Influence of neutral transport on ion chemistry uncertainties in Titan ionosphere     

N. Carrasco  E. Hbrard  M. Banaszkiewicz  M. Dobrijevic  P. Pernot 《Icarus》2007,192(2):519-526

Models of Titan ionospheric chemistry have shown that ion densities depend strongly on the neutral composition. The turbulent diffusion transport conditions, as modeled by eddy coefficients, can spectacularly affect the uncertainty on predicted neutral densities. In order to evaluate the error budget on ion densities predicted by photochemical models, we perform uncertainty propagation of neutral densities by Monte Carlo sampling and assess their sensitivity to two turbulent diffusion profiles, corresponding to the extreme profiles at high altitudes described in the literature. A strong sensitivity of the ion density uncertainties to transport is observed, generally more important than to ion–molecule reaction parameters themselves. This highlights the necessity to constrain eddy diffusion profiles for Titan ionosphere, which should progressively be done thanks to the present and future measurements of the orbiter Cassini.  相似文献   

Ionic composition and mineral equilibria of acidic groundwater on the west coast of Sweden     

J. Sjöström 《Environmental Geology》1993,21(4):219-226

The groundwater chemistry of 14 shallow wells and 10 springs in Halland, southwest Sweden, and precipitation have been studied in trilinear diagrams. Ionic strength and saturation index (SI) for selected minerals have been calculated. Five springwaters have similar chemical composition to that of the precipitation, which indicates surficial and rapidly recharged water. The SI of the groundwaters is out of equilibrium (undersaturated) with respect to primary silicates such as mafic minerals, feldspar, K-mica and chlorite, but in equilibrium with solid SiO₂ (quartz, cristobalite, or chalcedony). The SI shows oversaturation conditions for kaolinite, hydroxy-Al interlayered vermiculite, Na,K,Mg-beidellite, Mg-montmorillonite, and AB-montmorillonite. Concentrations of soluble Al and Si can be governed by Mg,Fe-beidellite, BF-montmorillonite, or Ca-montmorillonite at four springs, and by halloysite at two wells on the coastal plain. For these groundwaters, clay minerals may act as H⁺ buffers and thus have an influence on pH and toxic Al, i.e., parameters affecting the drinking water quality and environment. The study shows that the soil catena are intensily weathered at the investigated sites. It is further concluded that neither cation exchange nor primary silicate weathering will keep up with buffering the acidic loads into the soils. A general prediction of groundwater quality is presented.  相似文献   

泗顶—古丹铅锌矿田铅同位素组成特征及其地质意义     

张术根 《南方国土资源》1989,(4)

笔者根据泗顶—古丹铅锌矿田矿石铅同位素组成特征,并结合矿田成矿地质背景,探讨其地质意义。研究结果表明:方铅矿的铅同位素组成特征随硫同位素组成特征和矿化场所的变化而变化,铅同位素组成模式年龄依矿田出现的地质事件可分两组(410—600Ma,180—260Ma),并可建立起二源线性混合方程,因此,成矿物质来源具两源性。故认为泗顶——古丹铝锌矿田的硫化物矿床,成矿物质来源于加里东运动褶皱基底轻微变质的寒武系和盖层泥盆系,含矿溶液是赋存于该两个地层中的地下水混合产物,即二源地下水混合成矿作用结果。  相似文献   

The effect of refreezing on the isotopic composition of melting snowpack     

Shiqiao Zhou  Masayoshi Nakawo  Shigemasa Hashimoto  Akiko Sakai 《水文研究》2008,22(6):873-882

The isotopic composition of solid and liquid portions of natural melting snowpack is investigated in detail by the separating of liquid water from snow grains at different depths of the snowpack. The slope of the δD–δ¹⁸O line for the liquid phase is found to be lower than for the solid phase. This is proved to be due to the isotopic fractionation occurring in the melt–freeze mass exchange within the snowpack. Melting of the snowpack has no clear impact on the δD–δ¹⁸O line for the solid phase, but the slope of the δD–δ¹⁸O line for the liquid shows an overall slight decrease in the melting period. When the snowpack is refrozen, the refreezing process would inevitably cause the slope of the solid phase to decrease because of the discrepancy between the slopes of the two phases. Thus the slope of the solid would become lower and lower as the diurnal melt–freeze episodes cycle throughout the melting season. This effect is then demonstrated by looking into the isotopic composition changes of glacier firn. The extent of the effect depends on the snowpack properties and environmental conditions. The slope changes also result in a decreasing trend in deuterium excess. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Cokriging of regionalized compositions     

V. Pawlowsky 《Mathematical Geology》1989,21(5):513-521

To avoid spurious spatial correlation when analyzing the spatial covariance structure of regionalized compositions, additive-log-ratio transformation can be used. Here, the additive-log-ratio cokriging estimator, derived in a natural way from this transformation, is shown to be invariant under permutation of components of the untransformed regionalized composition. It leads, as expected, to an exact interpolation. As original data, predicted values of the regionalized composition at unknown points add up to the same constant c and lie between 0 and c.  相似文献   

Comment on “Methane on Mars: A product of H₂O photolysis in the presence of CO” by A. Bar-Nun and V. Dimitrov     

Vladimir A. Krasnopolsky 《Icarus》2007,188(2):540-542

Bar-Nun and Dimitrov [Bar-Nun, A., Dimitrov, V., 2006. Icarus 181, 320-322] suggested a sequence of reactions to form methane on Mars. These reactions are based on the study of products in the N₂-CO-H₂O mixture irradiated at 185 nm. The suggested scheme was not quantitatively justified by chemical kinetics. One of the key reactions is effectively blocked by O₂ in the martian atmosphere, and another key reaction does not exist. There are no pathways for effective formation of methane in the martian atmosphere.  相似文献   

Ion chemistry and N-containing molecules in Titan's upper atmosphere     

V. Vuitton  R.V. Yelle 《Icarus》2007,191(2):722-742

High-energy photons, electrons, and ions initiate ion-neutral chemistry in Titan's upper atmosphere by ionizing the major neutral species (nitrogen and methane). The Ion and Neutral Mass Spectrometer (INMS) onboard the Cassini spacecraft performed the first composition measurements of Titan's ionosphere. INMS revealed that Titan has the most compositionally complex ionosphere in the Solar System, with roughly 50 ions at or above the detection threshold. Modeling of the ionospheric composition constrains the density of minor neutral constituents, most of which cannot be measured with any other technique. The species identified with this approach include the most complex molecules identified so far on Titan. This confirms the long-thought idea that a very rich chemistry is actually taking place in this atmosphere. However, it appears that much of the interesting chemistry occurs in the upper atmosphere rather than at lower altitudes. The species observed by INMS are probably the first intermediates in the formation of even larger molecules. As a consequence, they affect the composition of the bulk atmosphere, the composition and optical properties of the aerosols and the flux of condensable material to the surface. In this paper, we discuss the production and loss reactions for the ions and how this affects the neutral densities. We compare our results to neutral densities measured in the stratosphere by other instruments, to production yields obtained in laboratory experiments simulating Titan's chemistry and to predictions of photochemical models. We suggest neutral formation mechanisms and highlight needs for new experimental and theoretical data.  相似文献   

柴达木盆地西北部红三旱地区始新世-渐新世砂岩物源分析   总被引：3，自引：1，他引：3  

刘欢刘永江  袁四化计桂霞 李伟民 《地质通报》2007,26(1):100-107

柴达木盆地西部红三旱一号三高点上、下干柴沟组砂岩的骨架矿物成分的模式分析显示,始新统—渐新统砂岩的源区主要为再旋回造山带。根据古水流推断物源区主要为阿尔金山。结合上、下干柴沟组砂岩成分模式分析的标准偏差对比和骨架矿物成分平均含量的变化特征,认为渐新世时(上干柴沟组)阿尔金山存在一期隆升事件。  相似文献   

金宝山铂钯矿矿石的矿物成分及嵌布特征     

宋焕斌  张尚忠  易凤煌 《矿产与地质》2007,21(1):22-26

金宝山铂钯矿属于中国最大的独立铂族金属矿床,铂钯矿石的成分十分复杂,已发现73种矿物,其中有贵金属矿物25种、铂族矿物21种。矿石结构复杂,铂族金属矿物粒度很细,主要为10~80μm,其中20~40μm者占58.18%。贵金属矿物主要分布在蛇纹石中,占46.67%,有25.03%的贵金属矿物分布在黄铜矿中,其他载体矿物有镍硫化物、黄铁矿和磁铁矿等。矿石属于微细粒难选矿石。  相似文献   

赣中周潭群变质岩中石榴石的演化史及其地质意义     

胡恭任 《矿物岩石》2007,27(2):33-38

周潭群变质岩系中石榴石、十字石和黑云母微区化学成分变化明显,石榴石变斑晶具典型的生长环带,由晶体中心向两侧边缘XMg,XFe值递增,XCa,XMn值递减,反映增温过程,晶体最边缘的化学成分反映变质峰期的温度条件。变质岩系经历了角闪岩相变质作用,划分为3个变质阶段。各阶段石榴石的分布、形态、矿物组合、化学成分及其成因条件存在一定差异。通过成因矿物学的系统研究,确定本区变质岩系石榴石的结晶生长演化史及变晶变形序列。  相似文献