summer. The mean temperature of the surface snow was 2.01±0.96°C, which was much higher than that observed in theinterface of snow and sea ice. 相似文献
82.
Abstract This work makes explicit an algebraic expression giving the matrix of transient influence coefficients associated with a one-dimensional semi-confined aquifer model. The domain studied is divided into a series of connected and completely mixed compartments over which the governing equation is discretized. The discrete equations obtained are solved for the compartmental hydraulic head and used to derive the algebraic expression in question. The basic properties of the so-called algebraic influence coefficients are investigated. In particular, their consistency with the exact Green function is highlighted. Finally, the newly derived influence coefficients are applied to a simplified aquifer system in order to formulate and solve the problem of identifying illegal groundwater pumping. 相似文献
83.
84.
Single-crystal electron paramagnetic resonance (EPR) spectra of fast-electron-irradiated quartz, after annealing at 120 and
200°C, reveal five new E′ type centers, herein labeled
E 5¢ , E 6¢ , E 7¢ , E 8¢ , \textand E 9¢ E_{ 5}^{\prime } ,\,E_{ 6}^{\prime } ,\,E_{ 7}^{\prime } ,\,E_{ 8}^{\prime } ,\,{\text{and}}\,E_{ 9}^{\prime } . Centers
E 5¢ , E 7¢ , \textand E 9¢ E_{ 5}^{\prime } ,\,E_{ 7}^{\prime } ,\,{\text{and}}\,E_{ 9}^{\prime } are characterized by the orientations of the unique principal g and A(29Si) axes close to a short Si–O bond direction, hence representing new variants of the well-established E 1¢ E_{ 1}^{\prime } center. Centers E 6¢ E_{ 6}^{\prime } and E 8¢ E_{ 8}^{\prime } have the orientations of the unique principal g and A(29Si) axes approximately along a long Si–O bond direction, similar to the E 2¢ E_{ 2}^{\prime } centers. Therefore, these new E′ type centers apparently arise from the removal of different oxygen atoms and represent variable local distortions around
the oxygen vacancies. 相似文献
85.
Borates consisting of diverse fundamental building blocks (FBB) formed from complex polymerization of planar triangular [Bϕ3] groups and tetrahedral [Bϕ4] groups, where ϕ = O and OH, provide an excellent opportunity for investigation of correlations between the NMR parameters
and local structures. However, previous studies suggested that the 11B NMR parameters in borates are insensitive to local structural environments other than the B coordination number, in contrast
to those documented for 29Si, 23Na and 27Al in silicates, and no correlation between 11B chemical shifts and the sum of bond valences has been established for borate minerals with hydroxyl groups or molecular
water in the structures. In this study, high-resolution NMR spectra have been acquired at the ultra high field of 21 T as
well as at 14 T for selected borate and borosilicate minerals, and have been used to extract high-precision NMR parameters
by using combined ab initio theoretical calculations and spectral simulations. These new NMR parameters reveal subtle correlations
with various structural characters, especially the effects of the 11B chemical shifts from the bridging oxygen atom(s), site symmetry, symmetry of FBB, the sum of bond valences, as well as the
next-nearest-neighbor cations and hydrogen bonding. Also, these results provide new insights into the shielding mechanism
for 11B in borate and borosilicate minerals. In particular, this study demonstrates that the small variation in 11B chemical shifts can still be used to probe the local structural environments and that the established correlations can be
used to investigate the structural details in borates and amorphous materials. 相似文献
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89.
Hydrogeochemical and isotopic study of groundwater in the Habor Lake Basin of the Ordos Plateau,NW China 总被引:2,自引:2,他引:0
Lihe Yin Guangcai Hou Yan Dou Zhengping Tao Ying Li 《Environmental Earth Sciences》2011,64(6):1575-1584
Hydrogeochemistry and isotopes were used to understand the origin and geochemical evolution in the Habor Lake Basin, northwestern
China. Groundwater samples were taken, and the isotopic compositions δD, δ18O and major ions were analyzed. The groundwater can be divided into three types: the Quaternary groundwater, the shallow Cretaceous
groundwater and the deep Cretaceous groundwater. The groundwater chemistry is mainly controlled by the feldspar weathering
and dolomite weathering, the dissolution of Glauber’s salt, and cation exchange. Chemistry of lake water is mainly controlled
by evaporation and precipitation. The stable isotopes of oxygen and hydrogen in groundwater cluster along the local meteoric
water line, indicating that groundwater is of meteoric origin. Comparing with shallow groundwater, deep groundwater is depleted
in heavy isotopes indicating that deep groundwater was recharged during late Pleistocene and Holocene, during which the climate
was more wetter and colder than today. 相似文献
90.
根据2009年2月对三门湾海域的环境质量调查结果,结合海洋环境功能区划对该海域环境质量现状进行了评价与分析;并综合分析了水质中富营养化程度,沉积物中重金属的富集程度及潜在生态危害效应。结果表明:该海域水质除无机氮和Hg外其他环境因子基本符合功能区相应的海水水质标准,水质状况尚好。61.5%站位的富营养化指数大于1,表明该海区富营养化程度较高;该海域沉积物除少数站位的Cu、Cr外,其他环境因子的含量均达标,底质环境状况良好。各站位潜在生态危害系数均远小于150,说明三门湾海域沉积物中重金属的潜在生态危害属于轻微危害范围。 相似文献