Heat capacity of γ-Fe2SiO4 between 5 and 303 K and derived thermodynamic properties

A multi-anvil device was used to synthesize 24 mg of pure γ-Fe₂SiO₄ crystals at 8.5 GPa and 1,273 K. The low-temperature heat capacity (C _p) of γ-Fe₂SiO₄ was measured between 5 and 303 K using the heat capacity option of a physical properties measurement system. The measured heat capacity data show a broad λ-transition at 11.8 K. The difference in the C _p between fayalite and γ-Fe₂SiO₄ is reduced as the temperature increases in the range of 50–300 K. The gap in C _p data between 300 and 350 K of γ-Fe₂SiO₄ is an impediment to calculation of a precise C _p equation above 298 K that can be used for phase equilibrium calculations at high temperatures and high pressures. The C _p and entropy of γ-Fe₂SiO₄ at standard temperature and pressure (S°₂₉₈) are 131.1 ± 0.6 and 140.2 ± 0.4 J mol⁻¹ K⁻¹, respectively. The Gibbs free energy at standard pressure and temperature (ΔG° _f,298) is calculated to be −1,369.3 ± 2.7 J mol⁻¹ based on the new entropy data. The phase boundary for the fayalite–γ-Fe₂SiO₄ transition at 298 K based on current thermodynamic data is located at 2.4 ± 0.6 GPa with a slope of 25.4 bars/K, consistent with extrapolated results of previous experimental studies.     

The Cretaceous System in China

This paper provides an outline of Cretaceous stratigraphy and paleogeography in China, which is based on rich data obtained from recent researches. Cretaceous deposits are widespread in China. Most strata are of nonmarine origin and marine sediments occur only in Tibet, western Tarim Basin of Xinjiang, Taiwan and limited localities of eastern Heilongjiang. All deposits are rich in fossils and well-constrained biostratigraphically. The stratigraphic successions of different regions are illustrated, and general stratigraphic division and correlation have been introduced. The marine deposits are described in the Tibetan Tethys, Kashi-Hotan Region of Xinjiang, eastern Heilongjiang, western Yunnan and Taiwan; the nonmarine deposits are outlined from northeast China, southeast China, southern interior China, southwest China, the Shaanxi-Gansu-Ningxia region, and northwestern China intermontane basins. The sedimentary facies and paleogeography are diversified. In Tibet the basin evolution is largely related to the subduction and collision of the Indian Plate against the Eurasian Continent, and shows a tectonic evolution in the Cretaceous. Foraminifera are a dominant biota in the Tibet Tethys. Nonmarine sediments include variegated and red beds, coal- or salt-bearing horizons, and volcanic rocks. These deposits contain diverse and abundant continental faunas and floras, as well as important coal and oil resources. The Cretaceous stratigraphy and paleogeography in China have presented a foundation for geological studies.     

坝基集中渗漏通道的温度场反分析与试验研究

渗漏是严重影响堤坝安全的主要形式,确定渗漏通道的位置是进行堤坝渗漏整治的前提和基础。温度场探测堤坝渗漏的研究是其中一种较便捷的方法,但是在理论上还需要进一步完善。在库水和地下水存在着温度差异的基础上,考虑堤坝发生集中渗漏后,渗漏通道中的地下水与周围土体进行热量交换,造成渗流通道附近地层温度发生改变,建立起温度场对渗漏通道的反演模型。在前人研究的基础上,考虑地温梯度的影响,可以建立有集中渗漏通道影响下的二维热传导方程,进而以现场测井的温度数据作为边界条件,对泛定方程进行求解,最终得到渗漏通道的位置。计算结果和实测结果的对比表明,通过温度场反推渗漏通道参数的方法是可行的。     

制度约束与路径选择——珠三角高密集城中村治理改造的困境与出路

从珠三角高密集城中村的形成入手，探讨其与外向型乡村城市化以及相关制度约束的关系，从而揭示了高密集城中村空间现象的形成过程。同时，对近年来珠三角各城市治理与改造高密集城中村的相关模式与对策进行梳理与评价，指出目前珠三角各城市的城中村治理中的挫折与困境（适应性效率不足），客观上反映了国家宏观制度供给结构与先行快速城市化地区的制度落差，珠三角大都市地区城中村的最终都市化将是一个长期的过程。文中针对目前城中村治理改造的问题与困境，提出珠三角高密集城中村空间治理予以重视的若干政策思路。     

重大项目对区域经济空间的影响——以广州市钟村镇新火车客站建设为例

在区域经济发展过程中,重大项目的影响比一般的经济因素显得更为重要和关键。而对受影响的区域来说,在我国现行行政区划体制下,乡镇所受的影响更为直接。2003年,广州新火车客站(以下简称新客站)规划选址于钟村镇石壁地区,引起了国内外的极大关注。通过实证分析,发现新客站的建设将会引起当地经济空间结构的极大改变,同时也会带来一系列的社会问题。     

沙拐枣属（Calligonum L.）7种植物总DNA提取方法的改进及鉴定

 摸索沙拐枣属（Calligonum L.）七种植物沙拐枣（Calligonum mongolicum Turcz. ）、泡果沙拐枣（C. junceum (Fisch. et Mey.) Endl.）、无叶沙拐枣（C. aphyllum (Pall.) Gürke）、红果沙拐枣（C. rubicundum Bge.）、心形沙拐枣（C. cordatum E. Kor. ex N. Pavl.）、密刺沙拐枣(C. densum Borszcz.)、乔木状沙拐枣（C. arborescens Litv.）的总DNA提取方法并对DNA样品的纯度和浓度进行鉴定,对传统的CTAB法进行方法和材料的改进,开展与总DNA相关的PCR扩增和其他遗传学分析,并取得满意的结果。其结果对于沙拐枣属植物的有关研究提供了有效的实验手段。     

NUMERICAL STUDY ON THE MIXING OF UNSORTED SEDIMENT PARTICLES DISCHARGED INTO A CROSS-FLOW BY MULTIPHASE PARTICLE-IN-CELL （MP-PIC） METHOD

The mixing characteristics of dredged sediments of variable size discharged into cross-flow are studied by an Eulerian-Lagrangian method. A three-dimensional (3D) numerical model has been developed by using the modified k-ε parameterization for the turbulence in fluid phase/water and a Lagrangian method for the solid phase/sediments. In the model the wake turbulence induced by sediments has been included as additional source and sink terms in the k-ε model; and the trajectories of the sediments are tracked by the Lagrangian method in which the sediment drift velocities in cross-flow are computed by a multiphase particle-in-cell (MP-PIC) method and the diffusion process is approximated by a random walk model. The hydrodynamic behavior of dumped sediment cloud is governed by the total buoyancy on the cloud, the drag force on each particle and velocity of cross-flow. The cross-flow destroys more or less the double vortices occurred in stagnant ambience and dominates the longitudinal movement of sediment cloud. The computed results suggest satisfactory agreement by comparison with the experimental results of laboratory.     

气枪震源激发模式及应用

气枪震源是一种重要的人工地震震源。气枪阵列理论的提出,使得气枪阵列设计技术日趋成熟,并能够在石油勘探和地球物理探测中得到更加广泛的运用。气枪震源在不同领域中应用时,需要不同的组合和激发模式,以适应不同的探测要求。加强主脉冲和加强气泡脉冲,是目前两种主要的气枪激发模式。通过比较研究两种气枪激发模式,讨论各种激发模式在激发时间、气枪间距、频率、分辨率等方面的差异,为气枪震源的广泛运用提供依据。     

由井-含水层系统的水位动态反演含水层体应变

以孔隙弹性理论和水文地质学原理为基础,给出井水位波动与含水层介质体应变变化关系的数学表达式,结合固体潮理论分析了井—含水层系统水位潮汐波动对体应变固体潮的响应特征,用水位潮汐波来反演含水层体应变的变化,将反演结果与体应变实测资料得到的结果进行对比,发现二者有较好的一致性,说明用水位潮汐波来反演含水层体应变的方法是可行的,它为了解含水层的水文地质特性、体应变的变化及探索地震前兆提供了借鉴。