Period changes in the pulsating extreme helium stars V652 Her and BX Cir     

D. Kilkenny  L. A. Crause  F. van Wyk 《Monthly notices of the Royal Astronomical Society》2005,361(2):559-564

A new statement of the eigenvalue problem of studying small perturbations in arbitrary integrable self-gravitating systems is presented. An example of such a system, a 2D stellar disc, is considered in detail. The theory, based on the general equation for disc eigenmodes, reveals mechanisms for the formation and growth of global galactic structures. This new point of view specifies the limits of the unified theory of bar-like and spiral modes that was based on the assumption that global galactic structures could be understood in terms of low-frequency disc modes.  相似文献   

A Faraday rotation template for the Galactic sky     

Patrick Dineen  Peter Coles 《Monthly notices of the Royal Astronomical Society》2005,362(2):403-410

Using a set of compilations of measurements for extragalactic radio sources, we construct all-sky maps of the Faraday rotation produced by the Galactic magnetic field. In order to generate the maps, we treat the radio source positions as a kind of 'mask' and construct combinations of spherical harmonic modes that are orthogonal on the masked sky. As long as relatively small multipoles are used, the resulting maps are quite stable to changes in the selection criteria for the sources, and show clearly the structure of the local Galactic magnetic field. We also suggest the use of these maps as templates for cosmic microwave background (CMB) foreground analysis, illustrating the idea with a cross-correlation analysis between the Wilkinson Microwave Anisotropy Probe ( WMAP ) data and our maps. We find a significant cross-correlation, indicating the presence of a significant residual contamination.  相似文献   

Dissipationless mergers of elliptical galaxies and the evolution of the fundamental plane     

Michael Boylan-Kolchin  Chung-Pei Ma  Eliot Quataert 《Monthly notices of the Royal Astronomical Society》2005,362(1):184-196

We carry out numerical simulations of dissipationless major mergers of elliptical galaxies using initial galaxy models that consist of a dark matter haloes and a stellar bulge with properties consistent with the observed fundamental plane. By varying the density profile of the dark matter haloes [standard Navarro, Frenk & White (NFW) profile versus adiabatically contracted NFW profile], the global stellar to dark matter mass ratio and the orbit of the merging galaxies, we are able to assess the impact of each of these factors on the structure of the merger remnant. Our results indicate that the properties of the remnant bulge depend primarily on the angular momentum and energy of the orbit; for a cosmologically motivated orbit, the effective radius and velocity dispersion of the remnant bulge remain approximately on the fundamental plane. This indicates that the observed properties of elliptical galaxies are consistent with significant growth via late dissipationless mergers. We also find that the dark matter fraction within the effective radius of our remnants increases after the merger, consistent with the hypothesis that the tilt of the fundamental plane from the virial theorem is due to a varying dark matter fraction as a function of galaxy mass.  相似文献   

Crustal structure at the easternmost termination of the Variscan belt based on CELEBRATION 2000 and ALP 2002 data     

P. Hrubcov  P. roda  CELEBRATION Working Group 《Tectonophysics》2008,460(1-4):55-75

The eastern margin of the Variscan belt in Europe comprises plate boundaries between continental blocks and terranes formed during different tectonic events. The crustal structure of that complicated area was studied using the data of the international refraction experiments CELEBRATION 2000 and ALP 2002. The seismic data were acquired along SW–NE oriented refraction and wide-angle reflection profiles CEL10 and ALP04 starting in the Eastern Alps, passing through the Moravo-Silesian zone of the Bohemian Massif and the Fore-Sudetic Monocline, and terminating in the TESZ in Poland. The data were interpreted by seismic tomographic inversion and by 2-D trial-and-error forward modelling of the P waves. Velocity models determine different types of the crust–mantle transition, reflecting variable crustal thickness and delimiting contacts of tectonic units in depth. In the Alpine area, few km thick LVZ with the Vp of 5.1 km s^− 1 dipping to the SW and outcropping at the surface represents the Molasse and Helvetic Flysch sediments overthrust by the Northern Calcareous Alps with higher velocities. In the Bohemian Massif, lower velocities in the range of 5.0–5.6 km s^− 1 down to a depth of 5 km might represent the SE termination of the Elbe Fault Zone. The Fore-Sudetic Monocline and the TESZ are covered by sediments with the velocities in the range of 3.6–5.5 km s^− 1 to the maximum depth of 15 km beneath the Mid-Polish Trough. The Moho in the Eastern Alps is dipping to the SW reaching the depth of 43–45 km. The lower crust at the eastern margin of the Bohemian Massif is characterized by elevated velocities and high Vp gradient, which seems to be a characteristic feature of the Moravo-Silesian. Slightly different properties in the Moravian and Silesian units might be attributed to varying distances of the profile from the Moldanubian Thrust front as well as a different type of contact of the Brunia with the Moldanubian and its northern root sector. The Moho beneath the Fore-Sudetic Monocline is the most pronounced and is interpreted as the first-order discontinuity at a depth of 30 km.  相似文献   

Simultaneous transport of water and solutes under transient unsaturated flow conditions — A case study     

B. K. Purandara  N. Varadarajan  B. Venkatesh 《Journal of Earth System Science》2008,117(4):477-487

The imbalance between incoming and outgoing salt causes salinization of soils and sub-soils that result in increasing the salinity of stream-flows and agriculture land. This salinization is a serious environmental hazard particularly in semi-arid and arid lands. In order to estimate the magnitude of the hazard posed by salinity, it is important to understand and identify the processes that control salt movement from the soil surface through the root zone to the ground water and stream flows. In the present study, Malaprabha sub-basin (up to dam site) has been selected which has two distinct climatic zones, sub-humid (upstream of Khanapur) and semi-arid region (downstream of Khanapur). In the upstream, both surface and ground waters are used for irrigation, whereas in the downstream mostly groundwater is used. Both soils and ground waters are more saline in downstream parts of the study area. In this study we characterized the soil salinity and groundwater quality in both areas. An attempt is also made to model the distribution of potassium concentration in the soil profile in response to varying irrigation conditions using the SWIM (Soil-Water Infiltration and Movement) model. Fair agreement was obtained between predicted and measured results indicating the applicability of the model.  相似文献   

不整合运移通道类型及输导油气特征   总被引：12，自引：1，他引：11  

高长海  查明 《地质学报》2008,82(8):1113-1120

在对不整合空间结构特征研究的基础上,提出了油气沿不整合运移的通道类型:宏观上,存在由不整合面之上底砾岩和不整合面之下半风化岩石两种高效运载层组合成的双运移通道型和单运移通道型两种通道类型;微观上,底砾岩连通孔隙、半风化岩石构造卸荷风化裂缝系统及溶蚀孔洞系统可作为油气运移的主要通道。通过对不整合面上、下岩石物性分析,认为半风化岩石“孔洞缝”系统较底砾岩连通孔隙有更高的输导油气的能力。研究结果表明,不同的运移通道类型具有不同的输导油气特征。在地史时期,构造裂缝系统和溶蚀孔洞系统一直是不整合输导油气的主要通道;对于软地层构成的不整合来说,开始应是卸荷、风化裂缝系统和底砾岩连通孔隙共同构成不整合输导油气的主要通道,当上覆沉积载荷达到一定程度后,主要是底砾岩连通孔隙起输导油气通道作用;对于脆硬地层构成的不整合来说,卸荷、风化裂缝系统和底砾岩连通孔隙一直是不整合输导油气的主要通道。  相似文献   

蒙古塔木察格坳陷白垩系震积岩特征及其地质意义   总被引：5，自引：1，他引：4  

王化爱  钟建华  陈鑫  高玉飞 《地质学报》2008,82(8):1088-1094

通过岩芯观察,结合构造背景研究,在蒙古塔木察格坳陷白垩纪地层中识别出震积岩。震积岩的主要标志有微同沉积断裂、同沉积塑性变形构造、液化脉、震积枕状及伴生构造等。通过对塔219 井、塔1943 井等岩芯的系统观察,建立了蒙古塔木察格坳陷白垩系震积岩的垂向序列。震积岩的垂向序列自下而上依次为砂岩脉（砂火山）层段、水塑性褶皱变形层段、斧式构造层段、滑塌构造层段、阶梯状微断层和震裂缝层段、准原地沉积湖泊津浪丘状层理和内碎屑角砾岩层段、异地沉积震浊积岩层段,对应于地震由强变弱的一个变化过程。震积岩的发现具有重要的研究意义,有助于分析盆地边界断裂的强烈活动时期。  相似文献   

鄂尔多斯盆地东缘煤储层微孔隙结构特征及其影响因素   总被引：2，自引：0，他引：2  

张松航  汤达祯  唐书恒  许浩  林文姬  张彪 《地质学报》2008,82(10):1341-1349

在对鄂尔多斯盆地东缘58套采自不同层位不同地域煤样显微组分测试和低温液氮比表面测试的基础上,从比表面积、吸附曲线形态、阶段孔径结构分布、阶段孔径比表面积贡献、FHH分形特征几个方面刻画了煤储层微孔隙特征。同时,就“孔比表面积—孔隙结构—煤物质组成与化学结构”这一因果链,分析了鄂尔多斯盆地东缘煤微孔隙特征与煤变质程度、煤岩显微组分以及矿物组分与类型的关系。研究发现,Ro在0.60%~1.91%范围内,比表面积及FHH分形分维数先明显降低,Ro至1.3%后又略有回升,同时吸附回线“滞后环”及分形尺度对应的压力范围明显减小,孔径3~4 nm“墨水瓶”型孔明显减少乃至消失,并成为比表面积减少的主要贡献者。在相似煤级条件下,惰质组分较镜质组分有更多的比表面积贡献。粘土矿物组分含量>10%时,孔径3~4 nm“墨水瓶”型孔对比表面贡献明显,且随煤级增高影响作用相对加大。  相似文献   

煤岩对压裂裂缝长期导流能力影响的实验研究   总被引：7，自引：0，他引：7  

张士诚  牟善波  张劲  王雷 《地质学报》2008,82(10):1444-1449

煤层中一般都伴有煤层气,通过压裂可以将煤层气释放出来,一方面能够获得清洁能源,另一方面可以提高煤田的安全开采。煤岩层自身特点决定了其在压裂中应用的实验评价方法及结论应具有特殊性,本文主要针对煤层气井的煤岩层压裂裂缝长期导流能力进行实验评价研究。实验表明,与砂岩地层不同,煤岩的硬度较小,压裂中支撑剂嵌入情况较严重;煤岩易破碎,碎屑颗粒充填到支撑剂中;同时支撑剂存在破碎及吸附伤害等,多种作用导致支撑裂缝的导流能力降低。实验中,以煤岩层闭合压力为一个重要的参数,实验对比分析了在不同闭合压力下,铺砂浓度、支撑剂粒径、支撑剂种类及组合的选择、支撑剂颗粒的破碎与嵌入、压裂液残渣等因素对煤岩层导流能力的影响。本文的实验结论为,嵌入对煤岩层支撑裂缝的导流能力伤害很大,加大铺砂浓度、采用低破碎率支撑剂、降低压裂液伤害能在一定程度上提高煤层裂缝的导流能力,但影响程度随闭合压力的增加而逐渐降低。本文所得出的结论对今后煤层气的开发及设计施工具有一定的指导意义。  相似文献   

The relationship between hydrodynamic properties and weathering of soils derived from volcanic rocks,Galapagos Islands (Ecuador)     

M. Adelinet  J. Fortin  N. d’Ozouville  S. Violette 《Environmental Geology》2008,56(1):45-58

The aim of this interdisciplinary study is to examine a component of the hydrological cycle in Galapagos by characterizing soil properties. Nine soil profiles were sampled on two islands. Their physical and hydrodynamic properties were analyzed, along with their mineralogical composition. Two groups of soils were identified, with major differences between them. The first group consists of soils located in the highlands (>350 m a.s.l.), characterized by low hydraulic conductivity (<10⁻⁵ m s⁻¹) and low porosity (<25%). These soils are thick (several meters) and homogeneous without coarse components. Their clay fraction is considerable and dominated by gibbsite. The second group includes soils located in the low parts of the islands (<300 m a.s.l.). These soils are characterized by high hydraulic conductivity (>10⁻³ m s⁻¹) and high porosity (>35%). The structure of these soils is heterogeneous and includes coarse materials. The physical properties of the soils are in good agreement with the variations of the rainfall according to the elevation, which appears as the main factor controlling the soil development. The clayey alteration products constrain soils physical and hydrodynamic properties by reducing the porosity and consequently the permeability and also by increasing water retention.  相似文献