The nature and origin of sideritic ironstone bands in the Tertiary Lowmead and Duaringa Basins,Queensland

Sideritic ironstones in Tertiary lacustrine oil shale from the Lowmead and Duaringa Basins in Queensland, contain two distinctive types of siderite in the ironstone bands: sphaerosiderite in the mudstone and coal, and finely crystalline siderite in the lamosite. The petrological evidence indicates that the siderite in the ironstone bands formed eogenetically by growing displacively within the soft sediment. Chemically the siderite is very pure though the sphaerosiderite sometimes shows compositional zoning. Stable oxygen and carbon isotope analyses of the siderite show a wide range of values from ‐12.8‰ to ‐2.4 %₀ δ¹⁸O (PDB) and ‐5.5‰ to +12.9‰ δ¹³C (PDB) for the Lowmead Basin; and ‐9.6‰ to ‐1.2‰ δ¹⁸O (PDB) and ‐18.6‰ to +16.4‰ δ¹³C (PDB) for the Duaringa Basin. The oxygen isotope data indicate that the siderite formed in freshwater environments but not in isotopic equilibrium with the formation waters. Kinetic factors offer the most plausible explanation for the anomalously light δ¹⁸O values of many of the siderites. The carbon isotope data show that the carbonate for the formation of the siderite originated predominantly from methanogenic fermentation processes but there was also the varying influence of bacterial oxidation processes. The different petrological and isotopic characteristics of the ironstones broadly reflect variations in their depositional environments and the variable eogenetic conditions in which the siderite formed. There is no suitable single model to explain the genesis of all the different types of ironstones other than that a synsedimentary iron‐enrichment process is involved.     

An elliptical basis function network for classification of remote sensing images

An elliptical basis function (EBF) network is employed in this study for the classification of remotely sensed images. Though similar in structure, the EBF network differs from the well-known radial basis function (RBF) network by incorporating full covariance matrices and employing the expectation-maximization (EM) algorithm to estimate the basis functions. Since remotely sensed data often take on mixture-density distributions in the feature space, the network not only possesses the advantage of the RBF mechanism, but also utilizes the EM algorithm to compute the maximum likelihood estimates of the mean vectors and covariance matrices of a Gaussian mixture distribution in the training phase. Experimental results show that the EM-based EBF network is more effective in training and simpler in structure than an RBF network constructed for the same task.The research was supported by grant 40101021 from the Natural Science Foundation of China, and grant 2002AA135230 from Hi-Tech research and development program of China. The authors would like to thank the reviewers for their valuable comments.     

孔隙溶液对粉质黏土界限含水率的影响

针对桂林地区的粉质黏土,运用液、塑限联合测定法探讨了不同孔隙溶液作用下土体的界限含水率,并利用扫描电镜（SEM）技术从微观层面分析了水化学环境变异下土体的水化学-力学耦合作用对结构特性造成的影响。试验结果表明,随着孔隙溶液浓度的增大,粉质黏土的界限含水率均减小,且在相同浓度下同价阳离子半径较小的水溶液使得粉质黏土界限含水率下降的较为明显,随着阳离子价位的增高,其下降的幅度更大;该现象的产生主要是由于离子浓度及离子价位的增大,使得扩散双电层的厚度减小,而双电层对于土体界限含水率存在直接的控制作用。除此以外,通过探测土体的微观结构发现,水化学-力学耦合作用使得粉质黏土颗粒间发生絮凝作用,致使土粒形成粒团,土颗粒间孔隙增大,架空孔隙变多。     

用经验正交函数构造武汉地区电子浓度总含量的经验模式

本文利用经验正交函数（Empirical Orthogonal Function, 简称EOF）分析了武汉电离层台站一个太阳黑子周期（1980年4月～1990年12月）的实测电离层电子浓度总含量（TEC）资料,在此基础上构建了一个武汉地区的TEC月中值的经验模式.结果表明：（1）以EOF分析观测数据具有一定的物理意义,其基函数表征TEC的日变化,系数表征TEC的长期变化;（2）EOF技术展开收敛速度快,很少数低阶项即能反映TEC的主要变化,采用经验正交函数建模可以用较少的参数表征较复杂的物理过程.此外,本文还就TEC模式的外部驱动量的改进问题作了一些探讨,发现用F107A（10.7cm太阳辐射通量F107的81天滑动平均值）作TEC建模的外部驱动量能够更好地提高EOF模式的精度和稳定性.     

高频多普勒台阵中的若干技术问题

为了研究电离层动力学特性,1985年9月在武汉建成了一个由三个台站组成的高频多普勒台阵和卫星信标法拉第台阵。文中介绍了这个台阵的布局和多普勒接收系统中的一些技术细节。这些技术措施保证了在多普勒图中清晰地显示多径现象和有效地消除小不均匀体的影响。最后还简单地介绍了这个台阵一年来的实测情况。     

Using VLBI fringe-phase information from geodetic experiments for short-period ionospheric studies

The usage of Very Long Baseline Interferometry (VLBI) fringe-phase information in geodetic VLBI is a new field of research, which can be used for the detection of short-period (i.e., several minutes) variations (scintillations) of the ionosphere. This paper presents a method for the extraction of such disturbances and discusses how dispersive influences can be separated from intra-scan delay variations. A proper functional and stochastic model for the separation of the different effects is presented and the algorithms are applied to real measurements. In an example, it is shown that a traveling ionospheric disturbance in Antarctica can be detected very precisely. A possible physical origin and the propagation properties of the disturbance are presented and the results are compared with GPS measurements. The benefit of this method for other applications is also discussed.     

Monazite age spectra in the Late Cenozoic strata of the Changjiang delta and its implication on the Changjiang run-through time

Uplift of the Tibetan Plateau, inversion of eastern and western geomorphology, eastward flowing of large rivers, and run-through of the Changjiang River exert great influence on sedimentation and environ-mental variations in the East China Sea. Provenance discrimination of Tibetan-Plateau-originated sediments in the river-mouth areas and marginal seas is key to figure out these issues.In the past, most studies of the run-through time of the Changjiang and the Yellow rivers focused on geomo…     

土壤中14过渡矿物的特征及其地质意义

14过渡矿物是广泛发育的典型成土作用产物,其矿物学特征及含量变化不仅能记录成土时期的气候、环境条件,也可以作为这些土壤发生分类和类型区分的依据。通过对有关14过渡矿物研究成果系统全面的分析,阐明了这种过渡矿物的谱学特征、层间离子类型、鉴定依据及其成因,并在此基础上提出对14过渡矿物的鉴定实验流程。此外,高分辨透射电子显微技术的应用给14过渡矿物的研究提供了极大的保障,利用高分辨透射电子显微镜可以研究14过渡矿物的形成、转化关系。14过渡矿物对气候环境十分敏感,且形成于特征的干湿交替、适度的风化及弱酸性环境条件,因此,这种过渡矿物有望作为成土时期的气候环境代用指标。     

Low density ionized gas in the inner galaxy — Interpretation of recombination line observations at 325 MHz

The recent survey of H 272α recombination line (324.99 MHz) in the direction of 34 Hn regions, 12 SNRs and 6 regions of continuum minimum (‘blank’ regions) in the galactic plane is used to derive the properties of diffuse ionized gas in the inner Galaxy. The intensity of radio recombination lines at high frequencies is dominated by spontaneous emission in high-density gas and that at low frequencies (325 MHz) by stimulated emission in low-density gas. We have used this property to obtain the electron density in the gas in the direction of blank regions and SNRs, by combining the H 272 α measurements (preceeding paper) with the published data at higher frequencies. Further, we have imposed constraints on the electron temperature and pathlength through this gas using the observed high-frequency continuum emission, average interstellar electron density and geometry of the line-emitting regions. The derived properties of the gas are (i) electron density 0.5–6 cm^-3, (ii) electron temperature 3000–8000 K and (iii) emission measures 500–3000 pc cm^-6 The corresponding pathlengths are 50–200 pc. As the derived sizes of the low-density regions are small compared to the pathlength through the Galaxy, the low-frequency recombination lines cannot be considered as coming from a widely distributed component of the interstellar medium. The Hn regions studied in the above survey cannot themselves produce the H 272α lines detected towards them because of pressure broadening, optical depth, and beam dilution. However, the agreement in velocity of these lines with those seen at higher frequencies suggests that the low-frequency recombination lines arise in low-density envelopes of the Hn regions. Assuming that the temperature of the envelopes are similar to those of the cores and invoking geometrical considerations we find that these envelopes should have electron densities in the range 1–10 cm^-3 and linear sizes of 30–300 pc in order to produce the observed H 272α lines.     

养殖锯缘青蟹呼肠孤样病毒粒子的电镜观察

经过对患病青蟹Scylla serrata的组织进行了超薄切片电镜观察,在病蟹的鳃上皮细胞、心肌细胞、胃和肠道上皮细胞中发现了大量的呼肠孤样病毒粒子。该病毒粒子的大小为60 nm左右,二十面体对称,无囊膜,在感染组织细胞浆中呈晶格状排列。根据病毒的形态特征和组织分布形态,初步认为该病毒为水生呼肠孤病毒,暂将其命名为青蟹呼肠孤病毒(Scylla serratareo-like virus,Ss-REO)。